preview all symposia



Advanced materials and characterization techniques for solar cells III

Thanks to recent developments in photovoltaic research, cost/efficiency ratio of solar cells has been decreasing steadily. New efficiency records have been announced for various technologies, single crystalline, polycrystalline, and amorphous/crystalline tandem, CdTe, CIGS, CZTS, polymer, organic and most recently perovskite solar cells. These record efficiencies have been achieved partially thanks to advance characterization techniques that need to be further developed to decrease the cost/efficiency value. This symposium will provide a platform for discussion on the wide range of materials and characterization techniques used for advanced photovoltaics.


Photovoltaics provides renewable, clean, abundant and potentially low-cost energy. Recent drop in cost/efficiency ratio of electricity produced by photovoltaics allow more people to have access to clean energy. Photovoltaics is an area that is frequently highlighted by EU commission and takes place in Horizon 2020 targets under “competitive low-carbon energy” calls.

Silicon has been dominated the photovoltaics industry over several decades thanks to its superior properties and well-developed microelectronics industry based on it. Recently, very high efficiencies have been reported from solar cells fabricated using various materials such as CdTe, CIGS, perovskites, kesterites organics, III-V based multijunction, thin silicon. One most recent remarkable achievement is the increase the efficiency of perovskite solar cells from few percent to over 20% in a very short time period of 5 years. Characterization of solar cells and solar materials play an essential role in these developments together with choosing the right material. In addition, development of earth-abundant, low-cost materials and their characterization are important to reduce the cost/efficiency ratio further.

The focus of the proposed symposium is on areas of growth, modelling and characterization of solar materials and devices. Special emphasis will be given, but not limited, to the effect of the material properties on the device efficiency with particular interest on cells manufacturing, thin films, nanostructures, phenomena at interfaces, structural defects, bulk and surface properties, carriers transport properties, etc. The symposium aims at bridging the fundamental knowledge and information obtained from characterization techniques to developed solar cells with high efficiencies at lower costs.

All colleagues interested in the recent progresses and future challenges are invited to participate and encouraged to submit their contributions for oral and poster presentation.

Hot topics to be covered by the symposium:

  • Silicon-based wafer-scale solar cells
  • Thin-film silicon solar cells
  • CdTe and CIGS solar cells
  • Solar cells based on Kesterites
  • Perovskite solar cells
  • Tandem and heterojunction solar cells
  • Up- and down- converters
  • Light trapping
  • Photogenerated carriers transport and modeling
  • Surface and interface issues in solar cell design
  • Innovative materials for transparent contacts
  • Advanced glass and flexible substrates

List of invited speakers (confirmed):

  • Wim C. Sincke, ECN (state-of-the-art and future challenges for PV research)
  • Lucio Andreani, Univ. of Pavia (Light trapping and efficiency limits in crystalline silicon solar cells)
  • Aron Walsh, Bath Univ. (Advanced materials for PV)
  • John Schermer, Radboud University (III-V solar cells)
  • Iver Lauermann, HZB, (in-situ characterization of solar cells using synchrotron techniques)
  • Raphael Niepelt, ISFH (Crystalline silicon solar cells)
  • Franz-Jozef Haug, EPFL (Nanophotonics for photovoltaics)
  • Martin Schubert, Fraunhofer ISE (Photoluminescence characterization of solar cells)
  • Manuel João Mendes, CENIMAT-I3N (Photonic-enhanced solar cells with plasmonic and wave-optical dielectric nanostructures)
  • Bernd Stannowski, HZB (Advanced materials and processes for silicon heterojunction solar cells)
  • Stephanie Essig, NREL (GaInP/Si, 4-terminal tandem with 29.8% one-sun efficiency)

List of scientific committee members (confirmed):

  • Arthur Nozik (NREL, USA)
  • Jef Poortmans (IMEC, Belgium)
  • Gavin Conibeer (UNSW, Australia)
  • Salvo Mirabella (CNR-IMM, Italy)
  • Ayodhya Tiwari (EMPA, Switzerland)
  • Abdou Slaoui (MaCEPV, France)
  • Rasit Turan (METU, Turkey)
  • Antonio Terrasi (Università di Catania, Italy)
  • Thomas Krauss (York University, UK)
  • Sang II Seok (KRICT, South Korea)


The proceedings will be published in Energy Procedia - Elsevier
Solar Energy Materials and Solar Cells - Elsevier (selected manuscripts)

Start atSubject View AllNum.Add
Session 1 : Selcuk Yerci
Authors : Selcuk Yerci
Affiliations : The Center for Solar Energy Research and Applications, Middle East Technical University

Resume : Symposium T introduction

Authors : Wim C. Sinke
Affiliations : ECN Solar Energy, Petten, The Netherlands University of Amsterdam and FOM Institute AMOLF, Amsterdam, The Netherlands

Resume : Over the past decades, photovoltaic solar energy (PV) has made impressive progress in terms of conversion efficiency, cost and scale of deployment. This has been enabled by a powerful combination of research and technology development on the one hand and market incentives on the other hand. Improvements and breakthroughs could therefore be brought “from lab to fab to field”. In spite of this success, PV still makes a very modest contribution to global energy supply and therefore a big challenge still lies ahead of us. This presentation provides an overview of the state-of-the-art in PV science, technology, applications and describes the research challenges to be addressed to allow for competitive multi-terawatt deployment after 2020.

Authors : Seon Joo Lee, Seong Sik Shin, Young Chan Kim, Jun Hong Noh, Jangwon Seo,* and Sang Il Seok* (presenting author : Jangwon Seo)
Affiliations : Dr. Seon Joo Lee, Seong Sik Shin, Young Chan Kim, Dr. Jun Hong Noh, Dr. Jangwon Seo and Prof. Sang Il Seok Division of Advanced Materials Korea Research Institute of Chemical Technology 141 Gajeong-Ro, Yuseong-Gu, Daejeon 305-600, Republic of Korea E-mail: and Prof. Sang Il Seok School of Energy and Chemical Engineering Ulsan National Institute of Science and Technology (UNIST) 50 UNIST-gil, Eonyang-eup, Ulju-gun, Ulsan 689-798, Republic of Korea

Resume : For recent several years, significant progress has been successfully achieved in lead halide perovskite solar cells (PSCs), surpassing power conversion efficiency (PCE) of 20 %. Despite, toxicity issue of lead still remains for major obstacle to extend practical manufacturing production. To date, several attempts have been made to develop alternative divalent metal cation in perovskite analogues for replacing Pb2+ cation. The Kanatzidis and Snaith group reported the use of the methylammonium tin iodide (CH3NH3SnI3) as a light absorber in a typical n-i-p device consisting of mesoporous TiO2 scaffold and hole transporting material. However, those devices suffered from a rapid degradation against air and a poor reproducibility of the device performance. It is mainly attributed to the instability of Sn2+, which is easily oxidized into Sn4+. Very recently, Mathew et al. reported the use of formamidinium tin iodide (FASnI3) as a light absorber for solar cell application, and demonstrated a PCE of 2.1 % with the use of SnF2. For a better performance, it is essential to deposit uniform and dense perovskite layers and reduce Sn4+ content efficiently. In this work, we applied the solvent engineering process into Pb-free PSC to prepare a high quality of the perovskite film by homogeneous dispersion of SnF2. Consequently, we fabricated Pb-free PSC with high reproducibility, achieving a high power conversion efficiency of 4.8 %. Furthermore, the encapsulated device showed a good stability for over 100 days in air.

Authors : Antonio Abate
Affiliations : École Polytechnique Fédérale de Lausanne CH F1 493 (Bâtiment CH) Station 6, CH-1015, Lausanne, Switzerland University of Fribourg, Adolphe Merkle Institute Chemin des Verdiers 4, CH-1700, Fribourg, Switzerland

Resume : Organic-inorganic perovskites are quickly overrunning research activities in new materials for cost-effective and high-efficiency photovoltaic technologies. Since the first demonstration from Kojima and co-workers in 2009, several perovskite-based solar cells have been reported and certified with rapidly improving power conversion efficiency. Recent reports demonstrate that perovskites can compete with the most efficient inorganic materials, while they still allow processing from solution as potential advantage to deliver a cost-effective solar technology. Compare to the impressive progress in power conversion efficiency, stability studies are rather poor and often controversial. An intrinsic complication comes from the fact that the stability of perovskite solar cells is strongly affected by any small difference in the device architecture, preparation procedure, materials composition and testing procedure. In the present talk we will focus on the stability of perovskite solar cells in working condition. We will discuss a measuring protocol to extract reliable and reproducible ageing data. We will present new materials and preparation procedures which improve the device lifetime without giving up on high power conversion efficiency.

Authors : Alessandra Alberti (1), Ioannis Deretzis (1), Giovanna Pellegrino(1), Corrado Bongiorno(1), Emanuele Smecca(1), Giovanni Mannino(1), Filippo Giannazzo(1), Guglielmo Guido Condorelli (2), Nobuya Sakai(3), Tsutomu Miyasaka(3), Corrado Spinella(1) and Antonino La Magna (1)
Affiliations : (1) CNR-IMM Zona industriale, Strada VIII 5, 95121, Catania, Italy; (2) Università degli studi di Catania and INSTM UdR Catania V.le A.Doria 6 Catania, Italy; (3) Graduate School of Engineering, Toin University of Yokohama, 1614 Kuroganecho, Aoba, Yokohama 225-8503, Japan;

Resume : The kinetics of methyl-ammonium=MA ions play a crucial role in the properties of the MAPbI3 perovskite, one of most promising photovoltaic materials. Indeed, several evidences indicate that displacements and rearrangements of the MA ions rule the electrical properties, the phase transitions as well as the stability of MAPbI3. We have investigated this issue by means of ab-initio calculations, Car-Parrinello simulations, X-ray diffraction measurements and TEM structural analyses. Our theoretical study demonstrates that the spontaneous ordering process, which brings the MA ions to alternately point towards the centre of two out of the six faces of the cubic PbI3- framework, stabilizes at room temperature the tetragonal phase. Moreover, aging experiments at room temperature show that the reverse order to disorder transition, driving the starting tetragonal lattice in the direction of a cubic atomic arrangement, marks the early stage of the degradation process followed by a phase change towards PbI2. This structural destabilization precedes the volatilization of HI + CH3NH2 or MAI, with a relatively low energy cost, as ab-initio calculations indicate. The results of our analyses suggest a slight octahedral rearrangement after the loss of volatile species. Our experiments also clarify why reducing the interfaces and internal defects enhances the stability of the material. We finally discuss the impact of MA distribution on the electronic properties of the material.

Poster session 1 : Isodiana Crupi, Antonin Fejfar
Authors : Juae Kim,a Jihoon Lee,b Sangmin Chae,c Joo Young Shim,a Dal Yong Lee,b Hyo Jung Kim,c Sung Heum Park,b Hongsuk Suh a,*
Affiliations : aDepartment of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 609-735, Republic of Korea; bDepartment of Physics, Pukyong National University, Busan 609-735, South Korea; cDepartment of Organic Material Science and Engineering, Pusan National University, Busan 609-735, South Korea;

Resume : Polymer solar cells (PSCs) have many advantages of cost, easy roll-to-roll processibility and light-weight.1-2 We reified a concept of conjugated polymers consisting 2-pyriminecarbonitrile and 2-fluoropyrimidine and applied the PSCs. By Stille polymerization, we synthesized the new conjugated polymers, PTTICN, PTTICNR and PTTIFR. The optical band gaps from UV-vis absorption onset of PTTICN, PTTICNR and PTTIFR were about 2.0 eV. The HOMO energy levels of four polymers (PTTICN, PTTICNR and PTTIFR) were at -5.26 ~ -5.34 eV, their LUMO energy levels were at -3.47 ~ -3.50 eV, corresponding to the electrochemical band gap of around 1.8 eV. The device comprising PTTICN and PC71BM (1:4) with DIO showed a VOC of 0.82 V, a JSC of 6.38 mA/cm2, and a fill factor (FF) of 0.54, giving a power conversion efficiency of 2.81%. The device comprising PTTICNR and PC71BM (1:4) with DIO showed a VOC of 0.81 V, a JSC of 6.38 mA/cm2, and a fill factor (FF) of 0.43, giving a power conversion efficiency of 2.22%. The device comprising PTTIF and PC71BM (1:4) with DIO showed a VOC of 0.64 V, a JSC of 7.38 mA/cm2, and a fill factor (FF) of 0.55, giving a power conversion efficiency of 2.61%.

Authors : Zhiqiang Guan, Ho Wa Li, Jinfeng Zhang, Yuanhang Cheng, Qingdan Yang, Ming-Fai Lo, Sai-Wing Tsang*, Chun-Sing Lee*
Affiliations : Center of Super-Diamond and Advanced Films (COSDAF), City University of Hong Kong, Hong Kong SAR, P. R. China

Resume : The role of charge-transfer state (CTS) on charge separation process at donor/acceptor interface of organic solar cell (OSC) has been a hot topic in the last few years. How these interfacial states assist charge separation of Coulombically bound exciton by circumventing a few hundred meV binding energy and achieve near 100% internal quantum efficiency (IQE) is still puzzling. It is believed that the delocalization feature of CTS is crucial in the charge separation and the “hot” CTS is more delocalized than “relaxed” CTS. Here we elucidate the delocalization characteristics in different CTS manifolds by carrying out a modified charge-modulated electroabsorption spectroscopy (CMEAS) technique. By observing the similarly fast responses of CMEAS signals to the modulated electric field, we find “hot” and “relaxed” CTSs show a loosely bound feature, suggesting that both of them are delocalized states. This delocalization nature of CTS is further confirmed by comparing the CMEAS results of CTSs with those of the well-known localized polaron states. Our results indicates that there does not exist a substantial binding gradient in CTSs as described in Onsager model, rationalizing why near constant IQE values have been found for different energy excitations in OSCs. Moreover, this conclusion reveals that relaxation process from “hot” to “relaxed” CTSs would not weaken the delocalization feature of CTS, which is of crucial importance for the understanding of the role of CTS in photovoltaic process.

Authors : Gabrielė Jokubauskaite, Artiom Magomedov, Vytautas Getautis, Valentas Gaidelis, Vygintas Jankauskas, Egidijus Kamarauskas
Affiliations : Egidijus Kamarauskas;Department of Solid State Electronics, Vilnius University, Valentas Gaidelis; Department of Solid State Electronics, Vilnius University, Vygintas Jankauskas; Department of Solid State Electronics, Vilnius University, Vytautas Getautis; Department of Organic Chemistry, Kaunas University of Technology, Gabrielė Jokubauskaite; Department of Organic Chemistry, Kaunas University of Technology, Artiom Magomedov; Department of Organic Chemistry, Kaunas University of Technology,

Resume : Perovskite based Solar cells (SC) could provide an economic way to convert the Sun light into electricity, but a manufacturing of these Solar cells requires charge transporting materials like Spiro-OMETAD, which is hard to synthesize. A new carbazole based compound has been synthesized as a cheap replacement of Spiro-OMETAD. The perovskite based Solar cell containing this compound has been made and generated Uoc up to 0,75 V, jsc up to 14,9 μA/cm2 and reached an efficiency up to 8 percent. A Solar cell containing Spiro-OMETAD has been made in same manner as previous one and reached the same level of the efficiency. A charge mobility, an ionization potential and an absorbtion spectrum have been determined, as well as IPCE and APCE spectra. All these results will be presented in this poster.

Authors : Julius Važgėla, Gytis Juška, Kristijonas Genevičius
Affiliations : Department of Solid State Electronics, Vilnius University, Saulėtekio 9 III k.,10222 Vilnius, Lithuania

Resume : There are several different techniques to investigate charge carrier transport properties in organic solar cells such as time-of-flight (TOF), double injection (DoI), plasma extraction, charge extraction by linearly increasing voltage (CELIV), photo-CELIV and injection-CELIV (i-CELIV). However, only i-CELIV is suitable for both electron and hole electric field dependent mobility measurements even at low electric field. Since it is rather a new method, there are several drawbacks. First, the estimation of transit time is influenced by the ratio of semiconductor’s and insulator’s capacitances and it should be taken into account. Second, by using i-CELIV as well as CELIV or photo-CELIV, the determination of mobility dependence on electrical field is extremely approximate. We offered two correction coefficients which overcome those limitations and allow to measure electron and hole mobility dependence of electric field µ(E). Phenyl C61 butyric acid methyl ester (PCBM) and poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) bulk heterojunctions with different blend ratios were experimentally tested with i-CELIV method at different temperature. Electron and hole mobility activation energy was found for different ratio.

Authors : A. Delvallée1, K. Louarn1,2, D. Hapiuk3, F. Piquemal1, G. Almuneau2, A. Bounouh1
Affiliations : 1) LNE, Trappes, France; 2) LAAS-CNRS, Toulouse, France; 3) CEA-LETI, Grenoble, France

Resume : III-V material based multi-junction solar cells (MJSC) are the most advanced solution for high efficiency Solar Cells. These cells are designed so that each junction absorbs a separate portion of the energy spectrum, reaching conversion efficiency as high as 46%. However, these efficiencies are not high enough compare to the cost of such devices to compete with the traditional energy sources. Tunnel junctions are key devices in MJSC, and a good understanding of the quantum mechanisms of such structures is required to improve the MJSC efficiency. A numerical model of tunnel junction is being developed at LAAS and LNE and show so far good agreement with first MBE grown tunnel junction from LAAS. In this model, the doping levels of the tunnel junction are a key parameter and direct measurements of the carrier density on the sample are very relevant. That is why, in the framework of JRP ENG51 SolCell, we propose to realize quantitative nanoscale measurements on MJSC by using Scanning Microwave Microscopy (SMM). SMM could achieve high resolution measurements of electrical properties such as carrier density. In order to obtain reliable measurements, GaAs dopant staircase reference structure will be made by MBE at LAAS and the dopant density will be compared between SIMS (Secondary Ion Mass Spectrometry) and SMM measurements. Results obtained on tunnel junctions will be implemented in the numerical model.

Authors : K. Gwozdz (a), E. Placzek-Popko(a), M. Mikosza(a), E. Zielony(a), Z. Gumienny(a), R. Pietruszka(b), B. S. Witkowski(b), K. Kopalko(b), M. Godlewski(c)
Affiliations : (a)Department of Quantum Technologies, Faculty of Fundamental Problems of Technology, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland; (b)Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46, 02-668 Warsaw, Poland, (c)Department of Mathematics and Natural Sciences College of Science, Cardinal Stefan Wyszynski University,Dewajtis 5, 01-815 Warsaw, Poland

Resume : Recently cheap solar cells based on ZnO grown by ALD method on Si were developed[1]. However the efficiency is still low as compared to the commercially used solar cells. In our studies we attempt to find the reason of that by investigating the properties of defects in solar cells based on n-ZnO nanorods covered with Ag nanoparticles grown using a low-temperature hydrothermal method on p-type silicon substrates. The deep traps are studied by the DLTS method. Analysis of C-V characteristics preceding the DLTS studies let us conclude that the depletion region extends into the ZnO layer. Two deep traps are observed. Peak labeled as P1 of activation energy equal to 0.3eV and concentration of 0.004% of donor concentration (ND) has been assigned to the complex Vo-VZn[2]. The other, P2, of 0.2eV activation energy and much higher concentration (0.03%ND) has been linked with the n-ZnO/p-Si interface. In order to confirm this assignment, the Ti/p-Si Schottky junction was prepared. The signatures of deep traps observed for the diode (of activation energies: 0.09 eV, 0.38 eV and 0.54 eV) are different from the signatures of P1 and P2. We can conclude that the low efficiency of the solar cells is connected mainly with the defects present at the interface between ZnO and Si. In order to increase the efficiency the technological optimization is required. [1]R. Pietruszka at al, Thin Solid Films 563, 28 (2014). [2]G. Chicot et al , Physica Status Solidi (B) Basic Research 251, 206 (2014).

Authors : Jiangquan Mai, Tzs-Ki Lau, Xinhui Lu
Affiliations : Department of Physics, the Chinese University of Hong Kong

Resume : Ternary organic solar cells are emerging as a promising strategy to enhance organic photovoltaic device efficiency by broadening light absorption range. However, how to find compatible donor materials which allow comparable loadings of each component remains a challenge. In our work, we focus on studying the donor polymer compatibilities in ternary systems, employing grazing incident X-ray scattering technique to investigate the ternary morphology from molecular scale to nano scale. We find that morphology compatibility in terms of molecular packing and phase separation is the key to donor material selection which greatly extends the donor candidate pool for ternary organic solar cell research.

Authors : Masato Imai 1)2), Marin Watanabe 1)2), Akiko Mochihara 1)2), Himeka Tominaga 1), Yohei Yamaga 1), Kenji Yoshino 1)2), Yuhei Ogomi 2)4), Qing Shen 2)3), Taro Toyoda 2)3), and Shuzi Hayase 2)4)
Affiliations : 1) Department of Applied Physics and Electronics Engineering, Faculty of Engineering, University of Miyazaki; 2) CREST, Japan Science and Technology Agency (JST); 3) Department of Engineering Science, Faculty of Informatics and Engineering, The University of Electro-Communications; 4) Graduate School of Life Science and Systems Engineering, Kyusyu Institute Technology

Resume : Recently, there are many reports about the influences of ZnO buffer layer for an efficiency of solar cell. ZnO films of optoelectronic device quality have been synthesized by numerous techniques. In this study, non-doped ZnO thin films are deposited on various substrates, such as glass, Indium Tin Oxide (ITO) and F-doped Tin Oxide (FTO), by spray pyrolysis using Diethylzinc diluted with diisopropyl ether [1]. Depositions are conducted at the temperature between room temperature and 200°C while making N2 gas flow in atmospheric pressure. The optical and structural properties of ZnO films are characterized with spectrophotometer and X-ray diffraction. The density of each layer is evaluated by X-ray reflectometry. The surface morphological analysis are carried out using Scanning electron microscopy and atomic force microscopy. The results of characterization are summarized as follows; (1) The average optical transmittance is clearly above 80% in all samples. (2) ZnO films deposited at the temperature over 50°C are polycrystalline with a hexagonal wurtzite-type structure for all substrates. (3) The lattice parameter calculated is taken almost same value for every film. (4) Increasing deposited temperature results in higher grain size and higher density. (5) The density of ZnO films deposited over 100°C are fairly close to 5.68(g/cm2) of ZnO single crystal. (6) The surface roughness relates to the size of nanocrystallines. From these results, it is concluded that high quality ZnO films are synthesized. We consider that the ZnO film deposited by this spray pyrolysis is a promising candidate of buffer layer for solar cell. [1] K. Yoshino et al, Jpn. J. Appl. Phys. 50 (2011) 040207

Authors : Jian Qing, Hrisheekesh-Thachoth Chandran, Ming-Fai Lo, Chun-Sing Lee
Affiliations : Center of Super-Diamond and Advanced Films (COSDAF), City University of Hong Kong, Hong Kong SAR, P.R. China

Resume : We show the effects of chlorine incorporation in the crystallization process of perovskite film based on a lead acetate precursor. We demonstrate a fabrication process for fast grain growth with highly preferred {110} orientation upon only 5 minutes annealing at 100 oC. By studying the correlation between precursor composition and morphology, growth dynamic of perovskite film in the current system is discussed. In particular, we found that both lead acetate precursor and Cl incorporation are beneficial to perovskite growth. While lead acetate allows fast crystallization process, Cl improves perovskite crystallinity. Planar perovskite solar cells with optimized parameter deliver a best power conversion efficiency of 15.0% and average efficiency of 14.0% with remarkable reproducibility and good stability.

Authors : B. Bouadjemi *, S. Bentata*, T. Lantri *, Souidi Amel*, W.Bensaali*,A. Zitouni* and Z.Aziz*,
Affiliations : *Laboratory of Technology and of Solids Properties University of Abdelhamid Ibn Badis, Faculty of Sciences and Technology, Department, BP227 Mostaganem (27000) ALGERIA. E-MAIL :

Resume : We performed first-principle calculations, the full-potential linearized augmented plane wave (FP-LAPW) method is used to calculate structural, optoelectronic and magnetic properties of cubic halide perovskites CsPbX3 (X= F,I). We employed for this study the GGA approach and for exchange is modeled using the modified Becke-Johnson (mBJ) potential to predicting the accurate band gap of these materials. The optical properties (namely: the real and imaginary parts of dielectric functions, optical conductivities and absorption coefficient absorption make this halide perovskites promising materials for solar cells applications. Keywords: Halide perovskites, mBJ, solar cells, FP-LAPW, Optoelectronic properties and absorption coefficient.

Authors : W. El Huni[1], A. Migan[1, 2], Z. Djebbour[1, 3], A. Ougazzaden[4, 5], J-P. Salvestrini[6,7]
Affiliations : [1] GeePs, CNRS UMR8507, CentraleSupelec, Univ Paris-Sud, Université Paris-Saclay, Sorbonne Universités-UPMC, Gif-sur-Yvette, CEDEX, France. [2] Université Pierre et Marie Curie, UPMC, 4 Place Jussieu, 75005 Paris, France [3] Département des Sciences Physiques, UVSQ - Université Paris-Saclay, 45 Av des États-Unis, 78035 Versailles. [4] CNRS, UMI2958 Georgiatech-CNRS, Metz, France [5] Georgia Institute of Technology, 2–3 Rue Marconi, 57070 Metz, France [6] Université de Lorraine, LMOPS, EA4423, 2 Rue E. Belin, 57070 Metz, France [7] Centralesupélec, LMOPS, EA4423, 2 Rue E. Belin, 57070 Metz, France

Resume : InGaN material has known a promising progress these past years not only for Light Emitting Diode (LED) technology, but also for photovoltaic. This material has a wide-range direct adjustable bandgap from 0.7eV for InN to 3.44eV for GaN, which covers the totality of solar spectrum[1]. This property leads to the possibility of fabricating a multi-junction solar cell with the same material that covers completely the solar spectrum. Alternatively, it can be combined with other inexpensive material as a wide bandgap top junction to make low-cost high efficiency solar cells[2]. However, several challenges should be overcome in order to reach a high-efficiency InGaN-based solar cell, among others the growth of good-quality relatively thick absorbing layer[3]. Thanks to Multi-Quantum Well structure (MQW) inspired from LED technology, recently a solar cell with 20% of indium has been achieved with an open-circuit voltage (Voc) of 2.4V and fill factor (FF) of 80% [4] . In this communication, using an advanced realistic simulation TCAD tool, we have reproduced the experimental results obtained by Ref [4] and carried out a complete study of the influence of various parameters on the performance of the solar cell (e.g barriers’ thickness, wells’ thickness, number of periods, doping levels …etc.) in order to optimize the structure and to show the possible paths that might conduct to improve its efficiency. We have considered different indium incorporation taking into account the real critical thickness at each indium composition. We have shown that for indium composition higher than 30% of indium, the InGaN-based solar cell’s efficiency start to decrease due to the decrease in tunnelling probability that is proportional to barriers’ height and thickness. [1] I. Vurgaftman et al. APPLIED PHYSICS REVIEWS vol. 3675, no. 2003, 2005. [2] L. Hsu et al. J. Appl. Phys., vol. 104, no. 2, p. 024507, 2008. [3] K. Pantzas et al. J. Cryst. Growth, vol. 370, pp. 57–62, May 2013. [4] Young et al., Appl. Phys. Lett., vol. 103, no. 17, p. 173903, 2013.

Authors : Shao-Sian Li(a), Chi-Huang Chang(a), Ying-Chiao Wang(a), Chung-Wei Lin(a), Di-Yan Wang(b), Jou-Chun Lin(b), Chia-Chun Chen(b), Hwo-Shuenn Sheu(c), Hao-Chung Chia(d), Wei-Ru Wu(c), U-Ser Jeng(d), Chi-Te Liang(a), Raman Sankar(a), Fang-Cheng Choug(a), Chun-Wei Chen(a)
Affiliations : (a)National Taiwan University; (b)National Taiwan Normal University; (c)National Synchrotron Radiation Research Center, Taiwan; (d)National Tsing-Hua University, Taiwan

Resume : This work proposes a novel approach to modulate the nucleation and growth of perovskite crystals in planar perovskite (CH3NH3PbI3?xClx) solar cells by intermixing precursor-capped inorganic nanoparticles of PbS. A small amount of dispersed PbS nanoparticles which were covered with perovskite precursor molecules of methylammonium iodide (CH3NH3I, MAI) through the ligand-exchange treatment functioned as effective seed-like nucleation sites to promote the formation of perovskite lattice structures. Through this intermixing-seeded growth technique, substantial morphological improvements, such as increased crystal domains, enhanced coverage, and uniformity, were realized in the perovskite thin films, and the corresponding solar cell devices exhibited a promising power conversion efficiency of 17.4%, showing an enhancement of approximately 25% compared to that of the controlled pristine solar cell device. The substantially enhanced crystal orientation, particularly along the direction perpendicular to the substrate, was evident from the synchrotron-based grazing incidence wide-angle X-ray scattering data. This observation was consistent with the enhanced carrier diffusion lengths and excellent reproducibility of high fill factors of the planar heterojunction perovskite devices fabricated through the proposed technique.

Authors : Douglas J. Coutinho (1), Francineide L. Araújo (2), Daniel R. B. Amorim (2), Dennis G. Brenes-Badilla (3), Maria C. Salvadori (3), and Roberto M. Faria (2).
Affiliations : (1) Federal University of Technology - Paraná (Brazil) (2) São Carlos Institute of Physics/University of São Paulo (Brazil) (3) Institute of Physics/University of São Paulo (Brazil)

Resume : A series of bulk-heterojunction organic solar cells that exhibited a good performance were fabricated with regio-regular poly(3-hexylthiophene) (rr-P3HT) or poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b:4,5-b0](dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno [3,4-b] thiophene)-2,6-diyl] (PBDTTT-EFT) as the donor and with [6,6]phenyl-C61-butyric acid methyl ester (PC71BM) or [6,6]phenyl-C71-butyric acid methyl ester (PC71BM) as the acceptor. Effects of measurements of the photovoltaic J-V curves under simulated AM1.5G irradiation (100mW/cm2), photo-CELIV, and the transient photovoltage (TPV), carried out at different temperatures (100–340 K), combined with an analytical modeling for the photocurrent provided us to investigate the influence of the mobility (μ) and lifetime (τ) of the charge carriers on the short-circuit current (Jsc) , the fill factor (FF), and the power conversion efficiency (PCE) of both solar cell structures. We conclude that for voltages close to the open-circuit voltage (Voc), non geminate recombination is the main loss factor in a BHJ-OSC, while as the photocurrent approaches its saturated value, the loss factor is essentially defined by the dissociation probability (P) of the charge transfer states (CTC states). We also show that the ratio between the drift length (µτE) and the thickness L of the active layer plays an important role in the determination of charge transport and in the efficiency of charge carrier extraction by the electrodes. Degradation caused by the interaction of oxygen with molecules of the active layer and water at the PEDOT:PSS/active layer interfaces were also analyzed and discussed.

Authors : Jeongho Park, Hyunho Shin, Jaekwang Jung and Sungwon Hwang
Affiliations : Department of Nano Science and Mechatronics Engineering and Interdisciplinary Research center for health and Nanotechnology Research Center, Konkuk University, Chungju, Chungbuk 380-701, Korea

Resume : The Graphene optoelectronic devices such as displays, touch screens, light-emitting diodes and solar cells require materials with low sheet resistance and high transparency. The graphene quantum dots/Ag nanowires provide superior charge collection in the nanocomposites. For the application of graphene quantum dots (GQDs) to optoelectronic nano-devices, it is of critical importance to understand the mechanisms which result in novel phenomena of their light absorption/emission. We demonstrate bright, efficient, and graphene quantum dots/Ag nanowires nanocomposites perovskite nano-devices through the direct charge carrier collection into GQDs and the efficient radiative exciton recombination within QDs. Graphene quantum dots (GQDs) have received much attention due to their novel phenomena of charge transport and light absorption/emission. Thus, the demonstration of photovoltaic efficiency with GQDs would be the basis for a plenty of applications not only as a flexible device in perovskite nano-devices but also a key component in the optoelectronic integrated circuits. The enhancements of short-circuit current density and photoelectric conversion efficiency are attributed to the increase of light coupling and thus the light absorption of the dye due to the localized surface plasmon resonance and the possible enhanced light scattering of graphene quantum dots/Ag nanowires.

Authors : R. Pietruszka1, B.S. Witkowski1, R. Schifano1, K. Kopalko1, T. Krajewski1, S. Gieraltowska1, E. Zielony2, K. Gwozdz2, P. Bieganski2, E. Placzek-Popko2, M. Godlewski1,3
Affiliations : 1Institute of Physics, Polish Academy of Sciences, Warsaw, Poland 2Faculty of Fundamental Problems of Technology, Wroclaw University of Technology, Wroclaw, Poland 3Department of Mathematics and Natural Sciences College of Science, Cardinal Stefan Wyszynski University, Warsaw, Poland

Resume : ZnO, a wide band gap semiconductor with 3.3 eV band gap at room temperature, is intensively studied for photovoltaic (PV) applications - mostly as a transparent conductive oxide (TCO) and/or as a n type partner for p-type materials (e.g. Si, CdTe, CIGS…). In this work, we study PV structures based on n type ZnO layers grown by atomic layer deposition method (ALD) and ZnO nanorods grown by a hydrothermal method on p-type Si wafers (2 Ωcm; (100)). We focused on the photovoltaic effect in solar cells (SC) based on n ZnO/p Si heterojunction. Since a conduction band offset appearing in n-ZnO/p-Si heterojunction SC is recognized as a serious roadblock to obtain high PV response, we used magnesium doped zinc oxide layers (ZnxMgx-1O) instead of ZnO. This influences the energy band diagram and enhances cell efficiency. The PV efficiency for AZO/Znx-1MgxO/ Si/Al structure is 10.5%. For PV structures containing ZnO nanorods more efficient SC were obtained. The PV efficiency for such a “new-generation” structures (ZnO:Al/ZnO/ZnONR/Si/Al) equals 14%. This work was partially supported by the National Science Center (decision No.DEC-2012/06/A/ST7/00398), and (Wroclaw group) by the National Laboratory of Quantum Technologies (POIG.02.02.00-00-003/08-00) and Statutory grant S400291.

Authors : Marie Buffière1, Adnan Ali1, Abdel-Aziz El Mel2, Eric Gautron2, Khaled Mahmoud1, Pierre-Yves Tessier2 and Ahmed Ennaoui1
Affiliations : 1 Qatar Environment and Energy Research Institute (QEERI), HBKU, Qatar Foundation, Doha, Qatar 2 Institut des Matériaux Jean Rouxel, IMN, Université de Nantes, CNRS, 2 rue de la Houssinière B.P. 32229, 44322 Nantes cedex 3, France

Resume : In the standard thin film solar cell structure, the top contact is based on transparent conductive oxide (TCO) thin film deposited by vacuum based deposition techniques. Indium Tin Oxide (ITO), Aluminium doped Zinc Oxide (AZO) and fluorine doped Tin Oxide (FTO) thin films are the commonly used TCO for this application. However, the poor mechanical stability of such materials is a real hurdle making impossible to integrate such electrodes in flexible solar cells. Furthermore, as most of photovoltaic (PV) technologies are evolving towards printing approaches, replacing the conventional deposition process by low-cost, up-scalable and non-vacuum based methods is becoming necessary. In this contribution, we have used calcinated nanofibers, synthesized by electrospinning, to produce stable and flexible electrodes for thin film solar cells. The impact of the size, shape and composition of the nanofibers on their transparency and resistivity is investigated by SEM, TEM, XPS and optoelectrical analysis. Furthermore, the integration of the nanofibers based electrodes in kesterite thin film solar cell devices is demonstrated.

Authors : Alessandro Stroppa1, Domenico Di Sante1,2, Paolo Barone1, Menno Bokdam3, Georg Kresse3, Cesare Franchini3, Myung-Hwan Whangbo4, Silvia Picozzi1
Affiliations : 1 Consiglio Nazionale delle Ricerche—CNR-SPIN, I-67100 L’Aquila, Italy. 2 Department of Physical and Chemical Sciences, University of L’Aquila, I-67100 L’Aquila, Italy. 3 Faculty of Physics, Center for Computational Materials Science, University of Vienna, A-1090 Wien, Austria. 4 Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, USA.

Resume : Using density functional theory simulations and symmetry analysis, we show that the lead-free perovskite iodide (FA)SnI3, containing the planar formamidinium cation FA, (NH2CHNH2)+ , is ferroelectric. In fact, the perpendicular arrangement of FA planes, leading to a ‘weak’ polarization, is energetically more stable than parallel arrangements of FA planes, being either antiferroelectric or ‘strong’ ferroelectric. Moreover, we show that the ‘weak’ and ‘strong’ ferroelectric states with the polar axis along different crystallographic directions are energetically competing. Therefore, at least at low temperatures, an electric field could stabilize different states with the polarization rotated by pi/4, resulting in a highly tunable ferroelectricity appealing for multistate logic. Intriguingly, the relatively strong spin–orbit coupling in noncentrosymmetric (FA)SnI3 gives rise to a co-existence of Rashba and Dresselhaus effects and to a spin texture that can be induced, tuned and switched by an electric field controlling the ferroelectric state.

Authors : Won-Yong Jin, Jae-Wook Kang*
Affiliations : Department of Flexible and Printable Electronics, Chonbuk National University, Jeonju 561-756, Republic of Korea

Resume : We report a novel architecture to fabricate all solution-processed flexible transparent conducting electrodes by using a combination of metal sub-electrodes embedded into flexible substrate and ultrathin transparent conducting layer (ME-TCEs). The use of the silver metal sub-electrode and the PEDOT:PSS layer in combination resulted in an increase in conductivity subsequently improve the transmittance and helped in overcoming the trade-off between them. The fabricated ME-TCEs are highly transparent (optical transmittance > 83% at a wavelength of 550 nm), highly conducting (sheet resistance ~3.0 ohm/sq.) and extremely flexible (bending radius ~500 μm) electrodes with very smooth surface (root-mean-square roughness ≈0.5 nm). The flexible organic solar cells fabricated using ME-TCEs showed high power conversion efficiency of ~7.46 %, which is higher performance with ITO-based devices (~7.00%). Moreover, the devices made using the ME-TCEs showed almost same device performance even after being bent 1000 times with a radius of ~1.0 mm.

Authors : Riski Titian Ginting, Won-Yong Jin, Jae-Wook Kang*
Affiliations : Department of Flexible and Printable Electronics, Chonbuk National University, Jeonju 561-756, Republic of Korea

Resume : The solution processed methylammonium lead iodide (MAPbI3)-perovskite solar cells (PSCs) was fabricated based on low temperature sol-gel ZnO as electron transporting layer with full device structure of ITO/ZnO/MAPbI3/Spiro-OMeTAD/Ag. Based on the J-V measurement, the average power conversion efficiency was significantly improved from 13.36 up to 14.48 % with decreasing of temperature from 298 K to 253 K primarily caused by the increment short-circuit current density and open-circuit voltage. Similar trend of device performance was observed even without ZnO layer (ITO/MAPbI3/Spiro-OMeTAD/Ag). The improvement of photocurrent is related to the high charge carrier mobility and shorter electron transport lifetime at lower temperature. Interestingly, the degree of hysteresis decreases as temperature cooled down to 253 K which correlated to the ion migration effect within the perovskite layer and evidently explained by employing transient chronoamperometry measurements.

Authors : Yoonseok Oh, Myeongkyu Lee
Affiliations : Department of material science engineering, Yonsei university, Republic of Korea

Resume : Research area of perovskite hybrid solar cells has recently grown up tremendously for several years because of its high photovoltaic performance of inorganic-organic lead halide hybrid perovskite. Despite its amazing photovoltaic performance, there are some challenges of perovskite hybrid solar cells to overcome air and moisture instability. Here, we report a method for enhancing moisture stability by improving crystallinity of CH3NH3PbI3 by laser irradiation. In two-step deposition of CH3NH3PbI3, morphology of PbI2 is an important factor of moisture stability of CH3NH3PbI3. So, the PbI2 layer was irradiated by Nd:YV04 UV pulse laser and dipped into CH3NH3I/2-propanol solution. As PbI2 layer was melted by laser irradiation, crystallinity and uniformity of CH3NH3PbI3 was improved, observed by field emission scanning electron microscopy(FE-SEM) images. Also, air and moisture stability of CH3NH3PbI3 were increased. Further experiments should be done to figure out the reasons of crystallinity and stability improvement.

Authors : Po-Ruei Yan, Wei-Jie Huang, Sheng-Hsiung Yang
Affiliations : Institute of Lighting and Energy Photonics, National Chiao Tung University

Resume : The goal of this research is to fabricate air-stable inverted perovskite solar cells by incorporating quaternary ammonium salts in [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as electron transporting layer. The selection of ammonium salts includes tetrabutylammonium bromide (TBABr), tetrabutylammonium tetrafluoroborate (TBABF4), and tetrabutylammonium hexafluorophosphate (TBAPF6). Inverted perovskite solar cells with the configuration of ITO/PEDOT:PSS/CH3NH3PbI3/PCBM+salts/Ag were fabricated, without using active metals such as calcium or magnesium. All devices were characterized under standard AM1.5G illumination condition in the ambient environment without encapsulation. The devices were remarkably enhanced by introducing TBABF4 or TBAPF6 in PCBM, revealing an open-circuit voltage (VOC) of 1.0V, a short-circuit current density (JSC) of 18.79 mA/cm2, a FF factor of 72%, and power conversion efficiency (PCE) of 13.41%, as compared with the un-doped device (VOC = 0.92 V, JSC = 16.89 mA/cm2, FF = 54%, and PCE = 8.42%). The second part of this research is to study the effect of those additives on the device performance via different techniques, including 4-point probe measurement, AFM, UPS, PL decay experiment, and mobility calculation. It is concluded that salt additives help to increase the conductivity and carrier mobility of PCBM layer; furthermore, the interfacial contacts between perovskite/PCBM and PCBM/Ag are also modified, which lead to improved JSC and FF values of devices.

Authors : A.Smida, R.Riahi, N.H.mohamed, F.Laater, M.Hassen, H.Ezzaouia
Affiliations : Photovoltaic Laboratory of Centre for Research and Energy Technologies

Resume : Synthesized-CdSe nanoparticles were deposited by using spin coating method onto porous GaAs substrate elaborated by an electrochemical process. Surface morphology and surface roughness of the deposited CdSe layers was investigated by scanning electron microscopy (SEM) and Atomic Force Microscopy (AFM). SEM imaging shows an inhomegenity distribution of CdSe nanoparticles; which can be related to the non uniformity of the pores on the GaAs ‘surface. In addition, the CdSe was penetrated deeply in the porous structure down to the bottom and reaching the interface GaAs/porous GaAs. AFM exhibits that the CdSe layer deposited on porous Gas substrate has more roughness. X- ray diffraction (XRD) technique proves the incorporation of CdSe nanoparticles on the surface states. It was also observed that the reflectivity decreased due to the appearance of roughness which is in agreement with the SEM and AFM analysis. Also, the photoluminescence (PL) spectroscopy exhibits a new intense peak centered at 2.08 eV related to CdSe nanoparticles about 2nm of diameter which was determined by using effective mass approximation model from effective band gap. Keywords: Porous GaAs, Cadmium selenium (CdSe), SEM, UV-Visible.AFM, Pl, XRD

Authors : Sevki Can Cevher a*, Cansel Temiz b, Gonul Hizalan a, Yasemin Arslan Udum c, , Levent Toppare a,b,d,e, Ali Cirpan a,b,d,e,f
Affiliations : aDepartment of Chemistry, Middle East Technical University, 06800 Ankara, Turkey; bDepartment of Polymer Science and Technology, Middle East Technical University, 06800 Ankara, Turkey; cInstitute of Science and Technology, Department of Advanced Technologies, Gazi University, Ankara 06570, Turkey; dDepartment of Biotechnology, Middle East Technical University, 06800 Ankara, Turkey; eThe Center for Solar Energy Research and Application (GUNAM), Middle East Technical University, 06800 Ankara, Turkey; fDepartment of Micro and Nanotechnology, Middle East Technical University, 06800 Ankara, Turkey

Resume : This study demonstrates that, modifying the rigidity and structural changes on the polymeric materials dictate the optic and electronic properties. Three different conjugated quinoxaline and benzotriazole based polymers were synthesized via Stille cross coupling chemical polymerization method. All changes were localized on the quinoxaline moiety of the conjugated polymers. Characterizations of polymers were done in terms of molecular weight (GPC), absorption wavelengths (Uv-vis spec.), and electronic properties (CV). After all characterizations, polymers were used as photoactive materials, for ultimate purpose, to construct solar cell. Broad absorption of polymers were found as great candidate for electrochromic devices due to 60 % and 94 % percent transmittance in NIR region respectively P2 and P3 with less than 1s switching time. The highest PCE was reported as 2.13 % for P1 with high short circuit current (8.07 mA/cm2), moderate open circuit voltage (0.53 V), low fill factor (50%) and sufficient incident photon to current efficiency (38.33 %). P2 and P3 also showed reasonable PCE value as 1.77 % and 0.95 % respectively.

Authors : İpek Önk a, Cagla Istanbulluoglu a,* Gonul Hizalan a, Serife O. Hacioglu a, Şevki Can Cevher a, Ali Cirpan a,b,c and Levent Toppare a,b,c,d
Affiliations : a Department of Chemistry, Middle East Technical University, 06800 Ankara, Turkey; b The Center for Solar Energy Research and Application (GÜNAM), Middle East Technical University, 06800 Ankara, Turkey; c Department of Polymer Science and Technology, Middle East Technical University, 06800 Ankara, Turkey; d Department of Biotechnology, Middle East Technical University, 06800 Ankara, Turkey; *

Resume : A novel 2-(2-nonyltridecyl)-4,7-di(selenophen-2-yl)-2H and isoindole 9-(heptadecan-9-yl)-9H-carbazole containing D-A type alternating copolymer was synthesized via Suzuki coupling polymerization. NMR Spectroscopy was used to prove structure of the polymer. Number average molecular weight of the polymer was determined as 10800 g/mol. Branched alkyl chain groups were incorporated into polymer backbone in order to increase the solubility of the polymer in common organic solvents such as chloroform and 1,2-dichlorobenzene.1 In addition, selenophene was comprised into polymer backbone as a -bridge in order to increase intramolecular interactions due to high polarizability of selenium atom. Moreover, electron donating ability of the selenophene increases the charge carrier mobility of the polymer. The electrochemical and optical properties of polymer were investigated and the polymer showed ambipolar (both p- and n- dopable) characteristic. HOMO and LUMO levels were calculated as -5.95 and -3.75 eV from cyclic voltammogram and the electronic band gap was calculated as 2.2 eV. The polymer exhibits strong absorption band at 485 nm with a shoulder at 522 nm. In order to investigate photovoltaic properties of the P1, polymer was blended with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). Current density–voltage (J–V) characteristics of photovoltaic cells were measured under the illumination of simulated solar light with 100mW cm-2 (AM 1.5G). 1.07 % PCE was obtained with a high open-circuit voltage of 0.78 V and a Jsc of 3.15 mA/cm2, and a FF of 44% with a device structure of ITO/PEDOT:PSS/Polymer:PC71BM /LiF/Al. REFERENCES 1) X. Zhang, L. J. Richter, D. M. DeLongchamp, R. J. Kline, M. R. Hammond, I. McCulloch, M. Heeney, R. S. Ashraf, J. N. Smith, T. D. Anthopoulos, B. Schroeder, Y. H. Geerts, D. A. Fischer, and M.F. Toney, " Molecular Packing of High-Mobility Diketo Pyrrolo-Pyrrole Polymer Semiconductors with Branched Alkyl Side Chains " J. Am. Chem. Soc. 2011, 133, 15073–15084 2) D. Meng, D.Sun, C. Zhong, T. Liu, B.Fan, L. Huo, Y. Li, W. Jiang, H. Choi, T. Kim, J. Y. Kim, Y. Sun, Z. Wang, and A. J. Heeger, " High-Performance Solution-Processed Non-Fullerene Organic Solar Cells Based on Selenophene-Containing Perylene Bisimide Acceptor " J. Am. Chem. Soc. 2016, 138, 375−380

Authors : Ho-Wa Li, Qing-Dan Yang, Zhiqiang Guan, Yuanhang Cheng, Taili Liu, Tsz-Wai Ng, Chun-Sing Lee, Sai-Wing Tsang
Affiliations : Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR, P. R. China

Resume : Energy level alignment at organic donor and acceptor interface is a key to determine the photovoltaic performance in organic solar cells, but direct probing such energy alignment is still challenging especially for solution processed bulk heterojunction (BHJ) thin films. Here we report a systematic investigation on probing the energy level alignment with different approaches in five commonly used polymer:[6,6]-phenyl-C71-butyric acid methyl ester (PCBM) BHJ systems. We find that by tuning the weight ratio of polymer to PCBM, the electronic features from both polymer and PCBM can be obtained by photoemission spectroscopy. Using this approach, we find that some of the BHJ blends simply follow vacuum level alignment, but others show strong energy level shifting as a result of Fermi level pinning. Independently, by measuring the temperature dependent open-circuit voltage (VOC), we find that the effective energy gap (Eeff), the energy difference between the highest occupied molecular orbital of the polymer donor (EHOMO-D) and lowest unoccupied molecular orbital of the PCBM acceptor (ELUMO-A), obtained by photoemission spectroscopy in all polymer:PCBM blends has an excellent agreement with the extrapolated VOC at 0 K. Consequently, the photo-voltage loss of various organic BHJ photovoltaic devices at room temperature is in a range of 0.3 V to 0.6 V. It is believed that the demonstrated direct measurement approach of the energy level alignment in solution processed organic BHJ will bring deeper insight into the origin of the VOC and the corresponding photo-voltage loss mechanism in organic photovoltaic cells.

Authors : Byung-Sung Kim, † Darren C. J. Neo, ‡ Bo Hou, † Jong Bae Park, †,§ Yuljae Cho, † Nanlin Zhang, ‡ John Hong, † Sangyeon Park, † Sanghyo Lee , † Jung Inn Sohn, † Hazel E. Assender, ‡ Andrew A. R. Watt, ‡ SeungNam Cha, † Jong Min Kim†
Affiliations : † Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK ‡ Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, U.K § Jeonju centre, Korea Basic Science Institute, Jeonju, Jeollabuk-do 561-180, Republic of Korea

Resume : Hybrid colloidal quantum dot (CQD) solar cells are fabricated from multi-layer stacks of single layer graphene (SG) and lead sulfide (PbS) CQD. The inclusion of graphene inter-layers increases the power conversion efficiency as well as current density, considerably. It is shown that the inclusion of conductive graphene enables efficient charge extraction in devices. Photoluminescence shows that graphene quenches emission from the quantum dot suggesting spontaneous charge transfer to graphene. CQD photodetectors show increased photoresponse and improved transport properties. We propose that the SG-CQD composite is a route to make CQD thin films with improved charge extraction, therefore resulting in improved solar cell efficiency.

Authors : Mihaela Girtan
Affiliations : LPHIA - Photonics Laboratory, LUNAM, Angers University, 2.Bd. Lavoisier, 49045, France

Resume : The influence of the metallic cathode geometry was investigate for ITO/PEDOT:PSS/PCDTBT:PCBM/Al and ITO/PEDOT:PSS/P3HT:PCBM/Al solar cells. ITO coated glass substrates were subsequently cleaned with ethanol followed by multiple rinsing in de-ionized water. PEDOT:PSS films were deposited by spin coating at velocities comprised between 1000 RPM and 1500 RPM. P3HT highly regioregular (> 98%) poly(3-hexylthiophene-2,5-diyl) purchased from Rieke Metals, PCDTBT - Poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] purchased from Ossila and PCBM - Methanofullerene Phenyl-C61-Butyric-Acid-Methyl-Ester purchased from SES research were used for the preparation of active layers. P3HT:PCBM films (1:0.8 wt %) and PCDTBT:PCBM films (1:4 wt %) were spin coated from chlorobenzene solutions on ITO electrodes using spinner speeds between 400 RPM and 450 RPM. After spin-coating the samples were dried in oven for 20 min at 110°C. Current–voltage (I–V) characteristics in dark and under illumination were measured using a Keithley 2400 source measurement unit. For the characterization under illumination was done using a white light from a AM 1.5 solar simulator (Lot Oriel) at 1000W/m2. Different mask sizes placed at different distances from the cathode were used in order to study the influence of the irradiation distance and cathode configuration. If we expected to find a decrease of the short-circuit current with the increase of the distance between the cathode and the irradiation area, we also put in evidence that the open-circuit voltage also highly depend on the irradiation geometry.

Authors : Yi-Chin Liao 1, Tzung-Fang Guo 2, Yao-Jane Hsu 2, 3 and Ten-Chin Wen 1*
Affiliations : 1 Department of Chemical Engineering, 2 Department of Photonics, National Cheng Kung University, Tainan, 70101, Taiwan; 3 National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu, Taiwan

Resume : Interfacial modification is critical to maximize the efficiency of polymer light-emitting diodes (PLEDs) and polymer solar cells (PSCs). Herein, we demonstrate highly efficient PLEDs and PSCs with a series of novel zwitterionic molecules, including trioctylsulfobetaine (TOS), tridodecylsulfobetaine (TDS), and etc. as solution-processed interfacial layers. Polyfluorene Green B (G-PF) was used as the active layer in PLEDs 0while the blend of PTB7-Th:PC71BM was employed in PSCs. Interestingly, the PLEDs with TOS exhibit the highest performance. To further understand the mechanism, the devices using TOS were compared with the devices using tetraoctylammonium bromide (TOAB), which is an effective electron injection layer. For the PLED device with the TOS/Al cathode shows the higher luminance (77535 cd m-2) and luminance efficiency (13.1 cd A-1) than that with TOAB/Al (52871 cd m-2, 11.6 cd A-1) and Ca/Al cathodes (38543cd m-2, 5.1cd A-1). We have studied the temperature effect of both TOS and TOAB, and the results show that the device with TOS/Al cathodes still maintain high performance, while those with TOAB/Al cathodes decreases dramatically when increased to 100℃. Apart from the enhanced electron injection via TOS, TOS significantly improves the electron extraction and renders the PSC device based on the active layer of PTB7-Th:PC71BM the high PCE of 9.84% (PCEavg: 9.7%). The PCE enhancement is 41.8%, compared to the PCE of the device with the Ca/Al cathode (PCEavg:6.84%).

Authors : Marek Lipinski, Katarzyna Gawlinska, Grazyna Kulesza-Matlak, Zbigniew Starowicz, Lukasz Major, Kazimierz Drabczyk
Affiliations : Institute of Metallurgy and Materials Science, Polish Academy of Sciences

Resume : There is a great interest in developing of hybrid organometallic halide perovskites solar cell. The main goal of this work is to investigate the influence of the air moisture, temperature of deposition and different additions on the optical and structural properties of MAIPbI3 and MAIPbI3-xClx halide perovskites. The perovskite solar cells were made in two architectures with the planar and with mesoporous skeleton structure. The optical properties of the obtained structures are investigated using UV-VIS-NIR spectrometer, their microstructure and surface morphology was examined by scanning electron (SEM) and high resolution transmission (HRTEM) microscopies. Additionally, the microstructure homogeneity of the layers is examined by photoluminescence imaging using confocal microscopy. The solar cells parameters were obtained from I-V characteristics under ASTM conditions. Additionally the EQE and LBIC measurements are performed and analysed. One of the most important part of the work is characterisation the stability of the different kind of perovskite with and without the protective coatings. This work was supported by the Polish National Science Centre under the grant No. DEC-2012/05/B/ST8/00087.

Authors : Cheng-Tien Chu 1, Tzung-Fang Guo 2, Yao-Jane Hsu 3, Ten-Chin Wen 1*
Affiliations : 1Department of Chemical Engineering,2 Department of Photonics, National Cheng Kung University, Tainan 70101, Taiwan 3National Synchrotron Radiation Research Center, Hsinchu Science Park, Hsinchu, Taiwan

Resume : The performance of one-step CH3NH3PbI3 (MAPbI3) perovskite (PV) solar cells (SCs) is improved with 4-carboxy-phenyl-ammonium chloride (CPAC) as an additive. Generally, the one-step fabricated MAPbI3 thin films suffer from the defects due to the high rate of crystallization. It deteriorates the performance of MAPbI3 PVSCs. Herein, we demonstrate that CPAC can improve the film morphology of MAPbI3 and the power conversion efficiency (PCE) of the planar PVSCs (from 0.32% to 10.67%). The top-view SEM images show that the underlying substrate is fully covered by the continuous film of MAPbI3 with CPAC while it is partially covered by the needle-like crystals of pristine MAPbI3. Due to the improved surface coverage, the PV film with CPAC shows stronger absorption than the pristine PV in the UV-vis region from 300 to 600 nm. The XDR results verify that the additive of CPAC can enhance the crystallinity of the PV films. To fabricate the devices, the precursor solutions with MAPbI3 and CPAC (molar ratio = 1:0.3) was spin-coated atop the PEDOT:PSS layer and then annealed at 100℃ for 90 seconds. The average PCE for the planar PVSCs without any additive and the devicves with CPAC (device-Additive) are 0.23% and 9.93%, respectively. The best PCE for device-Additive is 10.67%. This work demonstrates that CPAC can dramatically improve not only the morphology but also the crystallinity of the MAPbI3 films and works as an effective additive to increase the performance of planar MAPbI3 PVSCs.

Authors : Pantea Aurang, Doga Doganay, Sahin Coskun, Firat Es, Rasit Turan, Husnu Emrah Unalan
Affiliations : Micro and Nanotechnology Department, METU, Ankara 06800, Turkey ; Department of Metallurgical and Materials Engineering, METU, Ankara 06800, Turkey ; Center for Solar Energy Research and Applications (GUNAM), METU, Ankara 06800, Turkey ; Department of Physics, METU, Ankara 06800, Turkey

Resume : Crystalline silicon (Si) solar cells have dominated photovoltaic market primarily due to abundant material supply. In recent years, much effort has been spent to decrease Si solar cell manufacturing costs and increase efficiency. In conventional cells, deposition of top contacts is achieved by screen-printing. Metal top contacts with minimum shading effect and low resistance are desired to improve the efficiency of the solar cells. One approach to eliminate this shading effect might be the use of transparent and conducting electrodes. Metal nanowire networks that are simply deposited through solution-based methods are promising candidates for transparent and conducting electrodes. Moreover, they can provide a medium for plasmonic scattering leading to an effective coupling of incident solar radiation into the solar cell. In this work, the potential of silver nanowire (Ag NW) networks as transparent top electrodes in single crystalline Si solar cells was investigated. Through the optimization of the optoelectronic properties of Ag NW networks and application of a post-deposition treatment for the formation of the ohmic contact at Ag NWs/Si interface, a relative enhancement in conversion efficiency of 21% was obtained when compared to the reference cells. This increase in the conversion efficiency was attributed to the higher charge collection probability within the nanowire contacts as opposed to the reference cells, where the large distance between metal fingers lowers the collection efficiency. In addition, the localized surface plasmon resonances of the Ag NWs could provide another significant contribution to the observed enhancement.

Authors : Bowon Yoo, Irene Sanchez-Molina and Saif A. Haque
Affiliations : Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom

Resume : Nowadays, solar cells employing organic-inorganic hybrid lead perovskites, APbX3, are one of the most attractive alternatives to the previous solar cells showing the efficiency spur from 3.8 % to 20.1 % in five years. However, the toxicity and instability of lead are vital problems to be solved. In order to replace lead, the main reason for the toxicity, tin based perovskite has been suggested for PV application in several papers, as a light absorber in a meso-superstructured solar cells and as a dye sensitiser in dye-sensitised solar cells showing prospective efficiency. Nevertheless, the stability of tin perovskite is worse than lead perovskite because Sn2+ gets easily oxidised to Sn4+ and therefore, ASnX3 is oxidized to A2SnX6 resulting in a drop in performance. Hence, finding different perovskite-based replacements for the lead perovskite could be one of solutions to address concerns, the toxicity and instability. In this poster we will present some of our results and progress on developing air-stable and non-toxic perovsite absorber materials focusing on tin and bismuth based materials. In particular, we will report the synthesis and characterization of such materials (optical and structural properties). We will also present results from laser based transient optical spectroscopy studies addressing interfacial charge separation dynamics and yields in photoactive layers comprising hole transporting materials and the perovskite absorber.

Authors : G.A. Nemnes1,2, S. Iftimie1, A. Palici1, A. Nicolaev1, A. Radu1, S. Antohe1,3
Affiliations : 1University of Bucharest, Faculty of Physics, Bucharest, Romania; 2Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering (IFIN-HH), Magurele, Romania; 3Academy of Romanian Scientists, Bucharest, Romania

Resume : Photovoltaic cells based on P3HT regio-regular polymer and ICBA fullerene derivative thin films were fabricated onto optical glass substrates covered with indium tin oxide (ITO). The active layer was customized as P3HT/P3HT:ICBA/ICBA sequence using organic solvents with different boiling points. Electrical and photoelectrical measurements were performed in dark and solar simulator conditions, at room temperature. Photovoltaic parameters, external quantum efficiency (EQE), short-circuit current (ISC), open circuit voltage (VOC) and fill factor (FF), were determined and compared with results obtained for P3HT:ICBA (1:1, wt. %) active layer structures. P3HT/P3HT:ICBA/ICBA structures provide a significant enlargement of photovoltaic response. The experimental results are complemented by numerical simulations for charge transfer at the interface and collection to the electrodes, using a lattice-gas type model. We investigate in how far the optimization of the interface in the active layer enhances the overall solar cell efficiency. Keywords: P3HT, ICBA, photovoltaic, interface optimization Acknowledgements: This work was partially supported by Romanian Executive Unit for Financing Higher Education, Research and Innovation (UEFISCDI) under SEE program, grant no. 8/2014

Authors : A. Jouane(1), F. Lmai(3), H. Jaouani(4), H. Ennamiri(4), D. Saifaoui(4), R. Moubah(1), Y. Jouane(2) and H. Lassri(1).
Affiliations : 1) LPMMAT, Faculté des Sciences Ain Chock, Université Hassan II, BP 5366 Mâarif, Casablanca, Morocco. 2)Department of Optoelectronic Engineering, School of Systems Engineering, Kochi University of Technology, 185 Miyanoguchi Tosayamada, Kami Kochi, 782-8502 Japan. 3)LPTA, Faculté des Sciences Ain Chock, Université Hassan II, BP 5366 Mâarif, Casablanca, Morocco. 4)Higher School of Textile and Clothing Industries, Laboratory REMTEX, Casablanca, Morocco

Resume : Titanium oxide possesses unique properties such as optical transparency, large band gap (3.3 eV), and good electron mobility. TiOx is one of the most important functional materials for a wide variety of photovoltaic devices. On the other hand, the sputtering technique is suitable to deposit high quality homogeneous TiOx thin films on large-areas, with a good reproducibility. Generally, the TiOx is deposited at low temperature following by thermal annealing treatment, which allows the highest control of film structure and morphology, as well as leading to significantly improved device efficiency and stability. Furthermore, we use a barrier layer of TiOx, which has always been considered a selective barrier layer with a low valence band (7.4 eV) and has been known to be an effective barrier for Polymeric modulators and inverted organic photovoltaic. Therefore, the role of TiOx as interfacial layer is to reduce the hole injection and remove the accumulated space charge for OLED or as blocking layer for OPV, thereby improving the efficiency in electronic devices. The electronic properties of TiOx suggest that it should be a suitable interlayer for collecting electrons at the ITO/TiOx bottom electrode. The valence band level of TiOx is located at −4.4 eV, [1] which suggests that electrons from LUMO of PCBM (−4.3 eV [2]) can be injected into the TiOx, while the holes from the semiconductor blend levels can be effectively blocked the conduction band level of TiOx, as reported by Kim et al. (−7.5 eV [1]. In this work we use RF magnetron sputtering to grow TiOx thin films with various thicknesses at different temperatures on ITO/Glass. The influences of the deposition temperature and film thickness (from 25 nm to 150 nm) on the crystalline and optical properties of the TiOx and active organic layer, as well as on the photovoltaic properties are investigated. The structural and electric analyzes carried out on the 50 nm a thick TiOx thin film deposited at room temperature on the ITO point out a strong correlation between TiOx crystallinity and photovoltaic performances. This sample presents improved photovoltaic properties and stability at room temperature. Indeed, the TiOx film shows a sharp absorption in the UV-visible curve characteristic of the TiOx band gap. The photoluminescence intensity of P3HT was totally quenched in the P3HT:PCBM thin film while there was no photoluminescence quench in the TiOx/P3HT double layer thin film. The influence of the growth conditions on the photovoltaic performance is still under investigation and will be discussed.

Authors : Kamalakannan Ranganathan 1,2, *, Boitumelo Matsoso 1, Bridget Mutuma 1, Daniel Wamwangi 2, Neil Coville 1
Affiliations : 1DST-NRF Centre of Strong Materials and the Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Johannesburg, South Africa, 2193; 2DST-NRF Centre of Strong Materials, School of Physics, University of the Witwatersrand, Johannesburg, South Africa, 2193

Resume : Photon harvesting in an organic photovoltaic (OPV) solar cells is a promising technology for future energy requirements. One of the key strategies to photon harnessing is the incorporation of graphene oxide (GO) as an independent hole transport layer (HTL) layer or with PEDOT:PSS [1,2]. However, GO has a large energy band gap and poor stability upon continuous light exposure, which limits device applications. In the present study, GO has been decorated with Ag nanoparticles (Ag-GO) and mixed with PEDOT:PSS for as a HTL. The Ag-GO exhibited a plasmonic Ag absorption at solar spectrum with reduced-GO properties which enhanced the light absorption in the visible range and hole collection efficiency of the HTL. The dark current analysis from space charge model revealed that Ag-GO addition in PEDOT: PSS increased the hole mobility by 58%. The 1 sun light illumination of the ITO/Ag-GO-PEDOT:PSS/PCBM:P3HT/Al device exhibited an enhanced short circuit current (Jsc) and photo conversion efficiency (PCE) by 126% and 100%, respectively. The device performance was analyzed by transport properties and cyclic voltammetry. Our results were establish the formation and existence of the new energy levels upon Ag-GO incorporation in PEDOT:PSS to enhances the charge transport between HTL and the ITO electrode. Keywords: Organic photovoltaic, Ag Nanoparticles, graphene oxide. Reference: 1. J. Liu et al., Energy Env. Sci 2014, 7, 1297–1306 2. X. Wu et al., J. mat. chem C, 2015, 2, 4044-4050

Authors : Yifan Dong; Irene Sanchez-Molina; Saif Haque
Affiliations : Department of Chemistry; Imperial College London

Resume : Perovskite materials such as methylammonium lead triiodide have emerged to be a promising candidate as an efficient light harvester in solar cells. The best efficiency of a perovskite solar cell has achieved 20.1%. However, the toxicity of lead and the degradation under ambient conditions have to be solved before commercialization. Recently we have shown that MAPbI3 film can undergo rapid degradation when exposed to light and molecular oxygen. More specifically, it was shown that the degradation of MAPbI3 (under light and in the presence of oxygen) is due to the superoxide (O2-) species that is generated through electron transfer from the perovskite to oxygen; here oxygen functioning as an electron acceptor. It was proposed that if a good electron extraction interlayer is introduced within the photoactive layer to extract the electrons efficiently, the yield of superoxide species is lowered.1 This in turn may serve to improve the stability of MAPbI3 under oxygen and light. This poster presents the effect of different electron transport layers on reducing the severity of the degradation pathway under oxygen and light. In particular, we will explore the use of compact and mesoporous tin oxide (SnO2) as well as doped metal oxide electron extractors as replacements for the commonly used TiO2 material. Steady-state and time-resolved photoluminescence (PL) and transient absorption spectroscopy (TAS) are carried out to investigate the yields of superoxide formation and interfacial charge transfer. These studies will be complimented by device fabrication and characterization of performance. References: 1 N. Aristidou, I. Sanchez-Molina, T. Chotchuangchutchaval, M. Brown, L. Martinez, T. Rath and S. A. Haque, Angew. Chem. Int. Ed. Engl., 2015, 54, 1–6.

Authors : M. Guc1, P. Fuchs2, F. Tsin3,4, J. Rousset3,4, Y.E. Romanyuk2, A. Pérez-Rodríguez1,5, V. Izquerdo-Roca1
Affiliations : 1Catalonia Institute for Energy Research (IREC), C. Jardins de les Dones de Negre 1, 08930 Sant Adrià del Besòs, Barcelona, Spain 2Empa – Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Thin Films and Photovoltaics, 8600 Dübendorf, Switzerland 3EDF R&D, 6 quai Watier, 78400 Chatou Cedex, France 4IRDEP, Institute of Research and Development on Photovoltaic Energy,UMR7174 CNRS EDF Chimie ParisTech, 6 quai Watier, 78400 Chatou Cedex, France, 5IN2UB, Departament d’Electrònica, Universitat de Barcelona, C. Martí i Franquès 1, 08028 Barcelona, Spain

Resume : This work reports a Raman scattering analysis of doped ZnO layers grown by different techniques (including Al-doped ZnO grown by sputtering and chemical bath deposition (CBD) [1], and electrodeposited Cl-doped ZnO [2]. Sputtered doped ZnO layers are widely used as transparent conductive oxide (TCO) windows in advanced chalcogenide thin film solar cells. Recently, solution-processed ZnO layers have been developed as alternative window layers in solar cells [1,2]. Raman scattering has a high potential for the non-destructive structural and electrical assessment of the processed ZnO layers. However, the full exploitation of the capabilities of Raman scattering based methods for the non-destructive assessment of these processes requires a deeper knowledge of their vibrational properties. In this context, we have developed a detailed comparative Raman scattering study that has been performed under resonant and non-resonant excitation conditions. The differences in the Raman spectra have been analyzed in relation to different structural properties of the processed layers and doping level. Additionally, the impact of different post deposition treatments on the processed layers has been analyzed. The challenges and limitations of Raman scattering based methods for the no destructive assessment of these processes will be discussed. [1] H. Hagendorfer et al., Adv. Mater. 2014, 26, 632–636. [2] J. Rousset et al. Chem. Mater. 2009, 21, 534-540.

Authors : Joe Briscoe,(1) Soosaimanickam Ananthakumar,(2) Xuan Li,(1) Ann-Louise Anderson,(1) Pelin Yilmaz,(1) Steve Dunn,(1) and Sridharan Moorthy Babu(2)
Affiliations : 1 Materials Research Institute, Queen Mary University of London, UK; 2 Crystal Growth Centre, Anna University, Chennai, India

Resume : There is growing interest to find a replacement for platinum as a counter electrode in dye sensitised solar cells (DSSCs), using earth-abundant elements to reduce the cost and allow high-volume production. These include a wide range of carbon-based materials, nitrides, sulphides and oxides. Here Cu2SnSe3 nanoparticles are synthesised using oleylamine as both a solvent and capping agent and spray coated onto conductive glass substrates to form DSSC counter electrodes using earth-abundant elements. The film requires annealing at only 400 °C in nitrogen, which is a lower temperature than previous reports of nanoparticle-derived films of both Cu2SnSe3 and Cu2ZnSnSe4, as well as avoiding the use of Se gas in the annealing process. The use of the weakly bound oleylamine as a capping molecule can account for this low annealing temperature, as thermogravimetric analysis shows that it is largely lost by 400 °C. The composition and phase of the material is confirmed to be close-to-stoichiometric Cu2SnSe3 by energy-dispersive X-ray spectroscopy, X-ray diffraction and Raman analysis. DSSCs using Cu2SnSe3 counter electrodes give a power conversion efficiency of 4.87 %, compared to 5.35 % when using a Pt counter electrode. Significantly, electrochemical impedance spectroscopy indicates that the performance of the Cu2SnSe3 electrode is enhanced under illumination, leading to a drop in the charge transfer resistance to levels comparable to Pt. This is attributed to absorption of light in the Cu2SnSe3 counter electrode leading to a higher overpotential of photoexcited carriers and therefore a higher catalytic activity. The narrow band gap (0.4-0.9 eV) of this material means that such super band gap light is able to penetrate through the dye layer. This novel mechanism for the enhancement of counter electrode performance may be found in a number of other semiconducting counter electrodes and is therefore important to consider when developing effective earth-abundant counter electrodes in the future.

Authors : Maciej Klein 1;2, Mariusz Szkoda 3, Katarzyna Siuzdak 2, Jakub Karczewski 1
Affiliations : 1 Faculty of Applied Physics and Mathematics, Gdansk University of Technology, Narutowicza 11/12, 80-233 Gdansk, Poland; 2 Centre for Plasma and Laser Engineering The Szewalski Institute of Fluid-Flow Machinery, Polish Academy of Science Fiszera 14, 80-231 Gdansk, Poland; 3 Department of Chemistry and Technology of Functional Materials Chemical Faculty, Gdansk University of Technology, Narutowicza 11/12, 80-233 Gdansk, Poland

Resume : Dye-sensitized solar cells (DSSC) are promising candidates for the development of low-cost third-generation photovoltaic devices. Remarkable power-conversion efficiency of over 14% was reached for a prototype DSSC, paving the way for their commercialization. However, for some applications such as architectural integration of solar cells in the form of colorful windows on the building facade, the semitransparent photoanodes are highly desired. In this work we show formation and characterization of semi-transparent ordered TiO2 nanotubes prepared by one-step anodization process of 1.5 μm–thick titania layer deposited onto the semitransparent glass via magnetron sputtering. As a conductive and semitransparent substrate, FTO covered with thin titania film was used. Obtained nanotubes were characterized by SEM, UV-vis spectroscopy and Raman spectroscopy. Prepared electrodes were used as a photoanode for DSSCs construction. To improve the photoconversion efficiency TiO2 nanotubes were decorated by the TiO2 nanoparticles. Current-voltage characteristics as well as calculation of electrical parameters of solar cells were carried out. This work was supported by the Polish Ministry of Science and Higher Education under “Diamond Grant” 0228/DIA/2013/42 and Polish National Science Centre under grant 2012/07/D/ST5/02269.

Authors : A. Laskarakis1, A. Zachariadis1, V. Matskos2, V. Larat3, M.Stchakovsky2, J.-P. Gaston4, S. Kashiwagi3, M. Sallami4, S. Logothetidis1
Affiliations : (1) Lab for Thin Films - Nanobiomaterials, Nanosystems & Nanometrology (LTFN) Dept Physics, Aristotle University of Thessaloniki 54124 Thessaloniki, Greece; (2) Organic Electronic Technologies P.C. (OET), Antoni Tritsi 21B, 57001 Thessaloniki, Greece; (3) Horiba Scientific, Villeneuve d’Ascq, France; (4) Horiba Scientific, Palaiseau, France

Resume : Organic Electronics (OE) is a rapidly emerging field that is expected to revolutionize conventional electronics, energy and photonic applications. Some of the most important OE applications include Organic Photovoltaic (OPV), e-paper, Organic Light Emitting Devices (OLED) for displays & lighting and sensors. For cost efficiency reasons, the processing of these devices is targeted on large surfaces roll to roll (R2R) machines. For the most mature applications, the trend is to enhance processing areas, speeds and reduce feature sizes. For less mature ones, the efforts are still made to fully understand growth of nanomaterials. In both cases, optical probes are employed to characterize or monitor the properties of the materials used. In this work, we report on the innovative integration of in-line Spectroscopic Ellipsometry and Raman Spectroscopy in R2R pilot line for the robust characterization and modelling of the thickness and optical properties of nanomaterials and devices for OPVs. This has been developed in the framework of the EU funded project Smartonics (2013 - 2017), which aims at developing pilot lines that will combine smart technologies with smart nanomaterials for the precision synthesis of Organic Electronic (OE) devices.

Authors : M. Bedoui, M. M. Habchi*, K. Chakir, I. Moussa, A. Rebey, B. El Jani
Affiliations : University of Monastir, Faculty of Sciences, Unité de Recherche sur les Hétéro-Epitaxies et Applications, 5019 Monastir, Tunisia

Resume : InxGa1-xAs/GaAs structures, grown by metalorganic vapor phase epitaxy (MOVPE) at 520°C, were investigated by in situ spectral reflectance (SR), high resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM). HRXRD curves are analyzed to determine the indium composition of different samples, denoted A, B, C, D and E. Reflectance three-dimensional plot as function of time and wavelength was recorded to quantify the evolution of reflectivity in the wavelength range from 400 to 1000 nm and to determine some growth parameters such us growth rates and thicknesses of InxGa1-xAs layers. Longitudinal cut through the 3D plot shows dissimilar behavior of reflectivity temporal evolution in three regions: region I (400-560 nm), region II (560-750 nm) and region III (750-1000 nm). Best simulations of reflectivity signals using the transfer matrix method (TMM) are developed to analysis the variation of optical constants spectra and the sensitivity (σSR) of incident wavelength to surface morphology of InxGa1-xAs layers. The obtained values of σSR were compared to RMS surface roughness given by AFM. A good agreement between the experimental results and the theoretical predictions was found. Keywords: InxGa1-xAs/GaAs structures; In situ spectral reflectance; refractive index; Atomic force microscopy; MOVPE. *Corresponding Author:

Authors : Nicola Sestu, Michele Cadelano, Valerio Sarritzu, Feipeng Chen, Daniela Marongiu, Roberto Piras, Marina Mainas, Francesco Quochi, Michele Saba, Andrea Mura, Giovanni Bongiovanni
Affiliations : Dipartimento di Fisica, Università degli Studi di Cagliari, I-09042 Monserrato, Italy

Resume : Advances in optoelectronic devices based on methylammonium lead halide perovskites depend on understanding the role of excitons, whether it is marginal as in inorganic semiconductors, or crucial, like in organics. However, a consensus has not been reached on the value of the exciton binding energy and its temperature dependence, not even on the most widely studied materials, such as methylammonium lead iodide (MAPbI3) and methylammonium lead bromide (MAPbBr3). The customary methods to estimate the exciton binding energy are rather ambiguous. As a consequence, widely spread values for the binding energy have been reported, e.g., in MAPbI3 ranging from 2 to 50 meV. Uncertainty reigns also over the temperature dependence of the exciton binding energy. Here we present an analysis of the UV-Vis absorption spectra of perovskite materials based on an f-sum rule on the integrated absorption, leading to the unequivocal determination of the exciton binding energy. Unlike standard methods, it only depends on parameters that can be readily extracted from the experimental data,without the ambiguities of fitting procedures. In the temperature range 80-300 K, we find that the exciton binding energy in MAPbBr3 is EB = (60 ± 3) meV, independent of temperature; for MAPbI3, in the orthorhombic phase (below 140 K) EB = (34 ± 3) meV, while in the tetragonal phase the binding energy softens to 29 meV at 170 K and stays constant up to 300 K.

Authors : B. Slimi (a,b), M. Mollar (a), I. Ben Assaker (b), A. Kriaa (c), R. Chtourou (b), B. Marí (a)
Affiliations : (a) Institut de Disseny i Fabricació, Universitat Politècnica de València, Camí de Vera s/n 46022-Valencia, Spain (b) Laboratoire Photovoltaïques, Centre de Recherches et des Technologies de l’Energie Technopole BorjCedria, Bp 95, Hammam Lif 2050, Tunisie (c) Laboratoire de Chimie Moléculaire Organique, 5 Avenue TahaHousseinMonfleury, 1089 Tunis, Tunisie

Resume : The new class of solar cells based on perovskite absorbersare solution-processable, cheap and use only earth-abundant materials, making them a prime contender for high efficiency, low-cost solar power generation. In our study, stable organic-inorganic hybrid perovskite NH2CHNH2PbI3 phase (FAPbI3) thin films was synthesized a coating method by centrifugation in a single step on a substrate of ITO, with a study on the effect of the annealing temperature. FAPbI3 thin films obtained were characterized by FESEM, X-ray diffraction, UV-Vis spectroscopy and photoluminescence. FESEM analysis showed homogeneous perovskite layers. EDX analysis showed that themolar ratio was 75% and 25% for iodide and lead, respectively. XRD analysis for the deposited films on ITO with treats up to 140 ° C the phase γ-FAPbI3 majority and with the presence of a peak was 12.6 ° matches at PbI2. As for recent movies at 150 ° C there is the cubic phase α-FAPbI3 with the space group of Pm-3m. From 160 ° C γ-FAPbI3 phase is removed, but increased PbI2 peak intensity which leads to a perovskite decomposition. At this stage there is a defined absorption edge at 810 nm (1.52eV) in the UV-Vis spectrum, accompanied by a PL peak at 810 nm under optical excitation with monochromatic laser light.

Authors : Marianna Raappana, Ville Polojärvi, Timo Aho, Arto Aho, Antti Tukiainen, Lauri Hytönen, Riku Isoaho, Mircea Guina
Affiliations : Optoelectronics Research Centre, Tampere University of Technology, FIN-33101 Tampere, Finland

Resume : Dilute nitride compounds (GaInNAsSb) have gained increased attention due to their unique material properties which are beneficial for high-efficiency solar cells. While the efforts have largely focused on epitaxy optimization, other aspects should also be considered when optimizing device processing, in particular mesa fabrication. Here, we report wet etching of GaInNAs, GaInNAsSb, and GaNAsSb solar cell materials using three different compositions of HCl:H2O2:H2O solution. Samples were studied using stylus profilometry, atomic force microscopy, and scanning electron microscopy. The 1:1:2 solution created rough surfaces with directional faceted grooves in the [011] direction. The corresponding etch rate was ~0.5 µm/min and showed no dependence on the In and Sb compositions. The 1:10:40 solution resulted in smoother but granular surfaces and faceted mesa sidewalls. This etchant also provided the fastest etch rates while clear dependence between material composition and etch rate was revealed; the etch rate increased with higher Sb composition. The 10:1:4 solution had the slowest etch rates while producing rounded mesa sidewalls and smooth surfaces with root-mean-square roughness values of <0.3 nm. Finally, HCl-based solution was used for etching mesa structures on triple-junction solar cells containing dilute nitride bottom junctions. Good electrical characteristics of the solar cells validate the choice of HCl-based etchant for the mesa fabrication.

Authors : A. Gonzalo (1), A.D. Utrilla (1), D.F. Reyes (2), V. Braza-Blanco (2), D. Fuertes Marrón (3), T. Ben (2), D. González (2), A. Guzman (1), A. Hierro (1), J.M. Ulloa (1).
Affiliations : (1) Institute for Systems based on Optoelectronics and Microtechnology (ISOM), Universidad Politécnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain. (2) Departamento de Ciencia de los Materiales e IM y QI, Universidad de Cádiz, 11510 Puerto Real (Cádiz), Spain. (3) Instituto de Energía Solar, Universidad Politécnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain.

Resume : Multi-junction solar cells (SCs) hold the record conversion efficiency over all other PV-technologies for 20 years and the theory predicts that 1eV bandgap layers lattice-matched to GaAs/Ge would still provide a significant improvement. A recent approach is by means of GaAsSbN, which allows combining independent tuning of conduction and valence bands with strain engineering. However, the achievement of high quality GaAsSbN layers faces important challenges inherent to the growth of highly mismatched diluted nitrides. These problems could be solved by substituting thick layers by nanostructures such as type-II GaAsSb-GaAsN superlattices (SL) spatially separating Sb and N atoms, which could offer additional advantages such as long carrier lifetime and, therefore, enhanced collection efficiency. Our study focuses on strain-balanced GaAs(Sb)(N)-based type-I and type-II SLs grown on GaAs by MBE. We analyze the impact of composition and period thickness on the SL properties and make a comparison with equivalent bulk layers. Based on high resolution X-ray diffraction and transmission electron microscopy, along with photoluminescence and photoreflectance, we find that type-II SL structures provide better control over composition and lattice-matching as compared to either type-I or thick-layer alternatives. Additionally, SC devices processed from p-i-n SL structures show high photocurrents compared with reference GaAs SCs. Performance under AM1.5 conditions will be also analyzed.

Authors : K. Chakir, C. Bilel, M.M. Habchi, A. Rebey, and B. El Jani
Affiliations : University of Monastir, Faculty of Sciences, Unité de Recherche sur les Hétéro–Epitaxies et Applications, 5019 Monastir, Tunisia

Resume : The dependence of carrier effective mass of GaNxAs1-x, InNxP1-x, InNxAs1-x, and InNxSb1-x alloys on nitrogen content is theoretically investigated using a 10-band k.p model. The electron effective mass m*e at the bottom of conduction band in GaNxAs1-x and InNxP1-x exhibits a gradual increase as a function of N concentration in the range 0-1% and a decrease for x between 1 and 5 %. However, the behavior of m*e in InNxAs1-x and InNxSb1-x shows a strongly decrease in all studied x-range. Our theoretical results are compared with the available data reported in the literature. On the other hand, contrary to heavy-hole effective mass m*hh, the light-hole effective mass m*lh in all studied alloys is significantly affected by nitrogen states which modify the non-parabolicity of the LH band. The modification of the carrier effective mass affects the transport and mobility properties of the III-N-V alloys. Keywords: Diluted III-N-V alloys; 10-band k.p model; carrier effective mass. * Corresponding author:

Authors : R. Boussaha, K. Chakir, H. Fitouri, A. Rebey and B. El Jani
Affiliations : University of Monastir, Faculty of Sciences, Unité de Recherche sur les Hétéro-Epitaxies et Applications, 5019 Tunisia.

Resume : InAsBi layers were elaborated on semi-insulating (100) GaAs substrates misoriented10° by atmospheric pressure metalorganic vapor phase epitaxy (MOVPE) reactor. Spectral reflectance in the range of 200 to 1100 nm was employed to in situ monitor epitaxy. For determining the optical constants of InAsBi films, an optical model incorporating time-dependent surface roughness and time-dependent growth rate was used to simulate the in situ reflectance. A theoretical motivation for the introduction of these two parameters instead of a standard single rms roughness and growth rate is provided Several InAsBi samples grown at different growth temperatures were used to illustrate ways in which the parameters introduced can be evaluated. Reflectivity analysis was ex situ correlated by atomic force microscopy. Keywords: InAsBi, In situ spectral reflectance, optical model, refractive index Corresponding authors:,

Authors : Hasan Huseyin Gullu1-2, Ozge Bayrakli1-2, Emre Coskun3, Mehmet Parlak1-2
Affiliations : 1. Department of Physics, Middle East Technical University (METU), Ankara 06800, Turkey 2. Center for Solar Energy Research and Applications (GÜNAM), METU, Ankara 06800, Turkey 3. Department of Physics, Canakkale Onsekiz Mart University, Canakkale 17100, Turkey

Resume : ZnSe structure belongs to the family of the II–VI compound semiconductor materials and has a 2.67 eV direct band gap. This structure attracts interests as to be a promising material for different optoelectronic devices such as LEDs, thin film transistors, photodetectors, and thin-film solar cells. In this work, heterojunction of In/n-ZnSe/p-Si/Al fabricated by physical vapor deposition system at the substrate temperature of 200°C was characterized in consideration of the previous work on the material characterization of ZnSe thin films [1]. In this previous work, the ZnSe film samples were prepared on the ultrasonically cleaned soda-lime glass substrates under the same deposition conditions. The structural and optical characteristics of these films were reported depending on the post thermal annealing process applied in the 300-500°C temperature range [1]. Mainly, ZnSe samples were found in polycrystalline zinc-blende structure at (111) preferred orientation direction and the fundamental optical band gap energy of them was found about 2.7 eV. In order to determine the device parameters and transport properties of n-ZnSe/p-Si heterojunction, temperature-dependent I-V measurements were carried out in the temperature range of 220–360 K. The series resistance and shunt resistance values were calculated by the help of the parasitic resistance relation for forward and reverse voltages. This p-n junction showed a very good diode behavior with the rectification factor of about 10^5 at 1.0 V in dark condition. The ideality factor and the barrier height values of the heterojunction diode were determined by performing different I–V plots. In addition, spectral photoresponse analysis was studied in order to observe the contribution of the p- and n-layer in the junction. [1] H.H. Güllü, E. Coşkun, M. Parlak, “Investigation of optical parameters of thermally evaporated ZnSe thin films”, Phys. Status Solidi C, 12 (2015) 1224-1228

Authors : Milivoj Plodinec(a), Andreja Gajovi?(a), Irena Kerekovi?(a), Vilko Mandi?(a), Krunoslav Jurai?(a), Daniel Meljanec(a), Miran ?eh(a), Davor Gracin(b)
Affiliations : (a)Ru?er Bo?kovi? Institute, Bijeni?ka 54, HR-10002 Zagreb, Croatia; (b)Jo?ef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia;Ru?er Bo?kovi? Institute, Bijeni?ka 54, HR-10002 Zagreb, Croatia

Resume : TiO2 is known as material with excellent chemical and photochemical stability. It exists in three different crystalline phases: anatase, rutile and brookite. It was found that anatase is photocatalytically more active than rutile due to its large surface area. This activity depends not only on the phase of TiO2 but also on the crystallite size and porosity. The morphology parameters, e.g., nanotube length, diameter, smoothness, depend on the anodization conditions, such as voltage, electrolyte composition, temperature, and duration. After anodization, the amorphous nanotubes can be annealed to increase the electron mobility, sensitized with dyes or polymers to increase solar photon absorption, and doped or surface-functionalized to adjust the density of states1. On the other hand, perovskite type of solar cells are one of the hottest prospects in clean energy research, offering good power outputs from low-cost materials that are relatively simple to process into working devices. Perovskite solar cells based on organometal halides represent an emerging photovoltaic technology. Perovskite solar cells stem from dye-sensitized solar cells. In 2009 was reported the first developed perovskite based solar cell structure with conversion effieciency of 3-4%, and up to now increase to 20.1 %2. Lately we focus our research on investigation of the synthesis uniform and higly ordered TiO2 arrays nanotubes at different transparent substrate (glass, ZnO/glass). The thin layers of Ti film will be obtained by vapor deposition and magnetron sputtering. Also, the both oxides, ZnO and TiO2 will be used to form nanocomposite. In that way, the nanostructure of one material coupled with another material form a composite in the nanoscale resulting in variety of properties different from the original material that enable tuning its property as desired. The main aim of these project will be to deposited the perovskite materials into different pore size and different length of TiO2 nanotube arrays at different substrate. We will study how the different size properties of nanotubes and perovskite crystals size influence on the efficiency of solar cells. By changing the size of perovskite crystals is possible tune the maximum of absorbance in the desired region of solar irradiation. The all prepared samples will be studied by HRSEM, HRTEM, Raman spectroscopy, Impendance spectroscopy, UV-Vis-NiR spectroscopy. It will be discussed different way of preparation TiO2 nanotube arrays and dimensions on optical properties and efficiency of solar cells. 1 K. Lee, A. Mazare, P. Schmuki, Chem. Rev., 2014, 114 (19), 9385?9454. 2 Nam-Gyu Park, materials today, 2015, 18(2), 65?72.

Authors : R. Gheriani1, R. Rehaiem1, A. Taabouche2, B. Benhaoua3
Affiliations : 1Laboratory of Radiation, Plasma and Surface Physics (LRPPS), Faculty of Mathematics and Sciences of matter University of Ouargla, 30000, Algeria. 2Laboratory of Thin Films and Interfaces (LCMI), University of Constantine, 25000, Algeria. 3Laboratory VTRS, University of El-Oued, 39000, Algeria.

Resume : NiO is an interesting p-type material that can be deposited by various techniques. We can find this material in several technologic applications such as electrode in solar cell, solar thermal absorber, catalyst for oxygen evolution, conductometric gas sensor and organic light emitting diodes. The aim of our work was the elaboration of NiO thin films on glass substrates (Ref: 217102) as transparent conducting oxide with low resistivity and high transmittance by choosing suitable preparation conditions using ultrasonic spray technique, for this we used nickel nitrate solutions (Ni-NO3) with different solutions: 0.05-0.1M). During deposition the substrates were kept heated at 500°C. Crystal structure and vibrational study were investigated by X-ray diffraction and micro-Raman spectroscopy, respectively. UV-Vis spectrophotometer was used to find the transmittance spectrum and energy band. XRD spectra showed that NiO films are formed and grow in a privileged orientation. UV–Vis investigation confirmed that the coatings are highly transparent with an average transmittance equal about 80%. From The Raman spectra we observed that the most intense vibrations of NiO are precisely: TO at 309 cm−1 and LO mode at 608 cm−1, three excitations at ~ 1096, ~1042 and ~986 cm−1 with very high intensity were detected. The relatively large peaks width of the NiO Raman modes in these thin films is in agreement with the reduced particle sizes. Thin films were investigated by scanning electron microscopy to observe their surface morphology. Keywords: Nickel oxide, X-ray diffraction UV-Vis, Micro-Raman spectroscopy, Optical properties.

Authors : Vilko Mandić, Davor Gracin, Andreja Gajović, Andrea Moguš-Milanković, Milivoj Plodinec, Daniel Meljanac, Irena Kereković, Krunoslav Juraić
Affiliations : Ruđer Bošković Institute, Bijenička cesta 54, HR-10000 Zagreb, Croatia

Resume : Majority of solar cells (SC) repose on transparent conductive layers (TCO). Overlaying charge transfer layers (CT) are concerned as critical ones for high efficiency dye-electrode electron transport. Layers roughness ensures active material can be thin enough to overcome the problem of low lifetime of photogenerated carriers; the optical gap and surface chemistry determine transfer of photo generated carriers towards the external circuit, while both influence the efficiency/stability of SC, especially organic. The most important task in multilayer SC is to ensure overall compatibility of active/passive layers, while the use of various nanostructural arrays may allow additional tuning. We prepared ZnO/TiO2 nanoarrays/nanotubes architectures as candidates for electron accepting/extracting layers in SC devices, using Ti anodization and magnetron ZnO deposition. Several of nanostructures were infiltrated with organic absorbers. The role of interfacial phenomena responsible for SC performance/stability was focused. Interfacial differences were evaluated using electron microscopy, photoluminescence spectroscopy on non-contacted samples revealed charge transfer mechanism, while photoinduced absorption gave information on excited states kinetics. Impedance spectroscopy in the dark and under illumination showed the role of dielectric properties and identified relevant time scales for electronic transport and recombination. Proposed TCO and CT layers are applicable for the SC assembly.

Authors : Hee-Sung Keum1, Si Woo Lee1, Min-Soo Choi2, Jang-Joo Kim2, Hyun Hwi Lee3,*, Hyo Jung Kim1,*
Affiliations : 1Department of Organic Material Science and Engineering, Pusan National University, Busan 46241, Korea; 2Department of Materials Science and Engineering and the Center for Organic Light Emitting Diode, Seoul National University, Seoul 08826, Korea; 3Pohang Accelerator Laboratory, POSTECH, Pohang 37673, Korea; e-mail to:,

Resume : We investigated the effects of annealing temperature as well as fullerene on the morphology of thin films, lattice parameters and strain in zinc phthalocyanine(ZnPc) systems for small molecular organic photovoltaics (SM-OPVs) using X-ray reflectivity and GIWAXS (Grazing Incident Wide Angle X-ray Scattering) measurements. Surface roughness of ZnPc/C60 thin films increased as annealing temperature increased, while surface roughness of ZnPc/C70 thin films was stable in the high temperature region as high as 180℃. The compressive strain of ZnPc layer was larger under the fullerene layer in comparison with the single ZnPc layer. In addition, the strain of ZnPc disappeared at 180℃ in the presence of C70. The surface morphology was affected by the different strain evolution and interface stability which were dependent on the fullerene types. As a results, the grain size of ZnPc/C60 was larger than the grain of ZnPc/C70, which corresponded to ~120 nm.

Authors : Wiria Soltanpoor1,3, Mehmet Cem Şahiner2,3, Selçuk Yerci1,2,3
Affiliations : 1 Department of Micro and Nanotechnology, Middle East Technical University, Ankara, 06800, Turkey; 2 Department of Electrical and Electronics Engineering, Middle East Technical University, Ankara, 06800, Turkey; 3 The Center for Solar Energy Research and Applications, Middle East Technical University, Ankara, 06800, Turkey;

Resume : Organic-inorganic perovskite materials have been introduced as the new class of low cost photovoltaic devices to have the promise to compete with current commercialized inorganic solar cells. Having a direct tunable band gap, perovskite strongly absorbs a broad range of solar spectrum demonstrating a useful inexpensive candidate for the absorber layer in heterojunction photovoltaic devices. Relatively long minority carrier lifetime and high carrier mobilities within perovskite have led to power conversion efficiencies of more than 20% recently. However, despite all the interesting optoelectronic properties, there are concerns to be addressed. Apart from the stability issue of perovskite, one of the biggest controversy regarding these materials is whether or not they can be made with large active areas and in turn larger scale productions. In this study, using thermal co-evaporation technique, we made highly crystalline and uniform perovskite layers with decent morphology that provides for high reproducibility and compatibility to large-area applications. The optimization of the deposition and annealing conditions that we present, such as the temperature of the substrate during the deposition and the atmosphere in which, the perovskite layer is annealed in-situ, has enhanced the crystallinity and the optoelectronic properties of the perovskite absorber in large areas. In addition, the effect of different electron and hole transport layers were investigated in order to improve the hetero-structure band alignment and consequently, raise the photovoltaic efficiencies.

Authors : Mihaela Girtan-1, George Mousdis-2, Mohammed Rasheed-1
Affiliations : 1-Photonics laboratory, LUNAM, Angers, University 2-National Hellenic Research Foundation, Theoretical and Physical Chemistry Institute-TPCI, 48 Vass. Constantinou Ave., Athens 11635, Greece

Resume : Recently the organic perovskites Methylammonium LeadIodide (CH3NH3PbI3), have been used as absorbers in photovoltaic solar cells, giving rise to a spectacular improvement of the photo-electric conversion efficiency from 3.8% in 2009 to a 21% in 2014. The yield and stability of the photovoltaic device is strongly depended from the quality of the film and the preparation method used. The most promising method is the spin coating method not only due to the quality of the devices produced but also due to its low cost and ability to be used for industrial production. The quality of the spin coated films depends from many factors like the quality of the 1st materials, the solvent, the steps, the speed, the annealing temperature etc. Here we report the synthesis of CH3NH3PbI3 nanowires with a mean diameter of 50 and 400 nm a length more than 200 μm by an easy spin-coating method on glass substrates. The one-dimensional form of MAPbI3 could have unique optical and electrical properties. The feasibility of anisotropic growth of organolead halide perovskites opens up a new strategy toward the realization of low-temperature, solution processed films with controlled morphology. The resulting films containing these nanowires were examined by by UV-Vis spectroscopy, XRD and SEM to find the effect of the preparation factors to the quality of the film.

Authors : (1,4) Silvia. L. Fernandes, (2) Anna C. Véron, (2) Frank A. Nüesch, (1) Maria Aparecida Zaghete, (3) Carlos Frederico de Oliveira Graeff
Affiliations : 1) UNESP- Instituto de Química de Araraquara- SP, Brazil; (2) Laboratory for Functional Polymers, Swiss Federal Laboratories for Materials Science and Technology (Empa), 8600 Dübendorf, Switzerland; (3) UNESP- Faculdade de Ciências de Bauru, Departamento de Física- SP, Brasil; (4) POSMAT- Programa de Pós Graduação em Ciência e Tecnologia dos Materiais, Bauru- SP.

Resume : Hybrid organo-metal halide perovskites are a new class of solar absorber materials that possess intense broad light absorption over the visible spectral range with a band gap of 1.55 eV (1). These materials offer an extraordinary potential in photovoltaic devices with efficiencies higher than 20% (2). Typical perovskite solar cells incorporate a compact TiO2 buffer layer on top of the fluorine-doped tin oxide (FTO) electrode. Its role is to prevent recombination of extracted electrons and holes. In this work we demonstrate the potential of Nb2O5 to replace the standard TiO2 buffer layer and studied the influence of the oxide layer on the performance of the devices. The devices were constructed as follow: FTO/ compact oxide (Nb2O5 or TiO2)/ mesoporous TiO2/ CH3NH3PbI3/ Spiro-OMeTAD/ Au. Solar cells fabricated using Nb2O5 layer reached more than 12% power conversion efficiency (PCE) with an open circuit voltage (Voc) of 0.9 V, a current density (Jsc) of 17 mA/cm2 and a fill factor (FF) of 75%. On the other hand, solar cells fabricated with TiO2 showed PCE of 11%, Voc of 0.8 and FF of 72%. The influence of the thickness of the oxide layer was studied. We found that the J-V hysteresis of the cells is strongly dependent on the layer thickness. Devices constructed with 50 nm Nb2O5 have no or only very small hysteresis, and the hysteresis increases with increasing Nb2O5 layer thickness. In addition, the use of Nb2O5 improved the stability of the devices under illumination.

Authors : (1,4) Silvia. L. Fernandes, (2) Anna C. Véron, (2) Frank A. Nüesch, (1) Maria Aparecida Zaghete, (3) Carlos Frederico de Oliveira Graeff
Affiliations : 1) UNESP- Instituto de Química de Araraquara- SP, Brazil; (2) Laboratory for Functional Polymers, Swiss Federal Laboratories for Materials Science and Technology (Empa), 8600 Dübendorf, Switzerland; (3) UNESP- Faculdade de Ciências de Bauru, Departamento de Física- SP, Brasil; (4) POSMAT- Programa de Pós Graduação em Ciência e Tecnologia dos Materiais, Bauru- SP.

Resume : Hybrid organo-metal halide perovskites are a new class of solar absorber materials that possess intense broad light absorption over the visible spectral range with a band gap of 1.55 eV (1). These materials offer an extraordinary potential in photovoltaic devices with efficiencies higher than 20% (2). Typical perovskite solar cells incorporate a compact TiO2 buffer layer on top of the fluorine-doped tin oxide (FTO) electrode. Its role is to prevent recombination of extracted electrons and holes. In this work we demonstrate the potential of Nb2O5 to replace the standard TiO2 buffer layer and studied the influence of the oxide layer on the performance of the devices. The devices were constructed as follow: FTO/ compact oxide (Nb2O5 or TiO2)/ mesoporous TiO2/ CH3NH3PbI3/ Spiro-OMeTAD/ Au. Solar cells fabricated using Nb2O5 layer reached more than 12% power conversion efficiency (PCE) with an open circuit voltage (Voc) of 0.9 V, a current density (Jsc) of 17 mA/cm2 and a fill factor (FF) of 75%. On the other hand, solar cells fabricated with TiO2 showed PCE of 11%, Voc of 0.8 and FF of 72%. The influence of the thickness of the oxide layer was studied. We found that the J-V hysteresis of the cells is strongly dependent on the layer thickness. Devices constructed with 50 nm Nb2O5 have no or only very small hysteresis, and the hysteresis increases with increasing Nb2O5 layer thickness. In addition, the use of Nb2O5 improved the stability of the devices under illumination.

Authors : Meilin LI, Stefan ADAMS
Affiliations : Solar Energy Research Institute of Singapore (SERIS), National University of Singapore, 7 Engineering Drive 1, E3A #06-01, Singapore 117574 & Department of Materials Science and Engineering, National University of Singapore, EA #03-09, 9 Engineering Drive 1, Singapore 117575

Resume : Fluorene-triphenylamine copolymers (e.g. poly(9,9’-di-n-oc-tylfluorenealt-N- (4-butylphenyl)-diphenyl-amine), TFB) have attracted significant attention as effective hole transporting materials (HTMs) in bulk heterojunction organic solar cells (OSCs), perovskite solar cells and organic light-emitting diodes (OLEDs). In this computational study, we focus on the combination of a model sulfonated fluorene-triarylamine copolymer anion poly((N-(4-butylphenyl)-diphenylamine)-alt-fluorene 9,9’di-n-propane sulfonate), BAFS, with a wide range of monovalent cations. Ionic aggregation due to the interaction between sulfonate groups and cations results in unique optoelectronic properties. Moreover, the performance of TFB as the HTM can in principle be tuned by controlling the ionic interactions, because the hole conductivity depends on ionic aggregation. Systematic Molecular Dynamics (MD) simulations of BAFS with various monovalent cations are conducted and the resulting trajectories are analyzed for each of the conjugated polyelectrolyte focusing on ion aggregation and its influence on the static and dynamic polymer morphology as well as on the charge carrier mobilities that are relevant for the use of such HTMs in OSCS and OLEDs. A pronounced variation of the degree of cation clustering with the cation field strength is found to control polymer morphology, cation mobility and thereby the time evolution of the Coulomb energy landscape for hole transport.

Authors : Meilin LI, Lee Loong WONG, Stefan ADAMS
Affiliations : Solar Energy Research Institute of Singapore (SERIS), National University of Singapore, 7 Engineering Drive 1, E3A #06-01, Singapore 117574 & Department of Materials Science and Engineering, National University of Singapore, EA #03-09, 9 Engineering Drive 1, Singapore 117575

Resume : Due to its excellent charge carrier mobility poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT) has been extensively studied as active layer in electronic devices, incl. donor-acceptor bilayer solar cells of F8BT with PFB (Poly(9,9?- di-n-octylfluorene-alt-bis-N-N?-(4-butylphenyl) bis-N,N?- phenyl- 1,4-Phenylenediamin)). An interfacial layer of F(NSO3)2 (Poly[(9,9?bis ((N-(4-sulfonate-1 -butyl)- N,N-dimethylammonium)-ethanyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)]) was reported to affect the energetics of the states controlling charge separation at the donor-acceptor interface, thus increasing open-circuit voltage, short-circuit current and fill factor. Here, we develop and validate coarse-grained forcefields for F8BT, PFB and F(NSO3)2 to reduce the computational cost during molecular dynamics simulations of interface effects. Coarse-graining simplifies the F8BT, PFB and F(NSO3)2 molecules, which leads to a considerable acceleration of simulations. Energy contributions describing the interactions between the beads in the coarse-grained forcefield are derived by identifying suitable functional forms and fitting the interaction parameters to the corresponding variation of energy terms in atomistic structure models using the validated COMPASS forcefield. The final coarse-grained forcefields allow for a nearly two orders of magnitude gain in computational efficiency when studying bulk and interface structures of PFB/F(NSO3)2/F8BT system with only minor loss in accuracy.

Authors : Yu-Han Chang, Juen-Kai Wang
Affiliations : Academia Sinica

Resume : Nowadays, in planar perovskite solar devices, a thin metal oxide film, is usually introduced as an electron transport layer. Among all of the electron transport layers used in planar perovskite devices, TiO2 is the most widely used and the most successful one. However, there are several disadvantages while using TiO2, for instance, the process temperature is high (>450°C), which increases the cost of the whole process and limits the choices of substrates. On the other hand, ZnO, is a good alternative choice for it has higher electron conductivity and low temperature fabrication. Though ZnO has been widely used in many other applications, yet only three groups applied it on perovskite solar devices by either using sputter, ALD, or sol-gel methods. However, the cost of sputtering process is expensive because of the target and also the sputtering rate is very slow. The same problems exist in ALD. Sol-gel is a non one-step process and makes poor ZnO/Perovskite interface. In this study, to solve the interface problems, we took the advantage of microwave process’s unique characteristics, such as rapid, one-step process, selective heating to fabricate ZnO thin film under different gases’ environments then utilized it on perovskite solar cells. Structural, optical, and electrical properties of microwave-assisted ZnO thin film are discussed and so are the junction properties of ZnO/Perovskite interface.

Authors : Olof Andersson1, Elin Langhammer1, Patrik Bjöörn1, Jenny Andersson1, Patrik Dahlqvist1, Christoph Langhammer2
Affiliations : 1. Insplorion AB, Medicinaregatan 8A SE-413 90, Gothenburg, Sweden 2. Chalmers University of Technology, Department of Applied Physics, Gothenburg, Sweden

Resume : Nanoplasmonic sensing (NPS) is an optical technology that can be used to detect minute changes in effective refractive index in the vicinity of a sensor substrate. In NPS, the substrate consists of a close-range ordered array of gold nanodisks on a glass support. A thin dielectric film (typically 10 nm Si3N4, SiO2, TiO2, or Al2O3) is used as protective and/or functional layer to protect the gold nanodisks and as substrate material for the sample to be studied. NPS substrates can withstand harsh conditions, thus in situ measurements can be performed e.g. in various solvents and at temperatures up to 600 C in a gas ambient. In Dye Sensitized Solar Cells (DSSCs) the interaction between adsorbed dye molecules and the TiO2 electrode influences the device performance. The kinetics of impregnation of mesoporous TiO2 films with dye molecules is therefore an important step in fabrication of DSSCs. In this contribution we will show how NPS can be used to measure in real time the transport of dye molecules into mesoporous TiO2 photoelectrode films. The results obtained quantify the rate of dye diffusion and show that NPS is a simple and powerful method to follow the impregnation of DSSCs [1]. The glass transition temperature, Tg, of amorphous polymers, such as those used in polymer solar cells, is an important parameter for describing fundamental viscoelastic properties, as well as for targeting technological applications. Confining polymer molecules e.g. at interfaces or in thin films alters the mobility of the molecules and therefore the Tg. Because of the high surface sensitivity of NPS, it is a powerful technology to measure the Tg of thin polymer films [2] and specifically, the variation in phase transition temperatures throughout the depth of polymer films. References [1] V. Gusak, L. Heiniger, V. P. Zhdanov, M. Gratzel, B. Kasemo and C. Langhammer, Energy Environ. Sci., 2013, DOI: 10.1039/C3EE42352B [2] Ferry A. A. Nugroho, Camilla Lindqvist, Amaia Diaz de Zerio Mendaza, Christian Müller, Christoph Langhammer. Submitted

Authors : D. Aureau, M. Bouttemy, J. Vigneron, D. Yamashita, K. Watanabe, J.F. Guillemoles, M. Sugiyama and A. Etcheberry
Affiliations : Lavoisier Institute of Versailles (ILV), UMR 8180 CNRS-UVSQ, IPVF, 45 avenue des Etats Unis, 78035 Versailles, France; NextPV, LIA CNRS-RCAST/U. Tokyo-U. 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan.

Resume : Chemical characterizations of solar materials are a key step to improve the fundamental knowledge of performance of all the cutting edge technologies of solar cells. For the highly efficient III-V multi-junction cells, the capacity to investigate the surface and interface phenomena is crucial to precisely optimize each step of the cells elaboration processes. This is especially true in heterostructures with multiple quantum wells, where the MQW are used to adjust the absorption edge keeping the lattice strain balanced. We have developed a strategy of cross physico-chemical characterization methods combining XPS, nano-Auger and AFM. XPS give chemical information of the different atoms at the surface. Particularly, the fact that Ga or As peaks present wide binding energy difference, and consequently different escape depths, can be used as an inherent probe of chemical modification within the first 10 nm. Furthermore, in-depth analysis can be performed by using Arn+ new generation ionic profiling, with adaptable cluster sizes, enabling to preserve the initial information. Such approach allows to accurately follow the diffusion of particular elements in bulk materials or to access buried interfaces. AFM experiments are combined after all to follow the effect of the various bombardments on the remaining surface morphology. The complementary use of nano-Auger (12nm spot size) enables a complementary local chemical diagnostic either from top Ar+ depth profile or by a direct access from samples sections analyses. Promising results have been obtained in the GaInAsP heterostructures in correlation with PL measurements

Authors : Jeong Kwon a, Jong Hyoek Park b*
Affiliations : aDepartment of Chemical Engineering, Sungkyunkwan University, Suwon 440-746, Republic of Korea bDepartment of Chemical and Biomolecular Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul, Republic of Korea

Resume : As one of the feasible platinum (Pt) alternative counter electrodes (CE) for organic dye-sensitized solar cells (DSSCs) with cobalt (II/III) tris(2,2′-bipyridine) (Co(bpy)32+/3+) redox couple, PEDOT (poly(3,4-ethylenedioxythiophene) having high porous and electrocatalytic active sites was prepared by a simple fabrication process. The resultant PEDOT-CEs exhibited superior electrocatalytic performance than commonly used Pt-CE for Co(bpy)¬32+/3+ reduction reaction (CRR). The optimized PEDOT-CEs showed enhanced electrocatalytic activities and electrochemical stability under repetitive cycling potential, and its charge-transfer resistance (Rct) at the CE/electrolyte interface showed from 0.6 to 1.5 Ω cm2, whose values were much lower than those of the Pt-CE (1.3 to 10.4 Ω cm2) for the CRR. The JK-306-based DSSC with PEDOT-CE exhibited a power conversion efficiency (PCE=10.29%) under one sun illumination (100 mW cm2), whose value is much higher than that of Pt-CE (PCE=9.64%), suggesting that PEDOT-CE can be one of the alternative to Pt-CEs in organic DSSCs with cobalt (II/III) redox couple.

Authors : Mehmet Koç, Mehmet Cem Sahiner, Hisham Nasser, Wiria Soltanpoor, Wisnu Hadibrata, Rasit Turan, Selçuk Yerci
Affiliations : Micro and Nanotechnology Programme, Electrical and Electronics Engineering, The Center for Solar Energy Research and Applications, Middle East Technical University Ankara 06800 Turkey, Electrical and Electronics Engineering Y?ld?r?m Beyaz?t University Ankara 06050 Turkey

Resume : Perovskite as an organic-inorganic material made a strong introduction into the solar industry with its low cost and promising efficiency values respect to commercialized inorganic solar cells. Perovskite has desirable optoelectronic properties for photovoltaic area, with band gap of 1.55eV, high absorption coefficient over a broad range in visible spectrum and high minority carrier lifetime and mobilities. Optical simulations are performed in order to reach higher short circuit currents, n and k values of the perovskite that we fabricated are measured using spectroscopic ellipsometry. In the preliminary results, we found that the structure presented by Tvingstedt et al. can have a Jsc increase upto 1.5 mA/cm2. This study shows that optical coupling of light into the active perovskite layers needs to be taken into account during the design of the solar cells. Also, the results of this study can be applied other thin film solar cells.

Authors : A. Nicolas Filippin,(a) Juan R. Sanchez-Valencia,(a)* Jesús Idígoras,(b) Manuel Macias-Montero,(a) Francisco J. Aparicio,(a) Juan P. Espinos,(a) Fabian Frutos,(c) Angel Barranco,(a) Juan A. Anta (b), Ana Borras(a)*
Affiliations : (a) Nanotechnology on Surfaces Laboratory, ICMS Materials Science Institute of Seville (CSIC-US). C/ Americo Vespucio 49, 41092, Seville (Spain); (b) Departamento de Sistemas Físicos, Químicos y Naturales Universidad Pablo de Olavide, Carretera de Utrera km1, 41013 Seville (Spain); (c) Applied Physic Department, E.T.S. Ingeniería Informática (University of Seville), Avd. Reina Mercedes s/n, 41012 Seville (Spain)

Resume : Development of new fabrication methods for transparent conductive nanoelectrodes compatible with processable substrates and high mass production is very important in fields like nanoelectronics/photonics and solar energy harvesting.(1) Transparent conductive oxides have been traditionally used, being the indium-tin oxide the most popular due to its low resistivity and high transparency. However, the urgency to replace the expensive indium has motivated an intense research to fabricate new nanoelectrodes with high transparency in the UV-VIS-NIR range. Looking to these requirements, the use of tailored porous conductive nanostructures appears as a promising route.(2) We report the fabrication of platinum nanoelectrodes in the form of percolated layers and supported nanocolumns by vacuum/plasma processing of the Pt octaethylporphyrin(PtOEP) precursor. The protocol combines remote plasma assisted deposition at RT and soft plasma etching treatments below 180ºC being compatible with many processable substrates. Transparency in the UV-Vis-NIR range can be adjusted between 70 and 1% with a sheet resistivity of 1350 and 120 Ω/□, respectively. The catalytic properties of the nanoelectrodes are further demonstrated by their implementation as counter electrode in a dye sensitized solar cell (DSC) surpassing the performance of commercial Pt counterelectrodes in a 20% of the overall cell efficiency. (1) Hu, L. et al. MRS Bull. 2011, 36, 760–765 (2) Layani, M. et al. S. Nanoscale 2014, 6, 5581

Authors : Emre Coskun3, Tahir Colakoglu2, Hasan Huseyin Gullu1-2, Ozge Bayraklı1-2, Mehmet Parlak1-2
Affiliations : 1. Department of Physics, Middle East Technical University (METU), Ankara 06800, Turkey 2. Center for Solar Energy Research and Applications (GÜNAM), METU, Ankara 06800, Turkey 3. Department of Physics, Canakkale Onsekiz Mart University, Canakkale 17100, Turkey

Resume : In this work, electrical properties of n-In2Se3/p-Si nanowire heterojunction diodes were investigated depending on the nanowire lengths and also as a comparative study of n-In2Se3/p-Si planar reference device. Metal-assisted etching method performed by AgNO3 and HF solution at different etching times was applied to fabricate vertically oriented Si nanowires on p-type (111) mono-crystalline 600 μm Si wafers with the resistivity value of 1 - 3 (Ω.cm). In this etching process, the lengths of the p-type Si nanowires were controlled by the etching time, and so that three different Si wafer substrates were prepared with about 1.75, 3.0 and 6.0 nm nanowire lengths. The heterojunction diodes were constructed by depositing 200 nm n-In2Se3 thin film layer using physical vapor deposition technique onto these fabricated Si nanowires and planar substrates. Thin film deposition was also carried out on commercial soda lime glass substrates at the same condition. Initially, the structural, optical and electrical properties of the In2Se3 thin film deposited on the glass substrates were analyzed. Then, detailed electrical characterization of these heterojunction diodes were performed by the help of current-voltage (I-V) measurements to understand their electrical properties depending on length of the nanowire on Si substrate. The fabricated diodes exhibited rectifying characteristics and from these I-V measurements, the advantages of the nanowire geometry compared to reference device were discussed based on the calculated device parameters.

Authors : Nima Sohrabnia, Şevki Can Cevher,Gönül Hızalan,Levent Toppare*†and Ali Çirpan*† ‡
Affiliations : *Department of Chemistry Middle East Technical University,Ankara †Department of Polymer Science and technology polymer science and technology ‡ Department of Micro & NanotechnologyMiddle East Technical University,Ankara

Resume : In recent decades generation of electricity become main concern in the world. As traditional fuels became depleted, humanity tries to find promising solution for production of energy and design devices with high efficiencies. Thereby conjugated polymers became promising candidates for organic optoelectronic applications such as organic Photovoltaics (OPVs), Organic Light Emitting Diodes (OLEDs) and Electrochromic Devices (ECs) because of their low cost of production. Here in, we were synthesized Phenanthrenyl-Imidazole based polymers for Polymer Light Emitting Diodes (PLED) applications. The planarity of these fused cyclic monomer is expected to form regioregular copolymers that had lower band gap and enhanced electron transferring abilities.2-(2,5-dibromothiophen-3-yl)-1-(4-hexylphenyl)-1H-phenanthro[9,10-d]imidazole (M1) polymerized with 9,9-Dioctylfluorene-2,7-diboronic acid bis(1,3-propanediol)ester via Stille coupling to obtain P1. After that device structure was optimized as glass substrate/ITO/P1/Ca/AL structure and characterized by Current Density-Voltage. This polymer shows luminous efficiency of 0.42 cdA-1 at a brightness of 900 cdm-2 with turn on voltage of 12.5. The Commission Internationale d’Eclairage coordinates of this polymer assigned as (0.37, 0.42). The absorption properties of P1 in solution and film were investigated via UV and Photoluminescence Spectroscopes. Molecular weight and molecular structure of polymer characterized with GPC and NMR analysis.

Authors : Daragh Mullarkey*1, Elisabetta Arca1, Linda Cattin2, Jean Christian Bernède3, Igor Shvets1
Affiliations : 1: School of Physics and CRANN, Trinity College Dublin, University of Dublin, Ireland 2: Universitè de Nantes, Institut des Matériaux Jean Rouxel, France 3: Universitè de Nantes, MOLTECH-Anjou, France

Resume : The use of undoped Cr2O3 and p-type Cr2O3:Mg as an anode buffer layer in organic solar cells is explored. The effects of buffer layer thickness, growth conditions and roughness on the properties of the solar cell were studied. These effects were investigated for solar cells grown on both indium tin oxide and fluorine doped tin oxide. In both cases, Cr2O3 and Cr2O3:Mg were found to increase the efficiency of the solar cell. Furthermore, the band offset between the various anodes and anode buffer layers was studied by X-ray Photoelectron Spectroscopy (XPS) and Ultra Violet Photoelectron Spectroscopy (UPS). This band offset is discussed in terms of the efficiency of the solar cell.

Authors : Aashir Waleed*, Mohammad Mahdi Tavakoli*, Zhiyong Fan*
Affiliations : *Department of Electronic and Computer Engineering, The Hong Kong University of Science and Technology, Hong Kong,China

Resume : In the past, extensive research on CdTe solar cell devices have been done to explore Ohmic back contact of CdTe layer in conventional superstrate device structure (glass/TCO (transparent conducting oxide layer)/CdS/ CdTe/ back contact) to improve the device performance. However, no considerable attention has been paid to overcome the device shunting issue caused by pinholes and non-uniformity of thin CdS layer, which causes significant reduction in device performance and yield. To increase the transparency of CdS film this layer is normally less than 100 nm in thickness in CdTe solar cell device. To overcome non-uniformity and pin holes of thin CdS layer issue, there could be two solutions of this problem, either use highly resistive transparent conducting oxide layer with low resistance TCO (e.g., Tin Oxide or Zinc Oxide with Fluorine-doped tin oxide) or by using a thick CdS layer. But increasing the thickness can cause high light absorption losses and parasitic light absorption in CdS. Absorption losses in CdS layer can cause significant reduction of fill factor and device performance. In this work, we have addressed conformal layer issue of CdS by inserting a compact sputtered Titanium dioxide (TiO2) buffer layer between Fluorine-doped tin oxide and CdS. Zinc oxide could also be used in place of TiO2 but ZnO has low power conversion efficiency and low stability in humid environments. A study for thickness effect of TiO2 layer on device yield (working devices per sample) and open air stability was carried by adding different thickness ranging from 0 to 100 nm. It was found that TiO2 layer with 20 nm-thick performed better than other thick layers of TiO2, device yield and open air sustainability were improved significantly. Device yield of 80% and device efficiency of more than 8% were recorded for 20 nm TiO2, which were 20% and 6% without TiO2 layer, respectively. A comparative study for air sustainability showed device with TiO2 had enhanced open air stability over recorded time span of 60 days. In this work low cost and simple fabrication methods i.e., electrochemical deposition and chemical bath deposition were used for CdS and CdTe layers, respectively, they are cost effective approaches for flexible photovoltaic device fabrication. Overall, here we discovered that device performance is dependent on not only ohmic back contact but also uniformity of cadmium sulphide window layer over TCO and inclusion of TiO2 buffer layer can help to improve device performance and stability.

Start atSubject View AllNum.Add
Advanced Characterization I : Bernd Stannowski
Authors : Iver Lauermann, Roland Mainz, Wolfram Calvet, Bünyamin Ümsür, Tatiana Olar, Alexander Steigert, Martha Ch. Lux-Steiner
Affiliations : Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109 Berlin, Germany

Resume : Spectroscopic methods based on synchrotron radiation in the energy range of soft to tender x-rays yield valuable information on chemical, structural and electronic surface, interface and bulk properties of thin film solar cells and their components. This knowledge is necessary to understand and improve these photovoltaic devices, which consist of stacks of several different materials, in a systematic way. In this presentation we show some synchrotron based state-of-the-art methods for the analysis of polycrystalline thin film materials and entire photovoltaic devices and their limitations. Using results obtained with different end stations (CISSY, HIKE, Suricat, In-situ PVD) at the BESSY II synchrotron in Berlin, Germany, we show how synchrotron excited photoelectron spectroscopy (PES), x-ray absorption spectroscopy (XAS), x-ray diffraction (XRD) and soft X-ray emission spectroscopy (XES) have increased our knowledge of the properties of bulk phases, surfaces and “hidden” interfaces of these systems. Examples of recent results are the determination of composition-dependent conduction band shifts of absorber materials by XAS, depth-dependent composition analysis by high kinetic energy PES and identification of different phases by in-situ XRD measurements during the formation of compound semiconductor absorber layers from precursor stacks.

Authors : M. Sowińska1,*, C. Das1, K.Henkel1, K. Wojciechowski2, H. Snaith2 and D. Schmeißer1
Affiliations : 11Brandenburgische Technische Universität Cottbus–Senftenberg, Angewandte Physik-Sensorik, Konrad-Wachsmann-Allee 17, 03046 Cottbus, Germany 2Clarendon Laboratory, University of Oxford, Parks Road, Oxford, OX13PU, UK *Corresponding author e-mail address:

Resume : Organic-inorganic perovskites like CH3NH3PbI3 films represent a new paradigm for photovoltaics, which have the potential to overcome the performance limits of current technologies and achieve low cost and high versatility. Although the power conversion efficiency of the CH3NH3PbI3-based perovskite solar cells exceeded already 20%, a number of key issues must be solved before the wide-spread commercialization will be possible. A study of vacancy-mediated migration of I-, Pb2+ and CH3NH3- ions and their relative activation energies suggests, that the migration of halide vacancies to and from the interfaces in the solar cell during its operation is the main conduction mechanism [1,2]. In this work, we are presenting laboratory- and high resolution synchrotron-based spectroscopic studies of the CH3NH3PbI3 perovskite films. For example, the resonant X-ray photoelectron (resPES) study at the N1s absorption edge indicates that the contribution of nitrogen into the conduction mechanism of the CH3NH3PbI3 perovskite films should not be neglected. Moreover, different core level binding energies are observed in the X-ray photoelectron spectra (XPS) of the perovskite when different excitation energies are used. This result indicates that different potentials are at the surface and in the CH3NH3PbI3 film bulk. Detailed XPS and resPES data analysis will be presented. [1] Y. Zhang et al., Mater. Horiz. 2, (2015) 315. [2] J.M Azpiroz et al., Energy Environ. Sci. 8, (2015) 2118.

Authors : Manoj Jaysankar, Weiming Qiu, Maarten Debucquoy, David Cheyns, Ulrich W. Paetzold, Jef Poortmans
Affiliations : KU Leuven (Belgium), IMEC (Belgium); KU Leuven (Belgium), IMEC (Belgium); IMEC (Belgium); IMEC (Belgium); IMEC (Belgium); KU Leuven (Belgium), IMEC (Belgium)

Resume : In recent years, organic-inorganic metal halide perovskite materials have evolved as highly efficient photovoltaic competitors to Silicon. Another option is to utilize the variety of bandgaps found in this class of materials and combine wide-bandgap thin-film photovoltaic perovskites in tandem with silicon solar cells. With careful opto-electronic engineering, these tandem solar cells can yield power conversion efficiencies beyond 30%. Here, we present a systematic material study on CH3NH3Pb(I0.6Br0.4)3 which has an optimal band gap of 1.77 eV. Crystallization dynamics in spin-coated CH3NH3Pb(I0.6Br0.4)3 films were studied by varying the annealing conditions of the films. The impact of annealing temperature and duration on crystallinity, carrier lifetime and average grain size of the active layers was studied using X-ray diffraction, time-resolved photoluminescence and scanning electron microscopy. The solar cells fabricated with these films show a clear correlation between crystallization dynamics in the perovskite films and device performance. Analysis of grain growth kinetics with extraction of activation energy for grain boundary mobility, and grain growth exponent for the perovskite layers annealed at different temperatures provide a quantitative analysis of quality of the layers. These insights linking the fundamental material characteristics of the perovskite films with device performance are crucial for further development of high-performance perovskite photovoltaics.

Authors : Roland Mainz, Helena Stange, Humberto Rodriguez-Alvarez, Marc-Daniel Heinemann, Thomas Unold
Affiliations : Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109 Berlin, Germany; Technische Universität Berlin, Institut für Werkstoffwissenschaften, Ernst-Reuter-Platz 1, 10587 Berlin, Germany

Resume : The physical properties of semiconducting thin films are influenced by the course of their growth process. Hence, a detailed understanding of the mechanisms taking place during film growth is important for a targeted development and optimization of thin film solar cell fabrication processes. This is particularly true for complex compound systems such as Cu(In,Ga)Se2 or Cu2ZnSn(S,Se)4, where the process parameter space is huge. Microstructural properties such as compositional gradients, grain size and extended defects may crucially influence the resulting performance of the solar cell. In-situ methods such as x-ray diffraction, x-ray fluorescence analysis, or white light reflectometry are able to provide time-resolved information on the evolution of these properties, potentially pointing to new process pathways or revealing which process steps are decisive for reaching high film quality. However, due to the complexity of the reactions and the interplay of different mechanisms, it is often not possible to directly extract all information contained in the data. In this contribution, we show that a more complete picture and understanding of the formation of compositional gradients, stress-relaxation, and grain growth in Cu(In,Ga)Se2 or Cu2ZnSn(S,Se)4 can be gained when the experimental real-time data are complemented by numerical modelling.

Silicon I : Iver Lauermann
Authors : B. Stannowski1, L. Korte2, L. Mazzarella1, D. Meza2, A. B. Morales-Vilches1, M. Hendrichs1, S. Calnan1, S. Kirner1, T. Frijnts1, M. Mews2, H. Scherg-Kurmes3, R. Muydinov3, B. Szyszka3, B. Rech2, R. Schlatmann1
Affiliations : 1 Helmholtz-Zentrum Berlin, PVcomB, Schwarzschildstraße 3, 12489 Berlin, Germany 2 Helmholtz-Zentrum Berlin, Institute Silicon Photovoltaics, Kekuléstr. 5, 12489 Berlin, Germany 3 Technische Universität Berlin, Einsteinufer 25, 10587 Berlin, Germany

Resume : Solar cells with diffused homo-emitter on p type crystalline silicon (c-Si) are a mature technology in mass production. As an alternative, a-Si/c-Si heterojunction (SHJ) cells based on n-type Si wafers are considered a technology with higher efficiency potential and better energy yield. Moreover, a lean cell production process at temperatures <200°C is compatible with very thin wafers. Here, the challenge lies in finding industry compatible processes and materials to allow low-cost production of high efficiency cells. Highly transparent front-side electrodes and ultra-low contact resistance materials are required. In our contribution we discuss: (1) standard indium-oxide as well as zinc oxide as a low-cost alternative electrode material, and their contribution to minimize optical and resistive losses [1, 2]; (2) Combinations of doped nano-crystalline silicon and silicon oxides, which have been developed as contact layers to minimize both the parasitic absorption and the contact resistance [3, 4]; (3) High work-function metal oxide layers (e.g. MoOx, WOx), which have recently been suggested as possible candidates to replace the doped silicon [5]. References [1] T. Koida et al., Solar Energy Materials & Solar Cells 93 (2009) 851–854 [2] H. Scherg-Kurmes et al., Thin Solid Films 594 (2015) 316–322 [3] L. Mazzarella et al., Appl. Phys. Lett. 106 (2015) 023902 [4] L. Mazzarella et al., Energy Procedia 77 (2015) 304 – 310 [5] C. Battaglia et al., Appl. Phys. Lett. 104 (2014) 113902

Authors : V. Smirnov 1, F. Urbain 1, J.- P. Becker 1, K. Welter 1, W. Jaegermann 2, F. Finger 1
Affiliations : 1 Forschungszentrum Jülich GmbH, IEK-5 Photovoltaik, Jülich, Germany 2 TU Darmstadt, Darmstadt, Germany

Resume : We report on the application of multijunction solar cells in photoelectrochemical devices for hydrogen production. A chemical reaction to generate hydrogen through photoelectrolysis of water requires photovoltages over 1.5 V to run autonomously. The solar-to-hydrogen (STH) efficiency is determined by the photocurrent at the respective required voltage. We have shown successful application of multijunction solar cells in PEC systems with 9.5% STH efficiency [1]. Here we investigate photoelectrochemical system in more details, where the multijunction solar cells made of amorphous (a-Si:H) and microcrystalline (μc-Si:H) silicon cover up a wide photovoltage range in combination with high photocurrents. We study a-Si:H/µc-Si:H and a-Si:H/a-Si:H tandem junction, a-Si:H/µc-Si:H/µc-Si:H and a-Si:H/a-Si:H/µc-Si:H triple junction, and a-Si:H/a-Si:H/µc-Si:H/µc-Si:H quadruple junction solar cells, which provide open-circuit voltages Voc ranging from 1.5 to 2.8 V, along with initial efficiencies up to 13.6 %. The influence of varied illumination intensities on the performance of both multijunction solar cells and PEC devices is addressed. The trade-offs between Voc, short circuit current density and photoelectrochemical performance are studied over a wide range of parameters (such as photovoltages-photocurrents, various catalysts and overpotential losses) in an integrated photoelectrochemical device configuration. 1. F. Urbain, V. Smirnov et al, Energy Environ. Sci. 9, 145 (2016).

Authors : Tim Frijnts (1), Natalie Preissler (1), Bernd Rech (2), Rutger Schlatmann (1)
Affiliations : 1.PVcomB, Helmholtz Zentrum Berlin für Materialen und Energie GmbH, Schwarzschildstraße 3, 12489 Berlin, Germany ; 2.Institute for Silicon Photovoltaics, Helmholtz Zentrum Berlin für Materialen und Energie GmbH, Kekuléstraße 5, 12489 Berlin, Germany

Resume : Backside-contact solar cells were fabricated on 10 µm thick, boron doped, liquid phase crystallized silicon (LPC-Si) on glass substrates, with interlayers between the glass and the silicon based on either silicon oxynitride (SiON) or aluminium oxide (Al2O3). The SiON layer contains positive fixed charges, which results in a charge inversion layer on the silicon side of the Si-SiON interface. On the other hand, the Al2O3 layer contains negative fixed charges which results in a charge accumulation layer at the interface. In this contribution we show our results on the fixed charge density in the SiON and Al2O3 layer determined with C-V measurements. By employing large area external quantum efficiency measurements we show that, for the cells with SiON based layers, minority charge carriers are collected from outside the cell area through the inversion layer. Light beam induced current measurements reveal that the loss due to incomplete collection below the absorber contact (electrical shading) is reduced from 10.5% for the Al2O3 samples to 7% for the SiON samples, presumably due to the collection of charge carriers through the inversion layer. This effect can also explain the previously observed large electrical shading loss of 11% for n-doped compared to p-doped LPC-Si solar cells on SiON based interlayers. Finally, our results point out a way to collect charge carriers below the absorber contact of backside-contact solar cells despite a relatively small diffusion length.

Authors : M. Al-Amin, J.D. Murphy
Affiliations : School of Engineering, University of Warwick, UK

Resume : Minority carrier lifetime is the key materials parameter for multicrystalline silicon (mc-Si) substrates for solar cells. Lifetime in mc-Si is limited by recombination associated with metallic impurities in many forms, including point-like defects, precipitates and impurities bound to or precipitated at structural defects such as dislocations or grain boundaries. Some metallic impurities, such as interstitial iron, are sufficiently mobile that they can be redistributed by annealing at low temperatures (< 500 °C) and such internal gettering processes can be used to enhance lifetime. We have conducted a detailed study into the effects of long low temperature annealing on the lifetime and interstitial iron distribution in mc-Si from different regions of a directionally-solidified block. Systematic sets of experiments are conducted at different stages in the cell process (as-received and after phosphorus diffusion gettering). Photoluminescence imaging is used to monitor the evolution of lifetime and interstitial iron concentration with processing time. The results are strongly dependent on the choice of surface passivation, with possible hydrogenation from silicon nitride films having a strong effect. We find long low temperature annealing can result in substantial improvements in carrier lifetime with and without possible hydrogenation. The impact is greatest in red zone material from the bottom of the block, in which lifetime improvements of a factor of ~7 have been achieved.

Authors : A. Ulyashin*, A. Ciftja**, G. Stokkan**, A. Azar*, P.A. Carvalho*, S. Wilson**, W. Dall**, J.M. Pó***, J. Maia Alves***, J.M. Serra***
Affiliations : *SINTEF, Oslo, Norway **SINTEF, Trondheim, Norway ***Instituto Dom Luiz, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal

Resume : It is demonstrated that polycrystalline free standing Si powder based wafers can be processed using hot pressing of ingots at temperatures around 1300 oC followed by the wire saw based wafering of such ingots. Properties of Si powder based wafers have been studied by electrical, SEM, EDS, Raman and EBSD analysis. It has been demonstrated that resistivity of Si powder based substrates can be varied by "in-situ" doping before the sintering process, by mixing Si and Boron powders together. Possible application of Si powder sintered substrates for PV is discussed. Moreover, it has been demonstrated that using an optical furnace that consists of an array of laser diode bars, it is possible to produce a floating molten zone and to realize full crystallization of Si powder sintered samples. As a result, large grain poly-Si substrates can be fabricated, which were analyzed by SEM and EBSD. It is concluded that combination of sintering and laser recrystallization steps being applied to Si powder based wafers, can be considered as a low-cost alternative for Si based wafers and layers for photovoltaic applications. The work described in the paper is finished so the past tense is most appropriate. Further, definite language should be used wherever possible, see below: In this work, polycrystalline free standing Si powder based wafers were produced using hot pressing of ingots at temperatures around 1300 oC, followed by wire saw wafering. The properties of the Si powder based wafers were studied by electrical, SEM, EDS, Raman and EBSD analyses. The resistivity of Si powder based substrates was varied by "in-situ" doping before the sintering process, by mixing Si and Boron powders together. Possible application of sintered Si powder substrates for PV was discussed. An optical furnace consisting of an array of laser diodes was used to produce a floating molten zone and to realize full crystallization of sintered Si powder samples. Large grain poly-Si substrates were produced, which were analyzed by SEM and EBSD. It was concluded that the application of sintering and laser recrystallization steps to Si powder based wafers could be considered as a low-cost alternative for Si based wafers and layers for photovoltaic applications.

Authors : P. Pikna 1, V. Skoromets 2, C. Becker 3, A. Fejfar 1, P. Kužel 2
Affiliations : 1 Institute of Physics ASCR, Cukrovarnická 10, 16253 Prague 6, Czech Republic 2 Institute of Physics ASCR, Na Slovance 2, 18221 Prague 8, Czech Republic 3 Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Kekuléstraße 5, 12489 Berlin, Germany

Resume : Thin film polycrystalline silicon solar cells combine the advantages of both thin film technologies, i.e. low material and energy consumption for manufacturing and high crystalline quality of wafer-based solar cells. Crystalline quality of silicon thin films can be characterized by both open-circuit voltage of the solar cell and according to our experiments also by transient terahertz spectroscopy [1]. Optical pump terahertz probe spectroscopy enables a contactless photoconductivity inspection of solar cells giving a detailed insight into recombination processes that take place at defects, i.e. interfaces, grain boundaries, dislocations. A series of polycrystalline Si thin film solar cells with different silicon quality was prepared by their treatment in hydrogen plasma under various technological conditions. A clear correlation was found between the carrier trapping rate in the absorber layer of the cells and their open-circuit voltage. In this contribution we will develop this new approach to analyse also alternative passivation approaches, e.g. using the water vapour passivation [2]. The origins of the correlation of the trapping rates probed on picosecond scale and quasi steady state open circuit voltage will be discussed. [1] P. Pikna, V. Skoromets, C. Becker, A. Fejfar, P. Kužel, Thin film polycrystalline Si solar cells studied in transient regime by optical pump–terahertz probe spectroscopy, Applied Physics Letters. 107 (2015) 233901. doi:10.1063/1.4937388. [2] P. Pikna, M. Müller, A. Fejfar, Passivation effect of water vapour on thin film polycrystalline silicon solar cells, 26th International Conference on Amorphous and Nanocrystalline Semiconductors, Aachen, Germany, 2015. This research was supported by Czech Science Foundation project 13-12386S.

Authors : Liana N. Inasaridze (a), Iliya V. Martynov (a), Baili Li (b), Diana K. Susarova (a), Alexander V. Mumyatov (a), Alexander I. Shames (b), Eugene A. Katz (b), and Pavel A. Troshin (a,c)
Affiliations : (a) Institute for Problems of Chemical Physics of RAS, Semenov ave. 1, Chernogolovka, Moscow region, 142432, Russia. E-mail: (b) Ben-Gurion University of the Negev, Beer Sheva, Israel (c) Skolkovo Institute of Science and Technology, Moscow, Russian Federation;

Resume : Organic solar cells have demonstrated efficiencies above 10% recently, though their practical implementation is restricted mainly due to insufficient operational stability. In particular, fullerenes were shown to undergo facile photodimerization, which is currently considered as the main source of burn-in degradation effects in organic solar cells [A. Distler et al., 2014, 4, 1300693; T. Heumueller et al., Energy Environ. Sci., 2016, 9, 247]. In this talk, we will present results of our systematic study of ~20 fullerene derivatives bearing different organic addends attached to the carbon cage. The main factors influencing the photodimerization of different materials including standard [60]PCBM will be discussed. Some details of the mechanism of the photoinduced cross-linking reaction will be unraveled and few types of the photochemically stable fullerene derivatives will be presented. In the second part of the talk, we will focus on the alternative photodegradation pathway of fullerene derivatives leading to the generation and accumulation of stable radical species. These paramagnetic centers behave as traps for mobile charge carriers and affect severely the performance of organic solar cells. Finally, we will compare the impacts of the radical and non-radical (dimerization) photodegradation pathways of fullerenes and their derivatives and outline future research directions for designing fairly stable n-type materials for efficient and durable organic photovoltaics.

Authors : Cornlia Rodenburg, Robert Masters*, J. Sharp*, Ian M. Ross˟, Andrew Pearson', Tom Glen', Athene M Donald'. A, Howie', Maurizio Dapor°, Yiwei Zhang˜, and David G Lidzey˜
Affiliations : *Department of Materials Science and Engineering, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield, S1 3JD, UK; ˟Department of Electronic & Electrical Engineering,, University of Sheffield, Mappin Street, Sheffield, S1 3JD, UK; 'Department of Physics, University of Cambridge, Cavendish Laboratory, 19 J J Thomson Avenue, Cambridge, CB3 0HE, UK; °European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT), Fondazione Bruno Kessler (FBK),Via Sommarive, 18 - I-38123 Povo (TN), Italy; ˜ Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH, UK

Resume : It is now well established that the degree of crystallinity affects the lifetime of polymer based organic solar cells and air exposure is mainly thought to be responsible for the degradation. Here we show that in the absence of air (or light) but in the presence of electron irradiation similar effects to that known as burn-in in solar P3HT:PCBM based solar cells can be observed for P3HT with relatively low crystalline order. Highly ordered P3HT, and a novel high efficiency polymer (PffBT4T) do not show such charge induced “burn-in effect”. The above observation is based on the changes in the low loss (plasmon) region of electron energy loss spectra induced by prolonged electron-beam exposure. Detailed analysis of this region suggests slight changes in the band-gap of the P3HT, depending on P3HT morphology. We further establish through secondary electron spectroscopy in a low-voltage SEM that this change in band gap has a profound influence on charge transport which is reflected in substantial differences in the emission of low energy secondary electrons. We also demonstrate that the distinctive differences in secondary electron spectra shape can be exploited to map the local crystallinity distribution in P3HT, by using energy filter low voltage scanning electron microscopy, thus providing a new tool that can aid efficient morphology engineering. Our findings are in agreement with many reports that advocate a higher degree of crystallinity in order to increase device lifetimes but our observation also implies that preventing charge built -up in the active layer through appropriate device design & morphology engineering needs to be considered as a life extending measure in addition to reducing air exposure.

Authors : K.J. Lee,a C. T. Howells,b K. Marbou,b H. Kim,c J.H. Kim,de S.J. Kim,f S.Y. Kim,fg C. Adachi,d J.W. Wu,a J.-C. Ribierre,d D.W. Kim,a P. Andréa,f*
Affiliations : a Ewha Womans University (Seoul, Korea) ; b Masdar Institute of Science and Technology (Abu Dhabi, UAE) ; c Clean Energy Research Center, Korea Institute of Science and Technology (Seoul, South Korea) ; d Kyushu University (Fukuoka, Japan) ; e Pukyong National University (Busan, South Korea) ; f Ellipso Technology Co. Ltd. (Suwon, South Korea) ; g Ajou University (Suwon, South Korea) ; f RIKEN (Wakoshi, Japan)

Resume : Organic and hybrid organic-inorganic optoelectronics are the subject of intensive research efforts partially motivated by their potentials to achieve low processing cost devices, for instance via roll-to-roll and inkjet printing processes, as well as their promises to deliver exciting mechanical properties.[1] In the present work,[2] the hole-transport layer of two organic solar cells was doped and shown to strongly influence the device efficiency. A combination of near-field microscopy, Kelvin probes, UV photoemission spectroscopy, conductivity, steady state and time resolved optical spectroscopy, as well as ellipsometry were combined with electro-optical modelling to gain insight into the mechanism involved in photovoltaic structures. We show how a simple PEDOT:PSS doping can alter simultaneously interfacial work-functions, built-in potentials and optical constants to impact on organic solar cell efficiency.

Authors : Irina V. Klimovich (a), Diana K.Susarova (a), Olga M. Muhacheva (a), Fedor A. Prudnov (a), Liana N. Inasaridze (a), Lukash M. Przypis (c) and Pavel A. Troshin (a,b)
Affiliations : (a) Institute for Problems of Chemical Physics of the Russian Academy of Sciences (IPCP RAS), Chernogolovka, Russian Federation; (b) Skolkovo Institute of Science and Technology, Moscow, Russian Federation; (c) Silesian Technical University, Gliwice, Poland

Resume : Great improvement in the performance of organic bulk-heterojunction solar cells was achieved mostly due to successful design of novel photoactive materials. Recently, we have developed promising electron-donor copolymers (X-TTBTBTT-)n (X – fluorine, carbazole; B –benzothiadiazole; T – thiophene), which demonstrate good performances both in spin-coated (up to 7%) [1-3] and roll-to-roll processed (up to 6.2%) [4] devices. In the present work we were aiming to improve further the optoelectronic characteristics of the designed copolymers (X-TTATATT-)n via a systematic variation of the acceptor (A) units. We synthesized and investigated materials based on 2-alkylbenzotriazole, several different quinoxaline derivatives, benzoxadiazole and 5,6-bis(octyloxy)benzoxadiazole. We will discuss how the chemical structure of the acceptor building blocks affects the optoelectronic and physicochemical properties of the materials as well as their performance in organic solar cells. The revealed correlations provide useful guidelines for designing novel copolymers based on extended TTATATT units for efficient organic photovoltaics. [1] A. V. Akkuratov et al., Macromolecules, 2015, 48, pp 2013–2021 [2] I. E. Kuznetsov et al., Chem. Commun., 2015, 51, 7562-7564 [3] A. V. Akkuratov et al., J. Mater. Chem. A, 2016, submitted [4] I. Burgués-Ceballos et al., ChemSusChem, 2015, 8, 4209

Authors : Oskar J. Sandberg, Mathias Nyman, Staffan Dahlström, and Ronald Österbacka
Affiliations : Physics, Faculty of Science and Technology and Center for Functional Materials, Åbo Akademi University, Turku, Finland

Resume : A method to directly determine doping profiles in sandwich-type thin-film devices of low mobility materials is presented. The method is an extension of the Charge Extraction by a Linearly Increasing Voltage (CELIV) technique which is one of the most common methods to measure the charge transport properties in (undoped) low mobility materials. We recently showed that when the doping concentration in the active layer is high enough, so that the depletion region is smaller than the device thickness, the charge extraction transients become purely capacitive when a slowly enough linearly increasing voltage pulse is applied [1]. In this doping-induced capacitive regime of CELIV (doping-CELIV) the doping concentration and built-in potential of the device can be obtained, assuming a constant doping profile. This method has thus far been successfully applied to polymer:fullerene, organic small molecule, and CZTSSe-based solar cells. In this work, we have extended the method of using the capacitive regime of CELIV to an arbitrary doping profile. The method is demonstrated both with computer simulations based on a drift-diffusion approach and experimentally on organic thin-film diodes. Furthermore, using a similar approach, but on undoped devices with one ohmic contact, we show that the density of injected charge due to Fermi level alignment at the ohmic contact can be determined as well. [1] Oskar J. Sandberg, Mathias Nyman, and Ronald Österbacka, Organic Electronics 15 3413–3420 (2014)

Start atSubject View AllNum.Add
Authors : M. J. Mendes (1), O. Sanchez (1), A. Araújo (1), S. Morawiec (2), A. Vicente (1), A. Lyubchyk (1), T. Mateus (1), H. Águas (1), I. Ferreira (1), I. Crupi (3), F. Priolo (2,3), E. Fortunato (1) and R. Martins (1)
Affiliations : (1) i3N/CENIMAT, Department of Materials Science, Faculty of Science and Technology, Universidade NOVA de Lisboa and CEMOP/UNINOVA, Campus de Caparica, 2829-516 Caparica, Portugal; (2) Dipartimento di Fisica e Astronomia, Università di Catania, via S. Sofia 64, 95123 Catania, Italy (3) MATIS CNR-IMM, via S. Sofia 64, 95123 Catania, Italy

Resume : Light management is the most promising route to develop thin film PV. Recently, several strategies were proposed employing the scattering and/or anti-reflection properties of nanophotonic elements, with dimensions comparable or below the illuminating wavelengths, to trap light in solar cells. For the cells’ rear, resonant plasmonic nanoparticles (NPs) can enhance the path length of the near-infrared light reaching the cells’ back contact. High-performing plasmonic back reflector (PBR) structures, produced by an innovative wet-coating method [1], were incorporated in thin film Si cells. The strong scattering properties of the optimally-sized colloidal NPs allow remarkable enhancements, of 43% and 41%, respectively in the cells’ current and efficiency [2]. For the cells’ front, high-index wavelength-sized dielectric features are shown to produce pronounced anti-reflection and forward-scattering, in the regime of wave-optics. Optimized TiO2 half-spheroids scatter as strongly as plasmonic NPs but without the associated parasitic absorption [3], generating superior absorption in the cells, mainly in the UV-visible range, and current and efficiency enhancements up to 50%. Therefore, broadband light trapping close to the theoretical limits can be expected for thin film cells with a combination of plasmonic (at the rear) and high-index dielectric (at the front) photonic structures. [1] M.J. Mendes et al. Nanoscale (2014) [2] M.J. Mendes et al. Nanotechnology (2015) [3] M.J. Mendes et al. Optics Express (2011)

Authors : Lefteris Danos, Nicholas Alderman, Liping Fang, Martin C. Grossel and Tomas Markvart
Affiliations : Lefteris Danos: Department of Chemistry, Energy Lancaster, Lancaster University, Lancaster, LA1 4YB Nicholas Alderman, Liping Fang and Tomas Markvart: Solar Energy Laboratory, Engineering and the Environment, University of Southampton, Southampton, SO17 1BJ Martin C. Grossel: Department of Chemistry University of Southampton, Southampton, SO17 1BJ

Resume : Silicon photosensitisation using light harvesting structures represents an attractive solution for reducing the amount of semiconductor material needed by up to two orders of magnitude in the manufacture of solar cells [1-3]. Furthermore separating the photovoltaic process into two separate steps, an absorption step and a charge separation step, can provide a solution for low cost solar electricity. The direct attachment of alkyl layers [4-6] and chromophores [7-9] represents an attractive solution to combine the excellent optical properties of dye molecules with the electronic properties of thin silicon converters. The above approach divides the photovoltaic conversion process into two processes consisting of an energy collector (light harvesting) which absorbs light with a high optical absorption cross-section, and transfers energy to a semiconductor converter (silicon) which efficiently separates the photo-generated charges and produces electricity. The resulting organic-inorganic structure presents a step change in thinking in photovoltaic energy conversion. A chlorination–alkylation procedure has been investigated with a view to improving the surface passivation properties on silicon [4-6]. We have found that increasing surface coverage of the alkyl monolayer raises the measured Surface Photovoltage (SPV) and increases the electron-hole recombination lifetime. We investigate the potential of photosensitization of silicon surfaces using covalently attached protoporphyrin IX derivative molecules. The illuminated surface results in the Interaction between the near field of the molecular dipole and the transition dipole moment of the electron transition between the valence and conduction band of the semiconductor. Experimental verification of the near field interaction of dyes on surfaces has been carried out in the past by monitoring the fluorescence lifetime quenching near the surface. We present time resolved fluorescence quenching measurements for dyes directly attached on the silicon surface. In particular, we investigate the near field interaction of the excited dye at distances to the silicon surface less than 2nm. References 1. N. Alderman, L. Danos, L. Fang, T. Parel, and T. Markvart, in Photovoltaic Specialist Conference (PVSC), 2014 IEEE 40th, 2014, pp. 17–21. 2. T. Markvart, L. Danos, N. Alderman, L. Fang, and T. Parel, in 27th European Photovoltaic Solar Energy Conference, Frankfurt, 2012, pp. 1–6. 3. T. Markvart, L. Danos, L. Fang, T. Parel, and N. Soleimani, RSC Adv., 2012, 2, 3173. 4. N. Alderman, M. Adib Ibrahim, L. Danos, M. C. Grossel, and T. Markvart, Appl. Phys. Lett., 2013, 103, 081603. 5. N. Alderman, L. Danos, M. C. Grossel, and T. Markvart, RSC Adv., 2013, 3, 20125. 6. N. Alderman, L. Danos, C. Grossel, and T. Markvart, RSC Adv., 2012, 2, 7669–7672. 7. L. Fang, K. S. Kiang, N. P. Alderman, L. Danos, and T. Markvart, Opt. Express, 2015, 23, A1528–A1532. 8. L. Danos and T. Markvart, Chem. Phys. Lett., 2010, 490, 194–199. 9. L. Danos, R. Greef, and T. Markvart, Thin Solid Films, 2008, 516, 7251–7255.

Authors : Nicolas Guth 1, Lucile Dumont 1, Julien Cardin 1, Florian Ehre 1, Christophe Labbé 1, Fabrice Gourbilleau 1, Marzia Carrada 2, Omar Ibrahim Elmi 3, O. Robbe 3, Tao Xu 4, D.Stiévenard 5
Affiliations : 1 CIMAP, CRNS/CEA/ENSICAEN/UNICAEN, 6 boulevard Maréchal Juin, 14050 Caen Cedex 4; 2 CEMES-CNRS, Université de Toulouse, 29 rue J. Marvig, 31055 Toulouse, France; 3 PHLAM, UMR8523, Université de Lille 1, 59652 Villeneuve d’Ascq Cedex, France; 4 Key Laboratory of Advanced Display and System Application, Shanghai University, 149 Yanchang Road, Shanghai 200072, People's Republic of China; 5 IEMN, UMR8520, Université de Lille1, 59652 Villeneuve d’Ascq Cedex, France

Resume : One of the solutions for improving the energy conversion efficiency of silicon solar cells (SC) consists of using a down-conversion (DC) layer. Thus, DC layers doped with Tb3 and Yb3 ions allow the emission of two IR photons (1.26 eV) for each absorbed UV ones (>2.58 eV) through a cooperative energy transfer between Tb3+ and Yb3+ ions. Since IR photons energy is more suited to the Si band gap energy (1.11 eV) of SC than the UV ones, conversion efficiency is increased while the photogenerated carriers thermalization is reduced. Succeeding to dope the SiNx antireflective layer with such a couple of ions is consequently a key challenge. Tb3+ -Yb3+ co-doped SiNx layers deposited by reactive co-sputtering approach show an internal DC conversion quantum efficiency as high as 200%. To increase the number of IR photons converted, different approaches have been carried out: (i) a multilayer approach based on alternative Tb and Yb doped sub-layers has been developed for tailoring the Tb3+ -Yb3+ coupling rate and improving the down-conversion efficiency, (ii) silver spherical- and triangle-shaped nanoparticles have been embedded in DC layer to enhance the effective rare earth ions absorption cross-section. Modeling of light-matter interactions coupled to experimental results achieved in such different structures will be presented. An increase of the number of IR photons emitted by the DC layer into the SC has been demonstrated, which is promising for a future efficient SC.

Perovskite II : Kyle Catchpole
Authors : Jarvist Moore Frost, Aron Walsh
Affiliations : University of Bath, United Kingdom

Resume : Hybrid halide perovskites have rich solid state physics. We have recently reported the rotational activity of the molecular cations [1] using a combination of first principles simulations and quasi-elastic neutron scattering. A key beneficial aspect of these materials is the extremely long-lived charge carriers. One unique feature of hybrid perovskites that may extend charge carrier lifetime is the Dresselhaus splitting (due to large spin orbit coupling) of the conduction band leading to a slightly indirect band gap [2]. This effect is driven by the crystal field present in the bulk material due to the built-in dipole of the cation, and the distortion of the lead-iodide octahedra. Another effect is the fluctuation of electrostatic potential due to disorder, which will segregate hole and electron populations and so reduce recombination [3]. Both of these effects are driven by dynamic disorder. We have extended our on lattice Monte-Carlo model StarryNight [4], which can simulate the dimensions of actual thin-film samples, to three dimensions. Analysis of the thermodynamic ensembles as a function of temperature reveal the transition from long-range (low temperature) to short-range (room temperature) domain structures. The electrostatic potential is reconstructed from dipole alignment, and used as an input to a statistical mechanical recombination model [5]. We quantify the beneficial decrease in recombination rate due to segregation of electrons and holes in the 'ferroelectric highways', versus the detrimental decrease in mobility due to disorder. Our new model quantifies the contribution of short-range ferroelectric order on carrier stability and electron-hole recombination in this unique class of materials. This work has benefited from funding by the EPSRC and close collaboration with the groups of Mark van Schilfgaarde (King's College London), Piers Barnes (Imperial College London), and Laurie M. Peter (University of Bath). 1. A. M. A. Leguy et al, Nature Comm. 6, 7134 (2015). 2. F. Brivio et al, Phys. Rev. B. 89, 155204 (2014). 3. J. M. Frost, K. T. Butler and A. Walsh, APL Mater. 2, 081506 (2014). 4. J. M. Frost 5. J. M. Frost (unpublished).

Authors : Narges Yaghoobi Nia1, Fabio Matteocci1, Aldo Di Carlo1
Affiliations : 1C.H.O.S.E. (Centre for Hybrid and Organic Solar Energy), Department of Electronic Engineering, University of Rome ‘‘Tor Vergata’’, via del Politecnico 1, Rome 00133, Italy.

Resume : CH3NH3PbI3-based perovskite solar cells (PSC) are an important class of photovoltaic devices with high efficiency, low cost and easily scale-up fabrication process. Among the different deposition processes introduced for PSC fabrication, the two-step method is easy to scale up for large area modules. In the two-step method, deposition of PbI2 layer is crucial because this layer can affect the nucleation process of perovskite. In the present work, we investigate the effect of dopants in PbI2 solution on the performance of PSCs. Different amounts of various dopants like dimethyl sulfoxide (DMSO), t-buthyl pyridine (TBP) and Li-salt are used in PbI2 solution containing dimethylformamide (DMF) as solvent. Furthermore, effect of PbI2 preheating process is also investigated in perovskite nucleation and crystal growth process. The effects of these variants are evaluated by UV-Vis, IV measurement and cyclic voltammetry and standard light and moisture stability test methods. The results show higher overall efficiency and stability of the devices containing small amounts of DMSO as dopant and cold dipping of PbI2 layer in methylammonium iodide solution.

Authors : M. Jošt1, S. Albrecht2, J. Krč1,L. Korte, B. Rech2, M. Topič1
Affiliations : 1University of Ljubljana, Faculty of Electrical Engineering, Tržaška 25, 1000 Ljubljana; 2Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Institut für Silizium-Photovoltaik, Kekuléstraße 5, 12489 Berlin, Germany.

Resume : Perovskite / silicon-heterojunction tandem solar cells are interesting candidates to exceed the Shockley-Queisser limit for single junction solar cells due to the complementary energy band gaps and the high conversion efficiency of the two subcells. Optical simulations have indeed shown the potential in both monolithic and 4-terminal configuration [1]; first experimentally realized devices also show promising results [2]. Currently, experimental monolithic tandem devices have planar configuration only and are therefore partially limited by non-optimal photocurrent generation, due to reflection losses and imbalance between the photocurrents generated in the two subcells. Further gains in photocurrents can be achieved by introducing structures for light scattering and anti-reflection (AR). However, commonly used random pyramid texturization of silicon wafers is not yet suitable for the deposition of thin perovskite layers when implementing deposition techniques such as spin coating that yield the highest efficiencies to date. An alternative way to reduce optical losses on planar wafers is utilizing UV Nanoimprint Lithography (UV NIL). With UV NIL an additional transparent textured layer on top of the planar tandem (or single junction) cell can be created that enables light scattering or/and AR. In our contribution, we focus on numerical modeling for the optical optimization of monolithic perovskite/silicon-heterojunction tandem solar cell using the optical simulator CROWM which is based on a combined ray and wave optics model [3]. First, random pyramids of the silicon wafer either at the back or on both sides are considered. Second, different textures, such as randomly and periodically distributed pyramids, concave microlenses and spheroidal shapes, deposited on the top of the flat tandem cell (ITO) by UV NIL process are investigated. For the selected device architectures we optimize the thickness of the perovskite layer to achieve current matching in monolithic perovskite/silicon-heterojunction tandem solar cells. We present the experimentally relevant optimization for the different thicknesses of recombination layer (ITO) and hole transporting layer (spiro-OMeTAD). Our simulations show that using UV NIL textured layers on top of the planar tandem cell, more than 2 mAcm 2 in photocurrent density can be gained and front reflection is strongly reduced. Finally, the suitability of this process will be shown by comparison of simulations and experiments for perovskite single junction solar cells with a top UV NIL layer. Thus, our results give insight into the light management improvements in perovskite single junction and perovskite/silicon tandem solar cells. Literature [1] M. Filipič, P. Löper, B. Niesen, S. De Wolf, J. Krč, C. Ballif, and M. Topič, “CH_3NH_3PbI_3 perovskite / silicon tandem solar cells: characterization based optical simulations,” Opt. Express, vol. 23, no. 7, p. A263, Apr. 2015. [2] S. Albrecht, M. Saliba, J. P. C. Baena, F. Lang, L. Kegelmann, M. Mews, L. Steier, A. Abate, J. Rappich, L. Korte, R. Schlatmann, M. K. Nazeeruddin, A. Hagfeldt, M. Grätzel, and B. Rech, “Monolithic perovskite/silicon-heterojunction tandem solar cells processed at low temperature,” Energy Environ. Sci., vol. 9, no. 1, pp. 81–88, Jan. 2016. [3] B. Lipovsek, J. Krč, and M. Topič, “Optical model for thin-film photovoltaic devices with large surface textures at the front side,” Inf. MIDEM, vol. 41, no. 4, pp. 264–271, Dec. 2011.

Authors : Thomas Dittrich, Oleksandra Shargaieva, Felix Lang, Jörg Rappich
Affiliations : Helmholtz - Zentrum Berlin für Materialien und Energie GmbH

Resume : One direct method for the measurement of the diffusion length of photogenerated charge carriers in semiconductors is based on the dependence on the absorption length of the intensity required for keeping a surface photovoltage (SPV) signal constant (Goodman 1961). Transport or diffusion lengths in CH3NH3PbI3 samples were measured with high accuracy by applying several SPV signals for each sample. Values of the transport lengths varied between tens of nm and µm depending on preparation and treatments. The reliability and the simplicity of the method allow its application also for in-line characterization under well controlled ambience.

Authors : P.M. Kaminski1, P.J.M. Isherwood1, G. Womack1,2, J.M. Walls1
Affiliations : 1CREST (Centre for Renewable Energy Systems and Technology), School of Electronic, Electrical and Systems Engineering, Loughborough University, Loughborough, LE11 3TU, United Kingdom 2National Structural Integrity Research Centre (NSIRC Ltd.), Granta Park, Great Abington, Cambridge, CB21 6AL, United Kingdom

Resume : High conversion efficiency has been recently demonstrated for Perovskite thin film photovoltaic devices. Perovskite thin film solar cells are multilayer opto-electrical structures in which light interference occurs. This phenomenon can be used to maximise the light transmission into the absorber material and increase the device efficiency. Fine tuning of the layer thicknesses within the stack can be used to control interference at the interfaces. Optical reflection losses can be reduced by achieving destructive interference within the structure of the cell. The light transmission to the Perovskite absorber of a thin film solar cell on a fluorine doped tin oxide transparent conductor has been modelled using the transfer matrix method. Alternative transparent conductor materials have been also investigated including AZO and ITO. The modelling showed that replacing FTO with ITO could increase the photocurrent by as much as 4.5%. The gain can be further increased to 6.5% by using AZO as the TCO material. Fine tuning of the TiO2 layer thickness can increase current by 0.3%. Furthermore, the current of a Perovskite solar cell can be increased by application of a multilayer anti-reflective coating by another 3.5%. Optical optimisation of the stack design offers a significant increase in conversion efficiency.

Poster session 1 : Selcuk Yerci, Ivan Gordon
Authors : P. Palacios¹, J.E. Castellanos Águila², J.C. Conesa, J. Arriaga, P. Wahnon
Affiliations : Instituto de Energía Solar (IES-UPM) and Dept. FAIAN, ETSI Aeronáutica y del Espacio, Universidad Politécnica de Madrid, Pz. Cardenal Cisneros, 3, 28040, Madrid, Spain; Instituto de Energía Solar (IES-UPM) and Instituto de Física, Benemérita Universidad Autónoma de Puebla, Av. San Claudio y 18 Sur, C.U. 72570 Puebla, México; Instituto de Catálisis y Petroleoquímica, CSIC, Marie Curie 2, Cantoblanco, 28049, Madrid; Instituto de Física, Benemérita Universidad Autónoma de Puebla, Av. San Claudio y 18 Sur, C.U. 72570 Puebla, México; Instituto de Energía Solar (IES-UPM) and Dept. TFO & Instituto de Energía Solar, ETSI Telecomunicación, Universidad Politécnica de Madrid, 28040 Madrid, Spain.

Resume : Chalcopyrite semiconductors are commonly used as materials on solar cell devices. Built as tandem solar cells, the study of the heterointerfaces between different semiconductors which are components of the devices should be crucial to understand their operation. Band alignments of the heterojunctions between CuGaS2 chalcopyrite and different semiconductors have been theoretically obtained using density functional theory with hybrid functionals. Band alignments have been determined using an average electrostatic potential as reference level. We have also studied the strain between the heterointerfaces which plays an important role in the electronic properties of them.Results show that CuAlSe2/CuGaS2 and CuGaS2/ZnSe heterointerfaces show band alignments where holes and electrons are localized on different sides of the heterojunction. This condition is necessary for their application on photovoltaic devices. If suitable transition metals are used to substitute for Gallium atom in the CuGaS 2 chalcopyrite, an intermediate band solar cell could be made, which could potentially improve the performance of a solar cell.

Authors : Mustafa Ünal(1),(2)*, Aydın Tankut(2), İlkay Sökmen(3), Tahir Çolakoğlu(2), Raşit Turan(1),(2)
Affiliations : (1) Department of Physics, Middle East Technical University, DumlupinarBlvrd no: 1, 06800, Ankara Turkey (2) The Center for Solar Energy Research and Applications (GÜNAM), Middle East Technical University, DumlupinarBlvrd no: 1, 06800, Ankara Turkey (3) Şişecam Science and Technology Center, Şişecam Str., No:2Çayırova, Kocaeli Turkey *Corresponding author: Phone: +90 507 714 1698; Fax: +90 312 210 7941; e-mail:

Resume : Thin film solar cell approach aims to reduce cost of solar electricity by reducing material usage. Due to the limited film thickness, maximizing the absorption of the solar radiation is considered to be crucial. Scattering of the light provides longer optical path inside the thin film; thus, absorption of light can be enhanced. Aluminum induced texturing (AIT) is a promising method to increase the efficiency of thin film solar cells by promoting the scattering of the transmitted light through glass substrate. There are various parameters affecting the final texture of the AIT glass, such as aluminum thickness, annealing time, annealing temperature, etching time, etc. In this study, we focus on the N2annealing step of the AITprocess. During annealing, aluminum reacts with SiO2 and forms c-Si clusters and Al2O3. The effect of glass composition has been reportedin literature.Here, we aim to investigate on the evolution of the Al/Al2O3 layer and elucidate on the chemical processes that occur during N2 annealing. For the annealing experiment, two different study is made. In one of them,600 °C is set as fixed and samples are annealed in N2 ambient at different durations. To monitor the chemical nature of the films, annealed samples were examined by depth resolved X-ray photoelectron spectroscope (XPS). Surface morphology of the annealed samples before and after the removal of the reaction products were studied using optical microscope,scanning electron microscope and atomic force microscope.The scattering behavior of the textured glass samples were studied by goniometric optical scatter instrument. In the second study, annealing made at different temperatures and different durations. Evaluation of layer is examined by scanning electron microscope in EDX mode and optical microscope. After removing reaction products from surface, all samples are investigated by goniometric optical scatter instrument, atomic force microscope and scanning electron microscope.

Authors : Mingqing Wang, Giovanni Altamura, and Kwang-Leong Choy*
Affiliations : UCL Institute for Materials Discovery, University College London (UCL), Roberts Building, Malet Place, London WC1E 7JE, United Kingdom. Corresponding author’s email:

Resume : Kesterite (CZTS) is a promising candidate for low-cost and high efficiency earth abundant, thin film solar cells. With the recent reported rapid improvement of the efficiency of CZTSSe solar cells, it is highly desirable to develop a deposition method that is compatible with low cost and scalable processing of kesterite thin film soalr cells towards commercialization. In our group, a non-vacuum, low cost and eco-friendly Electrostatic Spray Assisted Vapour Deposition (ESAVD) method has been adopted to produce CIGS and CZTSSe absorbers for thin film solar cells[1-2]. ESAVD is a promising method for industrialization due to its high deposition speed and close to unity deposition efficiency. In this work, DMSO with a good complex with metal salts was adopted as solvent for CZTSSe precursors to better control the composition in the ESAVD deposited absorber. In addition to the composition and crystallization of absorber, the interface between absorber and Mo glass also has significant influence on the device performance of CZTSSe solar cells. In order to improve the efficiency of ESAVD deposited CZTSSe solar cells, an ultrathin ZnO (circa 10 nm) layer was employed as an intermediate layer between CZTSSe and Mo back contact to avoid the direct contact between Mo and CZTSSe and reduce the decomposition of CZTSSe during the annealing process. XRF and EDX were used to characterize the chemical composition of CZTSSe before and after selenization, respectively. SEM and Raman results showed the improved absorber morphology and the reduced direct interfacial reaction between CZTSSe and Mo. The improvement of the CZTSSe/Mo interface due to the presence of the ZnO intermediate layer was also reflected in the quality of the derived photovoltaic devices, leading to an improved efficiency of ESAVD deposited kesterite solar cells from 3.25% to 4.03%. Different alkali metals like Na, Li and Rb were incorporated into CZTSSe compounds to further improve the photovoltaic performances of the related devices. Photovoltaic properties results showed that Li, Na and Rb incorporation could increase the power conversion efficiency of CZTS devices up to 5.5%. The introduction of a thiourea treatment, has improved the quality of the absorber| buffer interface, and pushed the device efficiency up to 6.3% which is at the moment the best reported result for ESAVD deposited CZTSSe solar cells. References: [1] Giovanni Altamura, Mingqing Wang, Kwang-Leong Choy,Thin Solid Films(acceptted) [2] Mingqing Wang, Xianghui Hou, Junpeng Liu, KwangLeong Choy*, Paul Gibson, Elhamali Salem,Demosthenes Koutsogeorgis, and Wayne Cranton, Phys. Status Solidi A 212, No. 1, 72–75 (2015). Acknowledgements: This work has been funded by the European Union’s Seventh Framework Programme Scalenano, FP7/2007-2013 under grant agreement nº 284486.

Authors : M.Fedina^1, H.-P. Komsa^1, V. Havu^1, M.Puska^1
Affiliations : 1. COMP, Department of Applied Physics, Aalto University, POBox 11100, FI-00076 Aalto, Finland

Resume : During the last years, the research on Cu(In,Ga)Se2 (CIGS) as a promising absorber candidate for low-cost thin-film photovoltaic cells has steadily increased widening our understanding on its basic materials properties [1] and leading to a high efficiency of 21.7 % for the solar cells [2]. The defect microstructure influences optical and electronic properties of the material. Understanding its evolution during the manufacture and use of solar cells is impossible without knowing the fundamental parameters of its native point defects, the most important one of which is the defect formation energy. Indeed, there exist several recent first-principles studies [3-7] for defect formation energies in CuInSe2 (CIS) and CuGaSe2 (CGS). Their results agree with respect to general trends and orders of magnitudes, but they may differ in some important cases resulting, e.g., in different values for ionization levels within the band gap. It may be even so that some ionization levels arise only in part of the published calculations. Because these details are important in predicting the influence of the defects on doping and charge carrier compensation in the material this kind of discrepancies should be solved. A possible reason for the situation could be the use of inappropriate or insufficient computational parameters and post – treatments. We present the results of a detailed systematic study on the influence of computational parameters on the formation energies. Our approach is based on comparing results obtained by different existing corrections for the supercell method and by different electronic-structure calculation schemes (Projector-augmented wave – plane-wave method, All-electron – numerical-atomic-orbitals method). Another aspect of this presentation is the influence of alkali metal impurities. During the thin film deposition, sodium and potassium diffuse into the CIGS layer [7] and they have also been subjects of several first-principles investigations [8-10]. Inspired by the scatter in the first-principles results for native defects in CIGS materials we have revisited also the formation and migration energies of alkali metals as well as their clustering with other defects. Also we calculated migration barrier for defect in Cu-poor compounds. The migration barriers were determined by the state-of-the-art climbing-image nudged-elastic-band (CI-NEB) method for different types of materials, such as the stoichiometric CIS and the Cu-poor ordered compound. References: [1] Susanne Siebentritt et al.  Solar Energy Materials and Solar Cells,119, 18 (2013). [2]Michael Powalla, Wolfram Witte, Philip Jackson, Stefan Paetel, Erwin Lotter IEEE, Journal of Photovoltaics 4(1):440 (2014). [3] Yu Kumagai and Fumiyasu Oba Phys. Rev. B 89, 195205 (2014) . [4] J. Pohl and K. Albe, Phys. Rev. B 87, 245203 (2013). [5] L. E. Oikkonen, M. G. Ganchenkova, A. P. Seitsonen, and R. M. Nieminen, Phys. Rev. B 86, 165115 (2012); ibid. J. Phys.: Condens. Matter 26 345501 (2014). [6] J. Bekaert,   R. Saniz   B. Partoens Phys. Chem. Chem. Phys., 2014,16, 22299-22308 (2014). [7] F. Pianezzi, P. Reinhard, A. Chirilă. Appl. Phys. 114, 194508 (2013). [8] Tsuyoshi Maeda, Atsuhito Kawabata, and Takahiro Wada Japanese Journal of Applied Physics 54, 08KC20 (2015). [9] L. E. Oikkonen, M. G. Ganchenkova, A. P. Seitsonen, and R. M. Nieminen, J. Appl. Phys 114, 083503 (2013). [10] E.Ghorbani, Janos Kiss, Thomas Gruhn, Guido Roma J. Phys. Chem. C, 2015, 119 (45), pp 25197–25203 (2015).

Authors : Aline Cristiane Pan, Leandro Santos Grassi Cardoso, Fernando Soares dos Reis
Affiliations : Solar Energy Technology Nucleus (NT-Solar), Pontifical Catholic University of Rio Grande do Sul, Av. Ipiranga, 6681, Porto Alegre, Cep: 90619-900, RS – Brazil

Resume : Up-Converters implemented in solar cells have theoretical efficiencies of the conversion much higher than the actual and a much smaller price production price. However, the experimental results in the present do not approach the theoretical calculated values, because they have a small increase in photocurrent by incorporating the bifacial solar cell, for example. Hence, it is necessary dispose a quantitative tool for the characterization of candidate materials as up-converter, which permits realize an influence sensibility analyzes of certain parameters and contrasts with the real values founded. Thus, the fundamental objective of this work is to develop a mathematical model to study the behavior of up-converters, based on real parameters found in the literature, when implemented in silicon bifacial solar cells. Besides, exemplifies this model getting comparative results (I x V curve) for different materials used as up-converter when incorporated in silicon bifacial solar cells using the unidimensional software, PC1-D, in order to get the best candidates to be used.

Authors : Aline Cristiane Pan, Leandro Santos Grassi Cardoso, Guilherme Torres Marques Vidal, Jennifer Cláudia Passos Teixeira, Joaquim F. M. C. Pratas Leitão
Affiliations : Solar Energy Technology Nucleus (NT-Solar), Pontifical Catholic University of Rio Grande do Sul, Av. Ipiranga, 6681, Porto Alegre, Cep: 90619-900, RS – Brazil

Resume : Combine lower production costs with high efficiency currently it has been a major challenge for the development of solar cells. Then, the objective for this work is to study of optical performance of commercial up converters and quantum dots for application in bifacial solar cells. These materials have properties of absorbing infrared radiation and re-emit visible radiation, and thus the bifacial solar cells can improve the efficiency of solar cell. 24 samples is prepared in a silicone gel, similar to that used in the encapsulation of solar cells for photovoltaic module of the composition, with different concentrations of up converters and quantum dots. To study the performance optical of commercial up converters and quantum dots used the reflectance, transmittance and photoluminesce. PTIR545/UF from Phosphor Tecnology converter showed the most promising results, mainly associated with quantum dots. For exhibit considerable reduction in transmittance and an excellent absortance for wavelengths where the solar cell does not respond. The three measurements indicate similar characteristics of the quantum dots and up converters demonstrating the veracity of the proposal characterization.

Authors : H. Saïdi, M. F. Boujmil and M. Bouaïcha*
Affiliations : Laboratoire de Photovoltaïque, Centre de Recherches et des Technologies de l’Energie, Technopole de Borj-Cédria, BP 95, Hammam-Lif, 2050 Tunis, Tunisia

Resume : CuInSe2 nanoparticules (CIS-NP) were synthesized on ITO-coated glass substrate by electrodeposition and rapid thermal processing (RTP). The as-deposited films were annealed under argon atmosphere at 250°C, 350°C and 450ºC using RTP for a short time. The relatively short annealing time is proved to be practicable to avoid further losing of the Se content in CIS films. In order to analyze the effect of annealing temperature, the structural, morphological, optical and electrical properties were investigated respectively by means of Xray diffraction, scanning electron microscopy, UV-Visible Spectroscopy and Mott-Schottky plots. XRD results show that elaborated films have a tetragonal chalcopyrite CIS with preferential orientation along (112) orientation. The phase formation of the CIS with good crystallinity was observed at low annealing temperature. Optical absorption studies indicate a direct band gap around 1.02 eV at 250 °C. The optical constants such as refractive index n(λ) and extinction coefficient k(λ) were estimated using an appropriate optical model. To determine the doping type of elaborated semiconductor, its flat band potential and the free carrier concentration we have used the Mott-Schottky plots. A new attempt to anneal the electrodeposited CIS films by short annealing duration using RTP process was proved to be a useful method to synthesize polycrystalline CIS films for solar cell application.

Authors : Md. Imteyaz Ahmad (1), Jeremy D Fields (2), Vanessa L Pool (1), Jiafan Yu (1), Douglas Van Campen (1), Philip A Parilla (2), Maikel FAM van Hest (2), Michael F Toney (1)
Affiliations : 1 Stanford Synchrotron Radiation Lightsource (SSRL), SLAC National Accelerator Laboratory, Menlo Park, CA 94025 2 National Renewable Energy Laboratory (NREL), Golden, CO 80401

Resume : Screen-printing provides an economically attractive means for making silver electrical contacts to silicon solar cells, but the use of silver substantiates a significant manufacturing cost, and the glass frit paste used in contact formation contains lead. This front contact metallization of Si begins with printing a mixture of an Ag powder, glass frit (mixture of metal oxides such as PbO, SiO2, B2O3, and Bi2O3) and an organic binder over the antireflection coating that is subsequently rapidly fired (<10 secs) up to about 800 ºC. It is known that the frit allows the paste to react with and burn through the anti-reflective coating such that the metal can react with the underlying c-Si during firing. However, the precise phase transformations between Ag, Si, SiNx, and the frit constituents, which happens within few seconds during rapid thermal processing (RTP), giving rise to an Ag-Si contact, are not well understood in absence of in-situ characterization under the actual processing conditions. We have carried out in-situ x-ray diffraction studies on sample mixtures of different components powders (Ag, SiNx, PbO-frit and Si) under realistic processing conditions using an in-situ rapid thermal processing setup. We track the phase progression and reaction pathways at a time resolution of 100 milliseconds. We show the direct evidence of SiNx oxidation by PbO between 550-650 C. On subsequent heating to higher temperature, up to 800 ºC, Ag dissolves into the frit in the form of Ag+ ions, which subsequently etch the c-Si surface and are deposited on etch pits forming intimate electrical contacts. On cooling Ag nanocrystals precipitate in the glass frit allowing electrical contact to the Si. This work clarifies contact formation mechanisms and suggests approaches for development of inexpensive, nontoxic solar cell contacting pastes.

Authors : Marouan Khalifa, Malek Atyaoui, Messaoud Hajji, Hatem Ezzaouia
Affiliations : Semiconductor and Advanced Technology Nanostructured Laboratory. Research and Technology Centre on Energy , Borj-Cedria Science and Technology Park, BP 95, 2050 Hammam-Lif, Tunisia Higher Institute of Electronics and Communication in Sfax, Route MenzelChaker, 0.5km Sfax, BP 868 3018, Tunisia

Resume : The Porous Silicon layers were formed on p-type silicon wafers by electrochemical etching in an HF:C2H5OH (1:1 by volume) electrolyte at room temperature at a constant current density 20mA/cm2 and etching duration 5min. This paper investigates the effect of Berberine on the passivation of PS. The immersion of as-etched PS in dilute Berberine solution. The immersion duration of berbrine was variable from 5 to 20min. For the optical and morphological characterization of porous films, Photoluminescence spectroscopy, FTIR spectroscopy and Reflectivity spectroscopy were used. A decrease in the reflectivity to about 6% for Berberine/PS annealed at 20minwas obtained. From Photoluminescence (PL) spectra, a blue-shift of the gap and an intensity were observed when the immersion duration is increased to 20min; we correlate these results to the change in chemical composition of the layers in order to find the optimized conditions for a potential application in silicon solar cells.

Authors : T. Slimani Tlemçani1, E.B. Benamar1, M. Sekkati1, M. Taibi2, G. Schmerber3, Z. Sekkat1,4, A. Dinia3, A. Slaoui5 and M. Abd-Lefdil1
Affiliations : 1Mohammed V University, Materials Physics Laboratory, P.B. 1014, Rabat - Morocco; 2Mohammed V University, LPCMIO, Ecole Normale Supérieure Rabat- Morocco; 3Institut de Physique et Chimie des Matériaux de Strasbourg, Université de Strasbourg, CNRS UMR 7504, 23 rue du Loess, B.P. 43, F-67034 Strasbourg Cedex 2, France; 4Moroccan Foundation for Advanced Science, Innovation and Research, MAScIR, Optics & Photonics Center, Morocco; 5ICube UMR 7357, 23 rue du Loess - BP 20 CR - 67037 Strasbourg Cedex 2, France

Resume : Cu2ZnSnS4 (CZTS) thin films were successfully deposited on soda lime as well as on molybdenum coated soda lime glass substrates by ultrasonic spray technique. After sulfurization treatment under Argon atmosphere at 500°C, the films were polycrystalline and exhibited the kesterite structure which was confirmed by X-ray diffraction and Raman spectroscopy. The composition, surface morphology and optical properties were examined by dispersive X-ray spectroscopy, scanning electron microscopy and photoluminescence spectroscopy respectively. By Hall effect measurements, electrical resistivity and Hall mobility of about 2.4 10-1 and 6 cm2•V−1•s−1 were reached respectively. Keywords: Cu2ZnSnS4, thin films, ultrasonic Spray process, sulfurization.

Authors : M.A. Jafarov, E.F. Nasirov, S.A.Jahangirova
Affiliations : Baku State University, Baku, Azerbaijan,

Resume : The semiconductor compound Cu2Zn1-xCdXSnS4 (CZCTS) is considered as one of the ideal photovoltaic absorber layer materials for low-cost thin film solar cells, since CZCTS has a large absorption coefficient and all the constituent elements are naturally abundant. A Cu2Zn1-xCdXSnS4 (CZCTS) thin films system (where x = 0 and 0.2) are deposited using chemical bath deposition method on the alluminium and İTO glass substrates.The films deposited onto İTO-glass slides were first cleaned with detergent water and then dipped in acetone. Solution were prepared by mixing 0.2 M aqueous solutions of CuCl2, ZnCl2, CdCl2, SnCl4, and thiourea [CS(NH2)2] at ratio of 2x:1-x: x: 1: 4 (Cu,Zn,Cd,Sn,S) using a magnetic stirrer. The films had a uniform thickness of (800) nm. the structural properties were determined by X-ray diffraction (XRD; Shimadzu) with CuKα radiation (λ = 1.5406 Å). Film morphology was analyzed by atomic force microscope (AFM)- type (CSPM). The optical absorption and transmission spectra were obtained using a UV-vis spectrophotometer within the wavelength range of 300 nm to 1100 nm. The XRD patterns show the major diffraction peaks at 2θ= (28.59) and (28.4) for CZTS at x = 0 and for CZCTS at x = 0.2. The increase in cadmium (Cd) as shown by the shift in the main diffraction peak to a lower value of 2θ is attributed to the increase in lattice spacing of the longer Zn atom (1.71 A°) substation for smaller Cd atoms (1.53 A°). Furthermore, an increase in the main peak intensity is observed in the presence of cadmium. A comparison with ASTM card JSPDS 26-0575 reveals that the CZTS (x = 0) thin film exhibits a crystal structure tetragonal type of kestrits phase with a preferred orientation (112) and other planes, i.e., (220) and (312). For 2θ= (28.59, 47.5, 56.1 The CZCTS film at x=0.2 has a tetragonal phase. The absorbance layers of CZCTS were measured from 300nm to 1100nm. Shows the plot of α (cm-1) versus the wave length λ, which suggests that the two Film exhibits high absorption coefficient ( > 104 cm-1). Thus a very thin layer of film (1-2μm) can absorb over 90% of photons over the spectrum, with higher photon energy in the bandgap. The optical properties of the CZTS layer can be improved with a substitution of Zn atoms by Cd atoms to give lower energy gap gap, because since ZnS has a direct optical band near 3.6 eV that gives a higher energy gap of CZTS. The absorption edge shifts to the NIR region with increased x. The obtained optical gap for CZTS is (1.7)eV which agrees with the CZTS bandgap and 1.66 eV for CZCTS at x = 0.2. Eg decreases with increased cadmium content. The CZCTS films coated on Al substrates were applied to the preparation of CZCTS solar cells. The CZCTS solar cells with a structure of Al /ZnO/CdS/ CZCTS /İn lime glass were fabricated. The performance of the solar cells was evaluated under standard AM 1.5 (100mW/cm2) illumination. The solar cell with the CZCTS absorber layer annealed at 3000C, exhibited a relatively high efficiency of 9.2% (Voc - 0,520 V, Jsc – 22,4 mA/cm2, FF – 0,65). It confirms the effect of preventing the decomposition of CZCTS phase by the addition of Sn during the annealing process. In conclusion, a simple and relatively safe approach for the fabrication of CZCTS nanoparticles has been developed. To the best of our knowledge, this is the first time that this low-temperature colloid approach has been applied to the fabrication of CZCTS nanoparticles. We found that the use of different chalcogenide sources resulted in different products of synthesis. The annealing temperature and special ambient effect on the properties of CZCTS films were investigated.

Authors : Idriss Abdoulkader Ibrahim, Abderrhamane Belkhir, Ali Ali Nouho, Fadi Issam Baida
Affiliations : Université de Djibouti, Faculté d'Ingenieurs, Avenue Djanaleh, BP 1904, Djibouti.Université de Mouloud Mammeri,Laboratoire de Physique et Chimie Quantique UMMTO 15000 Tizi-Ouzou, Algérie.Université de Djibouti, Centre de Recherche de l’Université de Djibouti, Avenue Djanaleh, BP 1904, Djibouti. Institut FEMTO-ST, UMR 6174 CNRS, Département d’Optique P. M. Duffieux, Université de Franche–Comté, 25030 Besançon Cedex, France.

Resume : Using finite-difference-time-domain (3D-FDTD), we investigate the use of a periodic array of nanocoax within a thin amorphous silicon (a-Si) supported on the glass superstrate (n=1,5), to enhance optical light absorption allowing it to be used in photovoltaic application. In this analysis, the results reveal that the absorption through the coax design is insensitive to the incident and azimutal angle. We evaluate the performance of coax as a function of the normal and oblique incidences of light. By using nanocoax apertures, we have found the way to reduce the thickness of semiconductor film without losing the extraordinary absorption.The aim of this study is to demonstrate that the nanocoax apertures engraved in silicon film, improves the efficiency of absorption light for solar applications. Its insensitive behavior to the azimutal and incident angles and its polarization-insensitive from the light brings a new concept for plasmonic metamaterial engraved in photovoltaic cell for increasing the light absorption. These results are promising for the design of solar cells with nanocoax giving extraordinary absorption.

Authors : Nicholas Goffin, Fabiana Lisco, Gianfranco Claudio, John Tyrer, Elliot Woolley
Affiliations : Nicholas Goffin,Elliot Woolley: Centre for Sustainable Manufacturing and Recycling Technologies (SMART), Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, LE11 3TU, UK; Fabiana Lisco, Gianfranco Claudio: Centre for Renewable Energy Systems Technology (CREST), School of Electronic, Electrical and Systems Engineering, Loughborough University, Leicestershire, LE11 3TU, UK; John Tyrer: Optical Engineering Research Group, Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, LE11 3TU, UK

Resume : CdTe-based thin film solar cells currently represent one of the fastest growing PV technologies, with a superior combination of efficiency, energy payback time and lifecycle environmental impact. However, the current post-deposition annealing treatment is still an energy intensive step of the manufacturing process. A novel method is presented for annealing of CdTe using a high-power diode laser (35 W, 808 nm) for thermal post-processing, combined with holographic optical elements (HOE’s) for laser beam heat flow control. The advantage of a laser for annealing lies in its ability to selectively heat only the surface of the CdTe solar cell; improving energy efficiency, process speed and energy resilience. Heat transfer simulations were used to predict the effects of different laser irradiance profiles on the annealing process thermal cycle, influence the experimental design and predict optimal laser irradiance profiles. Variations in power and process speed on as-deposited and MgCl2-treated close-space sublimated (CSS) CdTe samples have been performed. The results were characterised using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Optical properties were analysed with a spectrophotometer and ellipsometric spectroscopy (SE). The laser annealing treatment was found to be effective in promoting Chlorine diffusion and improving the optical and morphological properties of CdTe thin film devices.

Authors : Mathilde Schoenauer Sebag, Lionel Aigouy, Zhuoying Chen
Affiliations : Laboratoire LPEM, UPR A0005 CNRS / UPMC, ESPCI, 10 rue Vauquelin 75231 Paris Cedex 5, France

Resume : To response to the world’s urgent need of sustainable energy production, photovoltaic devices, converting the energy of sunlight into electricity, represent one of the most promising avenues. In the search for cost-effective solar cells, solution-processable third-generation solar cells based on organic conjugated materials or organic-inorganic hybrid perovskites are key candidates, currently yielding power-conversion efficiencies of more than 20%. However, many of these organic and hybrid perovskite solar cells can harvest photons from the visible up to only about 800 nm. More than half of the energy of the solar spectrum (in the near-IR) cannot be absorbed. On this issue, lanthanide-doped fluoride upconversion (UC) nanocrystals (e.g. lanthanide-doped NaYF4), if properly incorporated in to the solar cell structure, can be a promising approach to harvest near-IR photons. Such UC process can be further boosted by plasmonic structures. In this work, we perform colloidal synthesis on lanthanide-doped NaYF4 nanocyrstals of different compositions. On solar cells based on methylammonium lead trihalide perovskites, we experimented different strategies to incorporate UC nanocrystals, plasmonic nanostructures, and/or both into the device architecture. Their impacts on the device performance and in particular on near-IR light harvesting will be discussed.

Authors : Malek Atyaoui 1, Aetf Atyaoui 2, Marwen Khalifa 1 , Jalel Elyagoubi1, Marwen Khalifa 1 Wissem Dimassi 1and Hatem Ezzaouia
Affiliations : (1) Laboratoire de Photovoltaïque, Centre des recherches et des technologies de l’énergie, technopole de Borj-Cédria, PB :95,Hammam Lif 2050, Tunisia (2) Office national des mines, Ministère de l’industrie, de l’énergie et des mines, Tunisia

Resume : The surface Plasmon effect of noble metal nanoparticles on the photovoltaic properties of silicon solar cells was investigated. The metal nanoparticles were deposited on the p-type silicon base of the n+/p junction using a chemical deposition method followed by a thermal treatment at 500°C under nitrogen atmosphere. Chemical composition and surface morphology of the deposited metal were examined by energy dispersive X-ray (EDX) spectroscopy and scanning electronic microscopy (SEM). The effect of the deposited nanoparticles on the electrical properties was evaluated by the internal quantum efficiency (IQE) and current-voltage (I-V) measurements. The results indicate that the formation of the metal nanoparticles is accompanied by an enhanced light absorption and improved photovoltaic parameters.

Authors : Tao Xu1, Omar Ibrahim Elmi2, O. Robbe2, C. Krzeminski3 and D.Stiévenard3
Affiliations : 1: Key Laboratory of Advanced Display and System Application, Shanghai University, 149 Yanchang Road, Shanghai 200072, People's Republic of China 2: PHLAM, UMR8523, Université de Lille 1, 59652 Villeneuve d’Asq Cédex, France 3: IEMN, UMR8520, Université de Lille1, 59652 Villeneuve d’Ascq Cédex, France

Resume : The light absorption of planar(Pl) junctions can be improved using nanostructured top surfaces due to their enhanced light trapping properties. Nevertheless, associated with the higher nano-textured surface, the concentration of the recombination surface centers increases, leading to electrical performance degradation. We present comparative studies of the electrical yield of planar and nanostructured solar cells, passivated by SiNx-H or Al2O3 layers. Firstly we realized n - p junctions using (180 keV, 1018 cm-3) implantation of phosphorous in 2x1015 cm-3 boron p type silicon material. Monte Carlo simulation was first performed to optimize the junction profile for nanostructured surface. SIMS analysis are in agreement with the simulations. Dense and uniform arrays of silicon based nanopillars (NPs) and nanocones (NCs) were fabricated by self-assembled silica particles as etch masks. The reflectivity of the Pl, NPs and NCs surface decreases typically by a factor of 3 from 350 to 800 nm, the best one being associated with NCs. SiNx:H and Al2O3 passivation layers increase the electrical yield of the cells typically by a factor of 2 and 6 respectively. The best result is obtained for NPs based cells with a 5 % yield. Efficiency of the passivation layers is discussed versus the morphology of the surfaces. Acknowledgments: This work was partly supported the “GENESE” contract (Ref: 13-BS09-0020-03) from the Agence Nationale de la Recherche, ANR, . T. Xu acknowledges support from the National Natural Science Foundation of China (61204014).

Authors : Salar Habibpur Sedani, Rasit Turan, Ozlen Ferruh Erdem
Affiliations : Center for Solar Energy Research and Applications, METU, Turkey, Micro and Nanotechnologies Graduate Program, METU, Turkey; Center for Solar Energy Research and Applications, METU, Turkey, Department of Physics, METU, Turkey; Center for Solar Energy Research and Applications, METU, Turkey, Department of Physics, METU, Turkey

Resume : Boron and phosphorous doped thin film Si solar cells were prepared by (effusion cell equipped) electron beam evaporation method. Doping levels, crystallization conditions, and the point defect centres were investigated by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS), electrical properties measurements, Raman Spectroscopy, X-Ray Diffractometer, and temperature dependent electron paramagnetic resonance (EPR) spectroscopy. Especially, EPR spectroscopy gives detailed information about the electronic state of the paramagnetic system, point defect centres in Si-based photovoltaic semiconductor solar cells [1,2], changes in the crystal symmetry (reflected in the Landé g factor of the conduction electrons) [3], hyperfine interaction of the unpaired electron with nearby nuclei, etc. By means of X-band EPR characterization at different microwave powers, it was shown that, upon transition from amorphous to polycrystalline, the nature of the defect centres change from delocalized-like (with fast relaxation) to localized-like (with slow relaxation) electron behaviour. Both room temperature and low temperature (10-70K) measurements revealed crucial information about the changes in the electronic structure depending on the substrate, type of doping, and doping level which will help to construct solar cells with improved efficiency. [1] M. Jivanescu, A. Stesmans, and M. Zacharias, Journal of Applied Physics 104 (2008) 103518. [2] O. Astakhov, R. Carius, Yu. Petrusenko, V. Borysenko, D. Barankov, and F. Finger, Phys. Stat. Sol., 2 (2007) R77–R79. [3] G. Hendorfer and J. Schneider, Semicond. Sci. Technol. 6 (1991) 595-601.

Authors : Alexandra Szemjonov 1, Frédéric Labat 1, Ilaria Ciofini 1, Sandrine Ithurria 2, Nicolas Lequeux 2, Benoit Dubertret 2, Thierry Pauporté 1
Affiliations : 1 Chimie ParisTech, PSL Research University, CNRS, Institut de Recherche de Chimie Paris (IRCP), 11 Rue Pierre et Marie Curie, F-75005 Paris, France; 2 Laboratoire de Physique et d’Etude des Matériaux, UMR 8213 du CNRS, ESPCI, 10 rue Vauquelin, 75231 Paris, France

Resume : Due to their controlled band gap, quasi two dimensional CdSe nanoplatelets (NPLs) are interesting alternatives to spherical quantum dots (QDs) as sensitizers in quantum dot solar cells (QDSCs). Also, from a modeling point of view, their well-defined thickness can provide a good base for building stacked models and establishing direct links between experiment and theory. In this study, we combine theoretical and experimental methods to analyse a lattice-mismatched NPL-oxide heterostructure. Experimentally, CdSe NPLs of different thicknesses have been linked to hydrothermally grown ZnO nanorods by SH- ligands. These systems were characterized by SEM, Raman and UV-VIS spectroscopy. The results confirm the presence of NPLs on the substrate, and suggest significant structural changes upon the interface formation between them. The latter was confirmed by a theoretical analysis using a low-cost and highly accurate periodic density functional theory-based computational method. We also calculated the vibrational and electronic properties of this system, and the electron injection efficiency from the NPL towards the ZnO surface. The photogenerated charge transfer, in line with the working principle of QDSCs, turned out to be favored, but only partial. The proposed combined experimental/theoretical approach should be applicable for other semiconductor heterostructures in a wide range of photovoltaic devices to help rationalize their operating principles and thus design new systems.

Authors : C.Y. Tsai, C.T. Liang, H.R. Chen, and Y.C. Chang
Affiliations : Research Center for Applied Sciences, Academic Sinica, Taipei, 11529, Taiwan; Research Center for Applied Sciences, Academic Sinica, Taipei, 11529, Taiwan; Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, 1001 Tahsueh Rd., Hsinchu 300, Taiwan; Research Center for Applied Sciences, Academic Sinica, Taipei, 11529, Taiwan

Resume : Metal-semiconductor Schottky diodes provide a way to separate photo-generated electron-hole pairs near the Schottky junction, which may be useful for collecting solar energy. These photo-excited electrons in metal can travel ballistically over or tunnel through the Schottky barrier into semiconductor to produce currents, which are respectively known as internal photo-emission (IPE) and field-emission (FE). The transport characteristics of these carriers are investigated in an Au-TiO2 Schottky diode via I-V measurements under photo illumination from visible to ultraviolet (UV). Based on the effective-mass approximation modeling, the IPE injected carrier concentration is related to the forward current and short current enhancements comparing to those in dark condition. An external bias can modify the IPE carrier concentration by tuning the available density of states in TiO2 for the hot carriers in Au to inject into. The FE injection becomes important under reverse bias. By fitting the I-V curves according to the WKB approximation, the estimated Schottky barrier height decreases nonlinearly as excitation power increases, which is significant under UV light illumination. The quick recovery of reverse current at the termination of irradiation indicates that the FE process is strongly assisted by the photo-excitation. The fast conversion between rectifying and ohmic behaviors may find applications in optically controlled electronic switches.

Authors : Suresh Kumar, Bharath Kasubosula, Mihkel Loorits, Valdek Mikli, Mare Altosaar, Maarja Grossberg
Affiliations : Tallinn University of Technology, Institute of Materials Science Ehitajate tee 5, 19086, Tallinn, Estonia

Resume : Solution based dip coating method was used to deposit Cu2ZnSnS4 thin films on Mo and/or ITO covered or bare glass substrates. The influence of pre-annealing and post annealing temperature as well as the influence of used substrate on the morphology, phase composition and elemental composition of the resulting films was studied. Copper (II) Chloride, Zinc Chloride, Tin (II) Chloride and Thiourea were used as precursors for synthesis of Cu2ZnSnS4 (CZTS) in methanol as solvent. Thin films were produced by repeated dipping of substrates into gelled precursor solution. The films were dried at 75oC and annealed in two steps. Pre-annealing of dried as-deposited thin films was performed at various temperatures (180oC, 210oC, 240oC, 270oC and 300oC) in air, nitrogen atmosphere and in sealed vacuum ampoules. Post annealing was done in sealed vacuum ampoules at 550oC. Thin films pre-annealed at 240oC had near-stoichiometric elemental composition while rest of the films showed different deviations from stoichiometric CZTS. Thin films deposited onto Mo and ITO substrates were more close to the stoichiometric CZTS than the films on glass substrates, probably due to more effective adhesion of metal thiourea complex gel with Mo and ITO substrates. The thickness of one time dipped, dried and annealed film was found to be around 300 nm. Raman spectra and EDS analyses of the thin films deposited onto Mo substrate pre-annealed at 240oC and heated at 550oC showed Raman dominating peak at 337 cm-1 which corresponds to Cu2ZnSnS4 and a composition close to the stoichiometric composition of Cu2ZnSnS4.

Authors : Hasan Huseyin Gullu1-2, Mehmet Parlak1-2
Affiliations : 1. Department of Physics, Middle East Technical University (METU), Ankara 06800, Turkey 2. Center for Solar Energy Research and Applications (GÜNAM), METU, Ankara 06800, Turkey

Resume : II-VI compounds have been of great interest to both the research and commercial solar cell applications because of their many advantageous properties in optoelectronic and photovoltaic technologies. In this family, CdS and ZnSe are the most popular n-type layer in semiconductor device applications. However, toxic risks of CdS causes environmental concerns in the large scale solar cell applications due to usage of Cd. Moreover, for ZnSe films, the nature of the defects in the structure, and common high resistivity problem obstruct their photovoltaic applications. Alloying polycrystalline wide band gap thin film semiconductors with elements in group III is a familiar application to optimize the resistivity of these materials. Among these, ZnInSe2 (ZIS) ternary semiconductors have been researched in various fields. In this work, the device properties of the fabricated n-ZIS/p-Si junction were analyzed in detail. This hetero-junction diode was fabricated by physical vapor deposition by using (111) mono-crystalline 600 μm Si wafers with the resistivity value of 1 - 3 (Ω.cm). Initially, the structural, optical and electrical properties of the ZIS thin film layer deposited on the soda lime glass substrate were analyzed. Then, detailed electrical characterization of the hetero-junction was performed by the help of temperature dependent current-voltage (I-V) measurements. The forward I-V behavior of the hetero-junction diode was investigated under the two possible current transport mechanism as thermionic emission and space charge limited current, in addition to determining basic device parameters from the ohmic region. The reverse I-V characteristics of the junction were found to be dominated by tunneling characteristic. The contribution of the p- and n-layer in the junction was studied under the spectral photo-response measurement.

Authors : Tsubasa Nakamura(1), Kouki Matsuochi(1), Takumi Murakami(1), Hidetoshi Suzuki(1), Tetsuo Ikari(1), Kasidit Toprasertpong(2), Masakazu Sugiyama(2), Yoshiaki Nakano(3), and Atsuhiko Fukuyama(1)
Affiliations : 1 Faculty of Engineering, University of Miyazaki, Japan 2 School of Engineering, The University of Tokyo, Japan 3 Research Center for Advanced Science and Technology, The University of Tokyo, Japan

Resume : The insertion of a superlattice (SL) structure in the absorbing layer of solar cell is paid attention for increasing more the conversion efficiency. Since, the built-in electric field in the SL structure disturbs the miniband formation and increases the carrier recombination, we investigated these effects by using a photoreflectance (PR) and a photoluminescence (PL) spectroscopies. We prepared two kinds of samples with different built-in electric field. The SL structures were both inserted in the i-layer of p-i-n GaAs solar cell samples and the n-layer of n-n GaAs structure samples. The barrier thicknesses were changed from 2 to 6 nm for discussing the miniband formation in more detail. For the PR modulus spectra, two critical energies were observed at 1.27 and 1.31 eV. We have already reported the peaks of low and high critical energies are due to the Γ and π point of miniband edges, respectively. However, the obtained miniband widths were smaller than the calculated value by a transfer-matrix method. This is because the built-in electric field in the SL structure disturbs the wave function overlap between the adjacent wells. On the other hand, we observed a peak around 1.30 eV from the PL spectra for all samples. This peak shifted to the low energy side as the barrier width became thinner. Since the PL peak energy corresponds to the energy at the Γ point in the miniband, this shift is explained by the expansion of the miniband width. At the same time, the PL intensity decreased with decreasing the barrier width. Supposing that the carriers are transported mainly by tunneling though the miniband in the SL structure, this is attributed to the increase of non-radiative recombination probability.

Authors : Z. Hájková 1, M. Ledinský 1, A. Vetushka 1, J. Stuchlík 1, M. Müller 1, P. Pikna 1, M. Bouša 2, M. Kalbáč 2, O. Frank 2, A. Fejfar 1
Affiliations : 1 Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnická 10/112, 162 00 Prague, Czech Republic 2 J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 2155/3, 182 23 Prague, Czech Republic

Resume : Chemical vapour deposited (CVD) graphene has attracted significant interest as a promising transparent top electrode due to its unique optical and electrical properties applicable for example in photovoltaics (PV) [1]. In comparison with conventional transparent electrodes, graphene has higher transparency, namely in the infra-red region, and low sheet resistance (down to 10–30 Ω/square for high quality layers). Therefore, CVD graphene can replace metal layer in Schottky-barrier based solar cells [2]. In this paper, we describe local PV properties of metal-insulator-semiconductor (MIS) Schottky barrier solar cell composed of CVD graphene transferred on hydrogenated microcrystalline silicon (µc-Si:H) with native silicon oxide insulating layer. We prepared series of graphene/µc-Si:H samples with different thickness of SiO2 and studied its influence on PV properties. Surface morphology and local photoconductivity maps were probed by conductive atomic force microscopy (C-AFM). Moreover, PV quality was characterized by I-V curves obtained locally by C-AFM as well as by standard macroscopic I-V measurements. As the results gained by both techniques are consistent, we have demonstrated the C-AFM to a valuable tool how to measure PV properties at the nanoscale. [1] Li et al., Adv. Mater. 22 (2010) 2743–2748. [2] Song et al., Nano Lett. 15 (2015) 2104–2110. This research was supported by Czech Science Foundation project 14-15357S.

Authors : B. Pivac1, P. Dubček1, J. Dasović1, N. Radić1, S. Bernstorff2
Affiliations : 1 Ruđer Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia 2Elettra-Sincrotrone Trieste, SS 14, km 163.5, Basovizza (TS), Italy,

Resume : Germanium nanoparticles or quantum dots (QDs) embedded in transparent dielectric matrix have properties radically different from the bulk semiconductor and present a great potential for application in electronic and optoelectronic devices. Due to quantum confinement the optical bandgap of QDs based materials can be tuned by varying the nanoparticle size. These properties may be exploited for the fabrication of nanoscale electronic devices or advanced solar cells. In this work we explored the structural properties of QDs based superstructures for advanced solar cells. Magnetron cosputtering was used for deposition, and upon suitable thermal treatment a superstructure of QDs was formed. The structural properties were explored by GISAXS/GIWAXS analysis. Both the GISAXS and GIWAXS techniques were used to obtain the size of the grown objects and in addition, the Porod tail was analyzed in the GISAXS pattern in order to obtain information on the layer close to the Ge QD / matrix interface. The interface transition Ge QD / matrix will be discussed. We shall show that such a layer affects the time resolved PL properties of the Ge dots.

Authors : M.I. Sanchez 1, G. Coustillier 1, Y. Spiegel 2, T. Robert 2, F.Torregrosa 2, P. Delaporte 1, T. Sarnet 1
Affiliations : 1 Aix Marseille Université, CNRS, LP3 UMR 7341, 13288, Marseille, France 2 Ion Beam Services, ZI Peynier-Rousset, rue Gaston Imbert prolongée, 13790 Peynier, France.

Resume : The micro and nanostructured hyperdoped silicon, known as black silicon, is a highly absorbing surface with extended spectral sensitivity [1-2]. This material offers new opportunities and dramatically enhances the infrared sensitivity of silicon-based optoelectronic devices. However, and despite the potential increase in optical absorbance there is an important drawback caused by increase of the charge carrier recombination at the nanostructured surface [3]. This decrease in the lifetime of the carriers is mainly due to the defects created during the femtosecond laser irradiation of the material. A post-laser annealing (LA) of the nanostructured black silicon surface can reduce these defects [4, 5] by creating high crystallinity of the amorphous and polycrystalline surface induced in the black silicon fabrication [6]. Therefore, one important challenge is to increase the crystallinity of the black silicon structure, required to reduce these centres of recombination without reducing optical absorbance [7]. With this objective, this work shows a comparative study of Laser Annealing and simultaneous Laser Annealing and Plasma Immersion Ion Implantation (PIII) [8] process in order to solve the issue of surface recombination in black silicon solar cells, by providing good crystallinity and electrical performance. We demonstrate that either electrical or optical capabilities can be reached with LA and PIII. For this purpose several characterization measurements of the processed materials was carried out by means of Laser beam induced current (LBIC), four-point probe resistivity measurements, reflectivity and absorbance spectroscopy, Scanning electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDX) microanalysis.

Authors : F. Ehré(a), C. Dufour(a), L. Dumont(a), F. Gourbilleau(a), C. Frilay(a), X. Portier(a), J. Cardin(a), P. Marie(a), Wojciech M. Jadwisienczak(b), Andrea L. Richard(b), David C. Ingram(b) and C. Labbé(a)
Affiliations : (a) CIMAP CNRS/CEA/ENSICAEN/UNICAEN (b) School of Electrical Engineering and Computer Science, Ohio University, Stocker Center, Athens, OH 45701, USA

Resume : For now, commercial c-Si solar cells have a limited efficiency of about 25%; one of the reasons is the thermalization of high energy photogenerated carriers. Thus, a way for improving this efficiency is to introduce a frequency conversion layer in a cheap and compatible Si PV technology approach. The goal of our study consists in replacing the antireflective SiNx layer of commercial Si PV cell by a down converter layer based on a Ce3 -Yb3 co-doping and embedded in Bragg Mirrors. This system has been produced by reactive co-sputtering technique and their optical properties optimized through the deposition and annealing parameters. SiOxNy composition affects the 5d band of Ce3 ions which presents a wide and bright photoluminescence due to the 5d-4f transition. Excitation photoluminescence measurements show a wide excitation domain for the Ce3 ions ranging from 300nm to 400nm wavelength. Moreover, such an ion benefits from an efficient direct excitation of its 5d levels without any requirement of sensitization from the matrix. By introducing the Yb3 ions, we evidence an effective cooperative energy transfer with an internal quantum efficiency higher than 180 %. To improve the Ce3 -Yb3 coupling rate, Bragg mirrors on top and bottom of the doped SiOxNy layer have been designed. Simulations and experimental results are compared to define the optimized structure favoring the trapping of UV photons as well as the maximum of IR photons redirected to the solar cell.

Authors : A. Radu1, G.A. Nemnes1,2, S. Iftimie1, N. Vasile1, O. Toma1, L. Ion1, S. Antohe1,3
Affiliations : 1University of Bucharest, Faculty of Physics, Bucharest, Romania; 2Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering (IFIN-HH), Magurele, Romania; 3Academy of Romanian Scientists, Bucharest, Romania

Resume : AIIBVI thin film semiconductors based photovoltaic cells proved to be suitable candidates for both, terrestrial and space applications. Their wide bandgap, good chemical and mechanical stability and relatively low production price recommend these materials as important candidates for optoelectronic devices, especially for photovoltaic cells. Zinc sulfide (ZnS) thin films were deposited by rf-magnetron sputtering onto optical glass substrates. Deposition pressure was varied in the range 4×10-3 mbar – 1.6×10-2 mbar; other working parameters, like working power, substrate temperature and time deposition, were maintained constant. Optical absorption spectroscopy analysis showed a decrease of the bandgap energy of the deposited films with pressure increase. With transmittance higher than 70% for all deposited layers, ZnS thin films are suitable ”window” layers for AIIBVI semiconductors based photovoltaic cells. Structural and morphological features were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and charge carriers’ mobility was determined by Van der Pauw method in the 30 – 300K temperature range. Keywords: ZnS, rf-magnetron sputtering, photovoltaic cell Acknowledgements: This work was supported by Romanian Executive Unit for Financing Higher Education, Research and Innovation (UEFISCDI) under PN-II-PCCA program, grant no. 288/2014.

Authors : M. Nistor 1, F. Gherendi 1, L.Mihut 2, E. Millon 3, C. Cachoncinlle 3, C. Hebert 4,5, J. Perrière 4,5
Affiliations : 1 National Institute for Lasers, Plasma and Radiation Physics (NILPRP), L22 P.O. Box. MG-36, 077125 Bucharest-Magurele, Romania 2 National Institute of Materials Physics (NIMP), Atomistilor Str. 105 bis, P.O. Box MG-7, 077125 Magurele-Ilfov, Romania 3 GREMI, UMR 7344 CNRS-Université d’Orléans, 45067 Orléans Cedex 2, France 4 Sorbonne Universités, UPMC Univ Paris 06, UMR 7588, INSP, F-75005, Paris, France 5 CNRS, UMR 7588, INSP, F-75005, Paris, France

Resume : ZnO thin films are frequently used as transparent layer for photovoltaic applications but a recent approach is to obtain ZnO based solar spectrum converters by rare earth doping. Among these rare earth dopants, a particular interest has been shown on neodymium (Nd) with its near-infrared emission at about 900 nm which is compatible with silicon solar cells. In this work Nd doped ZnO films were grown by pulsed electron beam deposition on Si, glass and and c-cut single crystal substrates at different substrate temperatures and under oxygen gas (10-2 – 2 10-2 mbar). We demonstrate that a simple way to tune the physical properties of Nd doped ZnO thin films is given by a precise control of the growth conditions. The composition and structure of these films were correlated to their electrical (resistivity, mobility and carrier density) and optical properties (UV-VIS absorption and photoluminescence in the near infrared domain of the Nd3 ions). The results show that a slight difference in oxygen pressure has drastic effects on the film properties, leading from transparent conducting to photon down-shifting thin films.

Authors : M. Welna1, M. Baranowski1, W. M. Linhart1, R. Kudrawiec1, K. M. Yu 2,3, and W. Walukiewicz2
Affiliations : 1 Laboratory for Optical Spectroscopy of Nanostructures, Faculty of Fundamental Problems of Technology, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland 2 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 3 Department of Physics and Materials Science, City University of Hong Kong, Kowloon, Hong Kong

Resume : The energy band structure of highly mismatched alloys (HMAs) is strongly modified due to a band anticrossing (BAC) interaction of localized levels of isovalent dopants with the extended states of either conduction (CBAC) or valence (VBAC) band [PRL 82, 1221 (1999)]. This interaction leads to a formation of a narrow intermediate band in the semiconductor band gap. CBAC HMAs have been used to demonstrate an intermediate band solar cell concept [PRL 106, 028701 (2011)]. The key requirement for the IBSC operation is a presence of optical transitions between all bands. So far it has been only demonstrated for CBAC HMAs. Here we show a first observation of optical transitions between all VBAC split valence bands (VBs) and the conduction band of ZnO1-xSex HMA. We have studied optical properties of ZnO1-xSex alloys with up to 8% of Se. The ZnO1-xSex layers were grown on Al2O3 substrate by pulsed laser deposition technique [JAP 111, 113505 (2012)]. Using combination of optical techniques we clearly show that the observed 3 photoluminescence (PL) bands correspond to the transition from the conduction band to the lower valence subband and two spin-orbit split upper valence subbands. The results indicate relatively long lifetimes of photoexcited hole in the lower valence subband. The composition dependence of the PL peaks is explained by a 12x12 kp VBAC model describing the interaction between the VBs of ZnO and localized Se levels located 0.85 eV above the VB maximum of ZnO host matrix.

Authors : E. Zielony1, M. Morawski1, E. Płaczek-Popko1, A. Racino1, Z. Gumienny1, S. Chusnutdinow2 and G. Karczewski2
Affiliations : 1 Department of Quantum Technologies, Faculty of Fundamental Problems of Technology, Wroclaw University of Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wroclaw, Poland 2 Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46, 02-668 Warsaw, Poland

Resume : The n-i-p photovoltaic junctions based on CdTe/ZnTe has been studied for the presence of defects in their structure and their influence on the electrical properties of the diodes. The heterostructures were grown by MBE technique on the semi-insulating (100)-GaAs substrate. To study the origin of defects in the CdTe/ZnTe junctions the temperature photoluminescence (PL) measurements have been performed and deep level transient spectroscopy (DLTS) has been also applied. The analysis of PL experiments of the investigated samples revealed the presence of recombination centers in the absorber layer. Two types of optical transitions were observed in the PL spectra. Their activation energies of about 6 and 11 meV correspond to the free excitons and donor-acceptor pair radiative recombination, respectively [1]. The DLTS measurements confirmed the presence of recombination centers and several deep traps of activation energies equal to 0.22 eV, 0.45 eV and 0.78 eV. Their possible origin has been discussed. DLTS signal analysis let us assume that the deep traps are located in the absorber layer i-CdTe and at the i-CdTe/ZnTe interface [2]. Summarizing, the PL- and DLTS measurements allowed for characterization of defects present in the CdTe/ZnTe n-i-p junctions. It was found that these defects are responsible for the low efficiency of the studied solar cells. [1] J. Lee, et al., J. Appl. Phys. 78, 5669 (1995). [2] E. Zielony, et al., J. Appl. Phys. 115, 244501 (2014).

Authors : M. Müller, J. Červenka, J. Kočka, A. Fejfar
Affiliations : Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnická 10/112, 162 00 Prague, Czech Republic

Resume : Silicon nanowire arrays have recently become widely studied substrates for thin film solar cells, approaching 10% conversion efficiency [1]. Improving the efficiency further requires improved control and understanding of the metal catalyzed growth of the wires and a subsequent absorber layer. We have studied the growth of silicon nanowires under various deposition conditions (temperature, plasma power, precursor concentration) in PECVD. Layers of catalytic tin or indium metal nanoparticles on Corning glass with sputtered Al:ZnO thin films have been prepared by vacuum evaporation and a dewetting process at elevated temperatures. Silicon nanowires typically with a thicknesses of tens of nm and lengths of microns have grown after few minute silicon deposition; however, we show that under certain deposition conditions nanowires with a thickness below 10 nm can be grown. The nanowire diameter is strongly connected to the size of catalytic nanoparticles. Control of the nucleation by the various approaches (e.g. using the spin-on metal nanoparticles and the graphene coating of the substrate) will be discussed. Deposition conditions as well as the thickness of original metal film have a substantial effect on the nucleation and growth of nanowire arrays as revealed by SEM. These effects are discussed with respect to the improvement of the performance of solar cells based on these nanowires. [1] Misra, IEEE J. Photovoltaics. 5 (2015) Czech Science Foundation 16-12355S supported.

Authors : Željka Milanović1, Tihomir Betti2 and Branko Pivac3*
Affiliations : 1 Faculty of Engineering, University of Rijeka, Vukovarska 58, 51000 Rijeka, Croatia, 2 Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture, University of Split, Ruđera Boškovića b.b., 21000 Split, Croatia, 3 Ruđer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia,

Resume : The most commonly used method for timely obtaining percolation threshold value pc is calculating the number of occupied lattice sites p when the probability of percolation P(p) equals 0.5. This is, however, shown to be unreliable particularly when simulating thin films. In this research, using a simple cubic lattice and discrete percolation models, we show how initial setup parameters and processes implemented in computer simulations of disordered systems can have a significant influence on representation of system characteristics. The most reliable method for obtaining percolation threshold is from the maximum of average cluster size curve (excluding all existent percolation clusters). Percolation probability value equal to unity (for p>pc) shifts towards zero when decreasing one spatial dimension (thin film lattice), while percolation threshold remains approximately equal to the theoretical value when obtained from the average cluster size curve, excluding all existent percolating clusters. This is due to the multiplication of probabilities of each percolating cluster’s appearance, as thin lattice made by multiplying the bulk 3D lattice allows the existence of multiple percolating clusters even for p

Authors : Florian Oliva 1, Rokas Kondrotas 1, Maxim Guc 1, Paul Pistor 1, Xavier Alcobe 2, Edgardo Saucedo 1, Alejandro Pérez-Rodriguez 1,3, Victor Izquierdo-Roca 1
Affiliations : 1 Catalonia Institute for Energy Research (IREC), Jardins de les Dones de Negre 1, 08930 Sant Adrià del Besòs-Barcelona, Spain. 2 Centres Cientifics i Tecnologics CCiTUB, Universitat de Barcelona, C. Lluis Sole i Sabarís 1, 08028, Barcelona, Spain.CCiTUB. 3 IN2UB, Departament d’Electrònica, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, Spain

Resume : CuZnInSe3 compounds have been recently identified as promising material for PV application for their desirable optical and electrical properties,. Recently, a very promising device efficiency of 7.6% has been reported. Further development of these technologies strongly requires for a deeper understanding of the fundamental properties of these complex materials for the careful assessment of their crystalline structure, band gap, secondary phases, presence of defects and their dependence on the process parameters and layer composition. In this context, this work reports the detailed crystalline, optical and vibrational characterisation that has been performed by XRD, Raman scattering and PL on samples grown with different chemical composition ([Cu]/([Zn]+[In]) between 0.3 and 0.6). XRD shows narrow peaks with a pattern associated to a modified cubic Zinc-Blende structure. Raman spectra show a vibrational characteristic pattern similar to that from chalcopyrite CuInSe2 but with broader and distorted bands at 170–250 cm-1 region that are determined by overlapping of close frequency modes. The relative intensity of these peaks has a strong dependence on the chemical composition of the layers. Finally, temperature dependent PL measurements have also been performed to assess presence of defects in the layers, and the obtained data strongly suggest the existence of a direct bandgap that can be controlled in the 1.16eV to 1.32eV with chemical composition.

Authors : Kristin Bergum, Heine Nygard Riise, Edouard Monakhov, Bengt Gunnar Svensson
Affiliations : Department of physics, Centre for materials science and nanotechnology, University of Oslo, Norway

Resume : Cu2O is an interesting material for PV solar cell application mostly due to its direct band gap of 2.1 eV, making it a perfect companion to Si solar cells in a tandem structure. Combined, these can reach efficiencies of 41%. The highest efficiency solar cells (>5% of max 20%) utilizing Cu2O as the absorbing layer has been accomplished using thermal oxidation of Cu. Cu2O produced in such a manner is characterized by a high mobility close to single crystal values (~100 cm2/Vs). Although Cu2O is a low-cost material, for practical applications it would be desirable to use thin films instead of thick wafers. In this study we have investigated Cu2O films deposited by reactive magnetron sputtering. To achieve the best possible mobility in Cu2O films, many parameters have been optimized; oxygen partial pressure, deposition temperature, and power on target. However, the mobility remained fairly low, usually around 15-25 cm2/Vs. Solar cells with sputter-deposited Cu2O have so far shown a low degree of rectification and low efficiencies. It is possible that the low efficiency stem from a low mobility or poor crystallinity. Post-deposition rapid thermal processing (RTP) at moderate pressure of Cu2O samples shows a promising and remarkable increase in mobility, up to 53 cm2/Vs (950 °C, 3 min), while retaining a similar carrier concentration. RTP annealings may thus be a step towards higher efficiencies for Cu2O-based solar cells.

Authors : Hoora Sarajan, Simon Kirner, Bernd Stannowski, Bernd Rech, Rutger Schlatmann
Affiliations : Helmholtz-Zentrum Berlin

Resume : Amorphous/microcrystalline/crystalline silicon (a-Si:H/µc-Si:H/c-Si) triple junction solar cells can have an operating voltage large enough to directly split water, for which >1.6 V (depending on the catalysts) are needed. They may be an inexpensive alternative to high efficiency, high voltage multi junction solar cells based on scarce elements like III-V semiconductors. In addition to standard KOH pyramid texturing of the 140 µm thick n-type Cz wafers, we used a second acid-based polishing step to systematically smoothen the sharp V-shaped valleys. This way, we avoided defective regions in the 2 µm thick μc-Si:H middle and the 250 nm a-Si:H top cell. Quantitatively analyzing the surfaces by atomic force microscopy, we found that a reduction from 47° to 25° in the maximum of the surface angle distribution allowed an increase in open circuit voltage (Voc) of >130 mV and an increase in fill factor (FF) from 58% to >70%. By further optimizing the nanocrystalline silicon oxide (nc-SiOx:H) intermediate reflector layer placed between bottom and middle cell as well as the nc-SiOx:H top cell p-layer, we could increase solar to electricity conversion efficiency to 12.1% (short-circuit current density of 8.7 mA/cm², Voc = 1.95 V, FF = 70.4%), still limited by the middle cell current. The high current density at 1.6 V of >7.5 mA/cm² could allow high solar to hydrogen conversion efficiencies once proper catalysts are applied. We expect further rapid progress by thickness adjustments.

Authors : K. Bouras 1*, D. Aureau 2, G. Schmerber 3, H. Rinnert 4, G. Ferblantier 1, S.Colis 3, T.Fix 1, A. Etcheberry 2, A. Dinia 3 and A. Slaoui 1
Affiliations : 1 ICube, CNRS-Université de Strasbourg, UMR 7357, 23 rue du Loess, BP 20 CR, 67037 Strasbourg Cedex 2, France 2 ILV, Université de Versailles-St-Quentin en Yvelines, UMR 8180, 45 avenue des Etats Unis, 78000 Versailles, France 3 IPCMS, CNRS-Université de Strasbourg UMR 7504, 23 rue du Loess, BP 43, 67034 Strasbourg Cedex 2, France 4IJL, Université de Lorraine-CNRS, UMR 7198, Boulevard des Aiguillettes, 54506 Vandœuvre-l`es-Nancy, France

Resume : SnO2 as a standard TCO material have recently attracted special attention, thanks to the particular dual valency of tin and to the reversible transformation of the material that can occurs from p-type SnO to n-type SnO2 with excellent transport properties. Besides, SnO2 can be functionalized with Rare Earth elements (RE), which gives rise to new properties. In the field of solar cells, this class of materials can be used as conversion layer to adapt the incident solar spectrum to the solar cell absorption, reducing the losses due to carriers’ thermalization. In this work we present properties of SnO2 films co-doped with Nd (0.62 at.%) and Yb (1.3 at.%), elaborated by reactive magnetron sputtering. This co-doping process in SnO2 is reported for the first time. The films were elaborated at 100°C for the sake of compatibility with low temperature used for devices fabrication. The XRD analysis showed the phase transformation from amorphous SnO to crystalline SnO2 as a function of the oxygen gaz flow during elaboration. We gain better insight into the oxides proportions as well as the RE profile distribution through chemical analysis by XPS spectroscopy, which also showed that both REs (Nd and Yb) are well inserted in the structure and possess the 3+ valence state predicting that are optically active. Indeed, analysis by PL spectroscopy shows that under UV excitation of 325 nm, the SnO2:Nd:Yb films exhibit a wide and intense emission lines in the infrared region characteristic of Nd and Yb. Thanks to PLE measurements, an efficient energy transfer from the SnOx host matrix to each rare earth has been identified. In addition to that, second energy transfer was observed; Nd3+ ions are found to efficiently sensitize the Yb3+ ions. The films exhibit transparency laying between 75-90% with excellent transport properties, resistivities as low as 0,01 and mobilities as high as 29,6 cm2/V.s were measured. Such optical and electrical results are of potential interest to solar cells using Nd and Yb co-doped SnO2 films as TCO and photon down shifter.

Authors : P. Dubček1, B. Pivac1, J. Dasović1, V. Janicki1, S. Bernstorff2
Affiliations : 1Ruđer Bošković Institute, HR10000 Zagreb, Croatia 2 Elettra-Sincrotrone Trieste, SS 14 km 163.5, 34149 Basovizza (TS), Italy

Resume : Nanometer sized metallic particles, such as Cu, Ag and Au, possess specific optical properties due to the presence of a plasmon band which corresponds to a narrow absorption band in the visible spectral range. The plasmons lead to modification of the properties of the adjacent dielectric material in which the nanoparticles are included. Controlling the chemical environment of nanoparticles and tuning their size and shape, one can modify the macroscopic properties of the host matrix in a controllable manner. In our work, the focus was on Cu nanoparticles, synthesized in or on silica, thus forming a composite material. We produced the samples by high vacuum thermal evaporation of a single Cu layer on top of Si substrate. Some of the samples were also capped with a thin SiO2 layer. The samples were deposited at different substrate temperatures (up to 180°C), and annealed ex situ in high vacuum at temperatures up to 550°C. Nanoparticles development was studied by Grazing incidence small-angle X-ray scattering (GISAXS) and also by Atomic Force Microscopy and Scanning Electron Microscopy when capping layer was not applied. It is shown that higer annealing temperatures result in more spherical Cu nanoparticles, while lower deposition temperatures further enhance their oblateness. Finally, the plasmonic effect was monitored by UV-Vis reflectance spectroscopy, while the oxidation of nanoparticles was further studied by photoluminescence spectroscopy.

Authors : Wissem Dimassi
Affiliations : Laboratoire de Photovoltaïque, Centre de Recherches et des Technologies de l’Energie, Technopole de Borj-Cédria, BP 95, 2050 Hammam-Lif, Tunisia

Resume : A new process was developed to realise a multicrystalline silicon (mc-Si) solar cell. A O2/porous silicon-based gettering was applied to the mc-Si wafers. As a result an important enhancement of the minority carrier diffusion length L, the recombination velocity at grain boundaries Vr and the minority carrier life time was confirmed by The Light Beam Induced Current (LBIC) mapping. After gettering the oxidized porous silicon (ox-PS) was used as a mask. Micro-periodic fingers were opened on the porous silicon layer using a micro groove machining process to realise a highly doped regions n under the fingers and a local back surface field. The dark I–V curves show the decrease of the serial resistance and the enhancement shunt resistance. The LBIC mapping of the realized device, confirm the presence of a micro periodic local back surface field.

Authors : V. Smirnov, A. Lambertz, F. Urbain, F. Finger
Affiliations : IEK-5 Photovoltaik, Forschungszentrum Jülich, D-52425 Jülich, Germany

Resume : We present the development of high efficiency single and multi-junction solar cells, focusing on the stability against prolonged illumination. The degradation process, known as Staebler-Wronski effect, is considered as a major limiting factor for high efficiency cells and usually is associated with the stability of amorphous silicon (a-Si:H) absorber layers, while the microcrystalline silicon (μc-Si:H) absorber is generally more stable. We study the stability of single (a-Si:H) and multi-junction (a-Si:H and µc-Si:H based tandem, triple and quadruple junction) solar cells prepared by PECVD at deposition temperatures of 185°C or below. Solar cells were investigated by current-voltage (J-V) measurements under AM 1.5 illumination (intensity of 1000 W/m2, class A spectrum), quantum efficiency (QE) and reflectance measurements. Degradation of solar cell was performed at 55 °C with an intensity of 1000 W/m2 over a period of 1000 hours. High initial efficiencies were achieved for all types of solar cells: 12.4% in the case of a-Si:H single junction cell and above 13.5% for each type of multijunction cells. The degradation behaviour was evaluated with respect to the thickness and bandgap of the a-Si:H absorber layers. After 1000 hrs of illumination low degradation values of as little as 5 % from the initial value were found resulting in stabilized of degradation we achieved efficiencies of 11.8% in the case of tandem and triple solar cell, and of 12.1% in the case of quadruple cells.

Authors : J. Merigeon-1, Olfa Maalej-2,3, Brigitte Boulard-2, Mihaela Girtan-1
Affiliations : 1-Laboratoire LPHIA, LUNAM - Université d’Angers, 2 Bd. Lavoisier, 49045 Angers, France 2-Institut des Molécules et Matériaux du Mans, Université du Maine, Av. O. Messiaen, 72085 Le Mans, France 3-Laboratoire de Chimie Inorganique, Université de Sfax, Faculté des Sciences de Sfax, BP 1171, 3000 Sfax, Tunisia

Resume : Since the 50’s when the concept of the first semiconducting photovoltaic cell was practically proved, different materials and technologies were tested in order to increase the conversion efficiencies and to reduce the fabrication costs. Today world records conversion efficiencies for single junctions solar cells without concentrators are of 28.8% for thin film GaAs, of 25% for single crystal monocrystalline Si, 21.7% for CIGS thin films, 19.3% for perovskites cells, 13.4% for amorphous silicon thin films solar cells, 11.9% for dye –sensitized cells and of 11.1 % for organic solar cells. For the industrial development of different technologies many aspects should be taken into account: i) the efficiency, ii) the materials cost and iii) the life time of materials and solar energy devices. Due to the discrete band structure of semiconductors, only photons with energies equal or greater than the bandgap energy (Eg) will be absorbed and contribute to the electrical photovoltaic solar cell output. Photons having higher energies than Eg, even they are absorbed, their energies are underutilized due to the thermalization of charge carriers. In order to reduce these spectral losses and increase the energy conversion efficiency, many strategies were considered, such as: multi-junction cells (multiple semiconductors stacked cells), intermediate band semiconductors solar cells, up and down converters. Rare earth doped glass materials gives the opportunity to convert the incident photons wavelength and hence to increase or decrease their energies. In function of the nature of doping materials, the absorption of two low energy photons could contribute to the emission of one high energy photon (up-conversion), and also by the absorption of one high energy photon, one or two low energy photons could be generated (down-conversion). By converting the energies of photons which are not efficiently used, corresponding to the UV and respectively IR part of solar spectrum, the concept of “up and down conversion” is a possible way to increase the efficiencies of all classes of single junction solar cell. Pr3 /Yb3 co-doped ZBLA, Tm3 single-doped and Tm3 /Yb3 co-doped fluoride glasses based on ZLAG and ZBLA glasses showing a mechanism of down-conversion were tested as encapsulation glasses materials for monocrystalline silicon solar cells. The J-V characterizations were done under solar simulator irradiation. The influence of Yb3 and Tm3 concentration on the solar cells performances was investigated.

Authors : Rosaria A. Puglisi; Sebastiano Caccamo; Corrado Bongiorno; Salvatore Di Franco; Markus Italia; Giovanni Mannino; Silvia Scalese; Antonino La Magna
Affiliations : Consiglio Nazionale delle Ricerche, Istituto per la Microelettronica e Microsistemi (CNR-IMM) Strada Ottava 5, Zona Industriale, 95121 Catania, Italy.

Resume : Monolayer molecular doping (MD) has recently attracted much attention as an easy and cost-effective method to form p-n junctions in silicon [J. C. Ho et al., Nature Nanomater. 7, 62 (2008)]. It consists in the immersion of the sample in a chemical bath containing dopant precursors molecules diluted in a solvent. During this process the molecules deposit from the liquid all over the exposed surfaces, chemically bond to the target surface with a self-limiting process ruled by their steric properties and work as dopant source during successive thermal annealing. The technique allows the n- or p- type doping by the proper selection of the precursor source [Garozzo et al., MATER SCI ENG B 178 (2013) 686] and it has been successfully applied to structured surfaces [R. A. Puglisi et al., Phys. Stat. Sol. A 210 (2013) 1564]. Recently the method has been successfully demonstrated on Si nanowire array with density of 2×10^10 cm^-2, average length of 500 nm and diameters up to 70 nm [R. A. Puglisi et al., Sol. En. Mat. Sol. Cells 132 (2015) 118]. The doped nanostructures have been then integrated in complete solar cell devices exhibiting photovoltaic properties thus showing promising results for this easy and low cost method to be applied in the next generation of solar cells. We now present results of a study performed on MD applied to solar cells, where different contacts design and materials and passivation processes have been investigated. It is found that the optimized Si nanowire based solar cells present short circuit current as high as 9.3mA/cm2 under 1Sun of solar irradiation.

Authors : Suresh Kumar, Valdek Mikli, Tiit Varema, Mare Altosaar, Maarja Grossberg
Affiliations : Tallinn University of Technology, Institute of Materials Science Ehitajate tee 5, 19086, Tallinn, Estonia

Resume : Copper Zinc Tin Sulphide (CZTS) nano-powders were synthesised by solution based method in oleylamine at 215oC, 225oC and 235oC. The precursors used were copper pentanedionate, zinc acetate, tin (II) chloride and elemental sulphur. The influence of initial Cu/ (Zn +Sn) concentration ratio on the morphology, phase composition and elemental composition of nano-powders was studied. For every synthesis temperature the initial composition of precursors was varied by changing the Cu/ (Zn +Sn) concentration ratio (i.e. 0.83, 0.76, 0.62, 0.51 and 0.36). SEM analysis confirmed that the formation of nano-particles and/or colloidal nano-particles is depending on the initial composition. The CZTS nano-powders synthesised at 215oC, 225oC and 235oC with decreasing initial Cu/ (Zn + Sn) concentration ratio show increase in the size of colloidal nano-particles from 20 nm to 10 µm. EDS analysis revealed that the elemental composition of the formed nano-powders was stoichiometric CZTS with initial Cu/ (Zn +Sn) concentration ratio (i.e. 0.83 and 0.76) and for other concentrations the elemental composition of the formed nano-powders was close to the used initial composition. Raman analysis revealed that the phase composition of nano-powders depends on the used synthesis temperature and on the initial composition of precursor mixtures. By Raman analysis the nano-powders synthesised with the initial ratios of Cu/ (Zn + Sn) equal to 0.83 and 0.76 at 235oC show Raman peaks characteristic to CZTS.

Authors : Ankit Mittal (1,2), Gustav Ujvari (1), Marcus Rennhofer (1), Theodoros Dimopoulos (1), Martin Ursprung (3), Lukas Plessing (3), Viktor Schlosser (2)
Affiliations : (1) Austrian Institute of Technology, Giefinggasse 2, Vienna-1210, Austria (2) Department of Physics, University of Vienna, Boltzmanngasse 5, Wien-1090, Austria (3) Crystalsol GmbH, Simmeringer Hauptstrasse 24, 1110 Wien, Austria

Resume : Measurements of the photovoltaic (PV) activity of solar cells under low-light conditions and different wavelength-selective filters can supply useful information for the nature, the location and the activation of defects and recombination mechanisms inside the heterojunction and its interfaces. In this work we use this approach for the characterization of crystalsol monograin membrane kesterite (CZTS) solar cells. The temporal dependence of the open circuit voltage, short circuit current, fill factor and conversion efficiency, under low intensity of white, red, green and blue light is studied and related to carrier recombination processes in the bulk of the absorber and its interfaces with the CdS buffer and the electrodes. The low-light behaviour of the cells is discussed in relation to their PV performance under standard test conditions (1000 W/m2) and their external quantum efficiency. Reversible and irreversible contributions to the light-soaking effects are further analyzed. Finally, photoluminescence and electroluminescence imaging was used to elucidate the spatial homogeneity and quality of the monograin cells.

Authors : J. Lauwaert, H. Vrielinck, S. Khelifi
Affiliations : 1 Department of Electronics and Information Systems (ELIS), Ghent University, St.-Pietersnieuwstraat 41, B-9000 Gent, Belgium 2 Department of Solid State Science, Ghent University, Krijgslaan 281-S1, B-9000 Gent, Belgium

Resume : The kinetic compensation effect or Meyer-Neldel exists as a fundamental property of strongly related processes. It is therefore often used in the electric characterization of semiconductors to evaluate if detected signals have a similar origin. In the past this has for example led to a criterion to evaluate if an anomalous signal capacitance spectroscopy signal can be assigned to the famous N1-signal in CIGS solar cells. In this work we calculate the probability to detect a thermally activated signal in admittance and deep level transient spectroscopy as a function of the activation energy and the pre-exponential factor. Based on these calculations we compare probability of finding a kinetic compensation effect in the spectra with the ideal situation where all signals have the same probability of being detected. We conclude that great care should be taken when using the kinetic compensation effect as an argument that signals have a similar (the same) origin.

Authors : Alessandro Bellucci,1, Paolo Calvani,1, Marco Girolami,1, Stefano Orlando,2, Riccardo Polini,3, Veronica Valentini,1, and Daniele Maria Trucchi,1*
Affiliations : 1 Istituto di Struttura della Materia (ISM) - National Research Council (CNR), Unit of Montelibretti (RM) 2 Istituto di Struttura della Materia (ISM) - National Research Council (CNR), Unit of Tito Scalo (PZ) 3 Dipartimento di Scienze e Tecnologie Chimiche - Università di Roma “Tor Vergata”

Resume : High-temperature solar cells are possible with Photon-enhanced Thermionic Emission (PETE) devices, which represent a novel and very attractive concept for the exploitation of solar radiation, especially if concentrated, characterized by a promisingly high conversion efficiency. PETE converters rely on the concept that engineered semiconductor structures can provide a hot-electron emission, induced by photons with sufficient energy to produce charge couples, combined to a thermionic emission, sustained by the high temperatures induced by every thermalization process. Surface nanotexturing combined to surface-hydrogenation, aimed at achieving negative electron affinity conditions and a work function as low as 1.7 eV with an emitting-layer nitrogen-doping, are here proposed as a radically new and potentially efficient PETE cathode completely based on chemical-vapour-deposited (CVD) diamond, able to ensure an efficient thermionic emission at temperatures up to 780 °C. CVD diamond is transparent to solar radiation due to its wide bandgap, consequently advanced and novel techniques are needed for processing diamond to become an efficient sunlight absorbing material (i.e. black diamond). Surface texturing by fs-laser, boron-implantation, buried and distributed graphitic structures and other technological steps allow for the fabrication of an innovative defect engineered diamond cathode to be efficiently exploited for the conversion of concentrated solar radiation. A diamond-based anode with an even lower work-function can be combined to the efficient black diamond cathode.

Authors : Andreia Araújo,* Manuel J. Mendes, Tiago Mateus, António Vicente, Daniela Nunes, Tomas Calmeiro, Elvira Fortunato, Hugo Águas* and Rodrigo Martins*
Affiliations : i3N/CENIMAT, Department of Materials Science, Faculty of Science and Technology, Universidade NOVA de Lisboa and CEMOP/UNINOVA, Campus de Caparica, 2829-516 Caparica, Portugal

Resume : There has been an increased interest in the scattering properties of plasmonic metal nanoparticles to enhance light trapping in opto-electronic devices, such as thin film solar cells. In most cases the nanoparticles are self-assembled over a transparent conductive oxide (TCO) layer of the cells structure. However, until now, little is known about the influence of the substrate (typically glass + TCO) properties on the morphology of the nanoparticles formed. As such, this work presents a complete morphological and optical study of a series of silver nanoparticle structures fabricated on distinct oxides relevant for solar cells application. The results of such comparative study reveal that the TCO conductivity and its surface roughness are key factors that control the morphology of the nanostructures. Therefore, the tuning of such properties allowed the production of remarkably uniform silver nanoparticles with the required sizes (100-300 nm) for efficient light scattering. In addition, a novel and fast method of fabricating highly reproducible plasmonic surfaces is explored, employing a rapid thermal annealing process.

Authors : Negar Gheshlaghi (a); Hadi S. Pisheh (a); M. Rezaul Karim (b); Derya Malkoç (a); Hilmi Ünlü (a,b)
Affiliations : (a) Nanscience and Nanoengineering Programme, Institute of Science and Technology İstanbul Technical University, Maslak Istanbul 34469 TURKEY (b) Department of Physics, Faculty of Science and Letters İstanbul Technical University, Maslak Istanbul 34469 TURKEY

Resume : Semiconductor nanocrystals (known as quantum dots (QDs)) have been the subject of great scientific and technological interest due to their potential optical applications that include photovoltaics, light emitting diodes (LEDs) and lasers. ZnSe and CdSe based quantum dots (QD) are semiconductor nanocrystals that possess unique optical properties and they are the potential candidate for next generation LEDs and photovoltaic devices. Their emission color can be tuned from the visible throughout the infrared spectrum. In this work we report a synthetic route to prepare type-I and type-II heterostructure ZnSe/Zn(Cd)S and CdSe/Zn(Cd)S colloidal core/shell spherical quantum dots, respetively. The synthesized ZnSe/Zn(Cd)S and CdSe/Zn(Cd)S heterostructure core/shell nanocrystals were characterized by using the x-ray diffraction (XRD) for structural properties and UV absorption and fluorescence techniques for optical properties, respectively. The effects of lattice mismatch induced interface strain on the first exciton energy, conduction and valence band energies and diameter of the ZnSe/Zn(Cd)S spherical core/shell quantum dots were calculated by using the effective mass approximation and nearest neigbour sp3s* tight binding theory. It is shown that the interface strain decreases the core diameter in CdSe/ZnS and ZnSe/ZnS type I heterostructures and increases it in the case of the ZnSe/CdS type II heterostructures.

Authors : Thomas Dittrich
Affiliations : Helmholtz - Zentrum Berlin für Materialien und Energie GmbH

Resume : Knowledge about the specific role of electronic transitions in photo-active materials and their interfaces is of great interest for the further development of solar cells based on thin films and nanocomposites. Transient surface photovoltage (SPV) spectroscopy is proposed as a method allowing the time and spectrally resolved study of electronic states involved in spatial charge separation. In this method, SPV transients are measured at numerous wavelengths and the SPV signals at fixed times are converted into spectra. Examples will be shown for different photo-active materials and their combinations. The separation between shallow and deep electronic states in relation to the relaxation over a space charge region or a very thin defect layer will be demonstrated.

Authors : Steffen Fengler, Thomas Dittrich
Affiliations : Helmholtz - Zentrum Berlin für Materialien und Energie GmbH

Resume : Separation in space and localization of photogenerated charge carriers can be investigated by surface photovoltage (SPV) techniques. The in-phase and phase-shifted by 90° signals or, in equivalence, the amplitide and phase angle of modulated SPV spectra contain information about the dynamic behavior of processes of charge separation and relaxation of a given sample. However, a detailed analysis of modulated SPV signals is usually not straight forward since localization of different charge carriers can last over different orders of magnitude in time. A model has been developed for the simulation of modulated SPV signals. The model is based on a random walk of a charge carrier across localized states and its interaction with delocalized and recombination states. The correlation between the SPV amplitude and the phase angle is discussed and compared with examples. The method will allow a deeper analysis of localized states at charge-selective contacts.

Authors : A. F. Zatsepin (1), Yu. A. Kuznetsova (1), L. Spallino (1, 2), V. A. Pustovarov (1), V. N. Rychkov (1)
Affiliations : (1) Institute of Physics and Technology, Ural Federal University, Mira Street 19, Ekaterinburg 620002, Russia (2) Dipartimento di Fisica e Chimica, Università di Palermo, Via Archirafi 36, I 0123 Palermo, Italy

Resume : Gadolinium oxide is a promising material for the conversion of solar radiation since it provides the possibility of doping TR3+ ions in a wide range of concentrations and creating a donor -acceptor pairs for down- and up-conversion processes. The efficiency of these processes depends on a lot of factors particularly on the structural- phase composition, dispersion, purity of host lattice. The aim of this work is to determine the role of the Gd2O3 matrix intrinsic and impurity-related defects in the excitation energy transport mechanisms. To this purpose we carried out a detailed investigation of micro- and nanostructured Gd2O3, both nominally pure and doped with TR3+ ions by using luminescence and thermo-activation spectroscopy methods. Both intrinsic lattice defects and impurity-related defects were detected and the kinetic parameters of the charge trapping centers were determined. These results allowed us to discuss the nature of the defects states and the effective mechanism of energy transfer processes from host Gd3+-ions to impurity TR3+-ions. The contribution of band charge carriers in energy transfer processes are discussed.

Authors : A. Simashkevich*, L.Bruc*, N. Curmei*, D. Serban*, A. Thogersen**, A. Ulyashin**
Affiliations : * Institute of Applied Physics, Kishinev, Moldova **SINTEF Materials and Chemistry, Oslo, Norway

Resume : The goal of this work is to demonstrate that spray pyrolysis technique for deposition of ITO layers can be effectively used for the cost effective processing of ITO/n-type Si based solar cells. This approach does not require formation of an emitter. However, special treatments of n-type Si substrates, to prepare a buffer layer between ITO and Si are still required. Two approaches for the formation of such buffer layers have been considered: (i) chemical etching, which results in a formation of a thin Si porous layer and (ii) low- temperature (~400 ∘C) anneals, which result in a formation of an thin (~1 nm) SiOx layer. High resolution electron microscopy has been used for the analysis of individual ITO layers as well as ITO/Si interfaces. It is established that formation of an ultra-thin SiOx layer at the ITO/Si interface is the most promising route to fabricate heterojunction ITO/Si solar cells with the reasonable (above 14%) efficiencies at a low-cost. Further steps for optimization and improvement of the low-cost processing routes for ITO/Si solar cells will be discussed.

Authors : M. Bouras, A. Hocini
Affiliations : Laboratoire d’Analyse des Signaux et Systèmes, Department of Electronics, University of M’sila BP.166, Route Ichebilia, M’sila, 28000 Algeria

Resume : structured active or absorbing layers of solar cells, including photonic crystals and wire arrays, have been increasingly explored as potential options to enhance performance of thin film solar cells because of their unique ability to control light, using the Rigorous Coupled Wave Analysis (RCWA). The designs are tested in four relevant materials: amorphous silicon (a-Si), crystalline silicon (Si), gallium arsenide (GaAs) and indium phosphide (InP). The parameters for photonic crystals are optimized through computer simulations to obtain the maximum absorption and path length enhancement. We investigated the performance of the considered structure and determined the geometrical parameters that allow a better absorption.

Authors : Özge Bayraklı^1-2, Hasan Huseyin GULLU^1-2, Emre Coskun^3 and Mehmet PARLAK^1-2
Affiliations : 1. Department of Physics, Middle East Technical University (METU), Ankara 06800, Turkey 2. Center for Solar Energy Research and Applications (GÜNAM), METU, Ankara 06800, Turkey 3. Department of Physics, Çanakkale Onsekiz Mart University, Çanakkale 17100, Turkey

Resume : Zinc indium selenide (ZnIn2Se4) thin films have wide applications in solar cells and optoelectronic devices [1,2]. ZnIn2Se4 is n-type ternary chalcogenide semiconductor of type AIBIIXIV, where A=Zn, Cd, or Hg, B=In or Ga, and X=Se, S, Te [3–14]. In and Ga are rare elements and they can be replaced by earth abundant elements such as Zn or Sn. In this work, in the interest of window layer for possible photovoltaic applications with chalcopyrite and kesterite structures, the device properties for the Zn-Sn-Se thin films were studied. ZnSnSe2 (ZTSe) thin films were deposited by using single crystalline powder of sintered ZnSnSe2. The deposition process was carried out by means of e-beam evaporation on the p-Si substrate and keeping them at the substrate temperature of 200°C. Current-voltage (I-V) measurements and frequency dependent capacitance-voltage (C-V) measurements were carried out to investigate its electrical characteristics. Device parameters such as diode ideality factor, barrier height, series and shunt resistances were obtained and the possible conduction mechanisms were analyzed. The series and shunt resistances were calculated as 3.98x10^2 and 2.71x10^6 Ω respectively. The diode ideality factor evaluated approximately as 2.7 and the barrier height found as 0.77 eV. From C-V measurements, the built-in potential and the acceptor- donor level densities were determined. [1] F.J. Gracia, M.S. Tomar, Thin Solid Films 69 (1980) 137. [7] J. Fillpowicz, N. Romeo, L. Tarricone, Solid State Commun. 38(1980) 619. [3] L. Gastaldi, M.G. Simcon, S. Vitivoli, Solid State Commun. 55 [4] J.A. Buan, R. Nitsche, M. Lichtensteiger, Physica 27 (1961) 448.985) 605.

Authors : Deniz Turkay1,*, Wei-Chun Hsu2, Matthew Branham2, Gang Chen2, Selçuk Yerci1,2,3
Affiliations : 1Department of Electrical and Electronics Engineering, Middle East Technical University, Ankara, 06800, Turkey 2 The Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA 3 Micro and Nanotechnology Programme, Middle East Technical University, Ankara, 06800, Turkey

Resume : The solar industry has been dominated by crystalline silicon (c-Si) solar cells despite the relatively high cost of silicon (~40% of the total module cost). One possible path to decrease the cost of c-Si solar cells is to reduce the thickness of silicon to a few tens of micrometers. For such thin films, superior light-trapping schemes are required to overcome the small absorption coefficient of silicon. Recently, various light-trapping structures operating in the wave optics regime have been introduced to boost the absorption in thin-film c-Si. However, a multiphysics optimization considering both optical absorption and carrier collection efficiencies has not been previously studied in detail. Here, we describe simulations we performed to show the trade-offs when designing advanced light-trapping structures for thin silicon films. Our simulation is capable of quantifying losses due to Shockley-Read-Hall at the bulk and surface, and Auger bulk recombination, as well as optical and contact losses. We found that efficiencies above 20% can be achieved using thin-film (<10 m) c-Si solar cells. Additionally, we simulated thin-film c-Si solar cells with an interdigitated back contact scheme, and demonstrated a super-linear dependence between back contact separation and minority carrier lifetime. Finally, we calculated the optimum height to period ratio of light-trapping structures to be around 0.7 for a fixed period of 700nm that can be obtained in silicon using well-known potassium hydroxide anisotropic etching. The effect of surface recombination was investigated in detail both for the front and back surfaces for this optimum dimensions. It was observed that there was up to 1% efficiency difference between cells which has surface passivated at 5 cm/s and 100 cm/s surface recombination velocity, and up to 3% difference between 5cm/s and 1000 cm/s. These multiphysics simulation results can provide design insights for flexible and high efficiency thin silicon solar cells.

Authors : Intu Sharma1*, Bodh Raj Mehta1*
Affiliations : 1Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi, 110016, India

Resume : 2D Molybdenum disulfide layers are of considerable research interest for a variety of optoelectronic applications due to the possibility of tuning the optical and electrical properties by controlling the number of MoS2 layers. Bulk MoS2, a p type material, shows an indirect band gap of 1.2 eV and when prepared in monolayer form it exhibit n type conductivity and direct band gap of 1.8 eV. ZnS is an n type wide band gap material and is used in a number of optoelectronic applications. In this study, heterojuctions of 2D MoS2 layers and ZnS thin films are prepared by combining radio frequency magnetron sputtering technique and sulfurization process. Depositions of ZnS and Mo films have been carried out sequentially followed by sulfurization of Mo coated ZnS thin films in a 2 zone tube furnace. Mo deposition time and amount of sulphur are varied to obtain bulk, few and monolayer of MoS2 on ZnS thin films. Structural, optical and surface photo voltage studies are performed by using x-ray diffraction (XRD), Raman, spectroscopic ellipsometry (SE), photoluminescence (PL) and Kelvin probe force microscopy (KPFM) techniques. XRD, Raman, SE and PL techniques show signatures of both ZnS and MoS2 (bulk, few and monolayer), confirming the formation of heterojunctions. Surface potentials studied under dark and light conditions using KPFM show charge transfer at the interfacial regions under illumination. Surface photo voltage in p MoS2/ n ZnS was observed to be higher than the n MoS2/ n ZnS hetero-interface.

Start atSubject View AllNum.Add
Tandem Structures : J.J. Schermer
Authors : Stephanie Essig1,3, Myles A. Steiner1, Christophe Allebé2, Jérémie Werner3, John F. Geisz1, Bertrand Paviet-Salomon2, Scott Ward1, Antoine Descoeudres2, Vincenzo LaSalvia1, Loris Barraud2, Arnaud Walter3, Nicolas Badel2, Jonathan Champliaud2, Stefaan De Wolf3,Antonin Faes2, Jacques Levrat2, Adele Tamboli1, Bjoern Niesen2,3, Matthieu Despeisse2,Christophe Ballif2,3, Paul Stradins1, David L. Young1
Affiliations : 1National Renewable Energy Laboratory (NREL), Golden, Colorado, USA 2Swiss Center for Electronics and Microtechnology (CSEM), Neuchâtel, Switzerland 3École Polytechnique Fédérale de Lausanne (EPFL), PV-Lab, Neuchâtel, Switzerland

Resume : The conversion efficiency of Si single-junction solar cells is fundamentally limited to <30%. Adding a wide-bandgap top cell with Eg=1.6-1.9eV to the Si cell reduces the themalization losses in the short wavelength region and enables theoretical efficiencies up to 38%. Suitable top cell materials are III-V semiconductors and organic-inorganic metal halide perovskites. Both material systems allow a wide range of bandgap energies; however, their application in photovoltaic devices is at different levels of evolution. Solar cells made of III-V semiconductors are wellestablished for the power generation of satellites and they have been successfully applied in terrestrial concentrator system. In contrast to these relatively expensive devices, perovskite solar cells are a promising low-cost approach, but have only been fabricated on a small research scale and their long-term stability is still under investigation. In our talk, we will discuss the development of Si-based tandem solar cells with both perovskite and III-V semiconductor top cells. A new record one-sun tandem cell efficiency of 29.8% was achieved with a mechanically stacked GaInP/Si device. The rear-heterojunction GaInP top cell and Si heterojunction bottom cells were fabricated independently at NREL and CSEM, respectively, and combined using an optically transparent, electrically insulating epoxy. The 4-terminal tandem cell device structure has been optimized by simulations, and the effect of luminescent coupling between the subcells has been investigated both experimentally and theoretically. PV-Lab’s monolithic perovskite/Si tandem cells will also be discussed; we have recently achieved an efficiency of 21.2% under one-sun, which will be further optimized.

Authors : M. Da Silva, C. Cornet, A. Létoublon, C. Levallois, A. Rolland, J. Even, L. Pédesseau, Y. Ping Wang, S. Wang, A. Le Corre, S. Boyer-Richard, P. Rale, L. Lombez, J.-F. Guillemoles, F. Mandorlo, M. Lemiti, A. Ponchet, O. Durand
Affiliations : UMR FOTON, CNRS, INSA Rennes, Université de Rennes 1, F35708, Rennes, France; Institut de Recherche et Développement sur l'Energie Photovoltaïque (IRDEP), UMR 7174 - CNRS-EDF-ENSCP, EDF R&D - Chatou, France; NextPV, LIA CNRS-RCAST/U. Tokyo-U. Bordeaux - Tokyo, Japan; University of Lyon, Lyon Institute of Nanotechnology (INL) UMR CNRS 5270, INSA de Lyon - Villeurbanne, France; CEMES-CNRS, Université de Toulouse, UPS, 29 rue Jeanne Marvig, BP 94347 Toulouse Cedex 04, France

Resume : Nowadays, the best solar conversion efficiencies have been reached thanks to multijunction solar cells consisting of a stacking of III-V semiconductor single junctions on GaAs or Ge. While displaying record efficiencies, these solar cells suffer from the cost of such substrates. Therefore, our strategy is to develop a tandem cell on Si, in order to benefit from both the low cost and technological maturity of Si cells. Indeed, it has been shown that a tandem cell consisting of a 1.7 eV bandgap material on a 1.1 eV Si cell would reach efficiencies up to 37%1. To this aim, we use GaP, grown by MBE, which is quasi lattice-matched with Si. In addition to reaching a perfect lattice matching with Si and improving its optical properties, As and N incorporation in GaP, leading to a GaAsPN absorber,2,3 reduces the bandgap from 2.3 eV to the required 1.7 eV. We have obtained first stage results on GaP/GaAsPN/GaP top pin cells on both GaP and Si substrates, displaying Voc of 0.9 V, and 0.7 V respectively, and Jsc of 3.77 mA/cm² and 3.69 mA/cm² resp. On GaP, a 2.3% conversion efficiency has been obtained. Moreover, a Si(n)/Si(p) tunnel junction, suitable for electrical connexion between the top and bottom cells, has also been obtained. Finally, first-stage development of complete GaAsPN/Si tandem cells is shown. 1Geisz, J. F., and D. J. Friedman, Semicond. Sci. Tech. 17.8 (2002): 769. 2S. Ilahi et al, Sol. Energ. Mat. Sol. C 141 (2015) 3S. Almosni et al, Sol. Energ. Mat. Sol. C 147 (2016)

Authors : Oliver Supplie (1,2), Matthias M. May (1,2,3), Agnieszka Paszuk (1), Andreas Nägelein (1), Peter Kleinschmidt (1), Sebastian Brückner (1,2), and Thomas Hannappel (1,2)
Affiliations : (1) TU Ilmenau, Institute for Physics, Photovoltaics group, Ilmenau, Germany (2) Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Institute for Solar Fuels, Berlin, Germany (3) current address: University of Cambridge, Chemistry Department, Lensfield Rd, Cambridge CB2 1EW, United Kingdom

Resume : III-V/Si(100) tandem absorber structures are promising for high-efficiency PV and direct solar water splitting [1]. Metalorganic vapor phase epitaxy (MOVPE) of such structures commonly involves arsenic, either supplied directly via precursors (e.g. TBAs) or in form of residuals. Here, we study the influence of As on Si(100) surfaces and GaP/Si(100) quasisubstrates in situ during MOVPE [2]. Annealing of Si(100) in TBAs and background As results in an As-modified surface with a characteristic in situ reflection anisotropy spectroscopy (RAS) signal. We show that its spectral features emerge at different stages of a two-step annealing process. LEED patterns of the final surface show a preferential A-type, (1x2) reconstructed surface with dimer rows in parallel to the step edges. These are also clearly visible in STM images. XPS evidences the presence of As at the surface, but also atomic exchange across the interface. After subsequent pulsed GaP nucleation and pseudomorphic GaP heteroepitaxy, we achieve atomically well-ordered GaP/Si(100) quasisubstrate surfaces, which are free of antiphase disorder. The sublattice orientation of the GaP film is inverted compared to GaP grown on H-terminated Si [3]. The atomic structure of the heterointerface is more complex than in the abrupt Si-P case [3] for As-free systems. Ref's: [1] M.M. May et al., Nat. Commun. 6, 8256 (2015). [2] O. Supplie et al., APL Mater. 3, 126110 (2015). [3] O. Supplie et al., J. Phys. Chem. Lett. 6, 464 (2015).

Authors : Vladimir Neplokh, Ahmed Ali, François H. Julien, Martin Foldyna, Ivan Mukhin, George Cirlin, Jean-Christophe Harmand, Noëlle Gogneau, Maria Tchernycheva
Affiliations : Vladimir Neplokh: Institut d’Electronique Fondamentale, UMR CNRS 8622, University Paris Sud 11, Orsay, 91405, France; Ahmed Ali: Institut d’Electronique Fondamentale, UMR CNRS 8622, University Paris Sud 11, Orsay, 91405, France; François H. Julien: Institut d’Electronique Fondamentale, UMR CNRS 8622, University Paris Sud 11, Orsay, 91405, France; Martin Foldyna: Laboratoire de Physique des Interfaces et Couches Minces (LPICM), CNRS, Université Paris Saclay, 91128 Palaiseau, France; Ivan Mukhin: ITMO University, St. Petersburg, 197101, Russia, St. Petersburg Academic University, Khlopina 8/3 A, St. Petersburg, 194021, Russia; George Cirlin: ITMO University, St. Petersburg, 197101, Russia, St. Petersburg Academic University, Khlopina 8/3 A, St. Petersburg, 194021, Russia, Ioffe Institute, Polytechnicheskaya 26, St. Petersburg, 194021, Russia; Jean-Christophe Harmand: Laboratoire de Photonique et de Nanostructures Route de Nozay, 91460 Marcoussis; Noëlle Gogneau: Laboratoire de Photonique et de Nanostructures Route de Nozay, 91460 Marcoussis; Maria Tchernycheva: Institut d’Electronique Fondamentale, UMR CNRS 8622, University Paris Sud 11, Orsay, 91405, France.

Resume : We report on the electron beam induced current (EBIC) investigation of GaN nanowires grown on n-type Si (111) substrates. The objective of this study is to acquire information about the modifications of the substrate properties induced by the wire growth in view of the future development of nitride-on-silicon tandem photovoltaic devices. We show that the growth procedure, using a deposition of an ultra-thin AlN film prior to the nanowire growth step, leads to the formation of a p-n junction in the Si substrate with a high surface conductivity. The induced p-n junction exhibits a photoresponse over the spectral range from 360 to 1100 nm. The properties of the induced p-n junction are investigated in cross-section and top-view configurations with EBIC microscopy. For a localized contact of the GaN nanowires , the induced current collection range in Si extends over a few millimeters . The treatment of the surface using reactive ion etching with a CHF3 plasma leads to the inhibition of the surface conductivity and to the appearance of an S-shape in the current-voltage characteristics under illumination. Nevertheless, the conversion efficiency of the plasma-treated sample under AM1.5G solar spectrum is estimated to be in the 2.1-2.7% range.

Authors : F. Gibelli, L. Lombez, J.F. Guillemoles
Affiliations : IRDEP UMR 7174 CNRS-EDF-ENSCP, 6 quai Watier, 78400 CHATOU (France) LIA NextPV, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan; IRDEP UMR 7174 CNRS-EDF-ENSCP, 6 quai Watier, 78400 CHATOU (France), LIA NextPV, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan, IPVF, 8 rue de la Renaissance, 92160 Antony FRANCE; IRDEP UMR 7174 CNRS-EDF-ENSCP, 6 quai Watier, 78400 CHATOU (France) LIA NextPV, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan IPVF, 8 rue de la Renaissance, 92160 Antony FRANCE;

Resume : The law governing the radiation emitted by a blackbody has been written by Planck. Further developments rooting on this law yielded a somewhat generalized equation for the light emitted by semiconductors where electrons and holes were characterized by Fermi-Dirac distributions at the same temperature but different quasi-Fermi levels. Here we further generalize a non-equilibrium generalized Planck's law accounting for different electron and hole temperatures, different from each other and different from the lattice temperature of the material. With an analytical expression of the absorption coefficient this non-equilibrium generalized Planck's law has been successfully used for fitting photoluminescence spectra recorded at different incident photon fluxes for an InGaAsP multi quantum well structure. Whereas the two carriers are heated during the experiment, electrons with lower effective mass are hotter than holes. The analysis of electrochemical potential variations shows a clear diminution for both carriers at high incident photon flux, which is more important for the holes. This work shows for the first time the relationship between individual carrier temperatures and the emission temperature usually measured with the classical expression of the generalized Planck's law. Moreover the individual absolute electrochemical potentials can also be experimentally extracted. We believe that these results open new perspective for hot carrier solar cell research. More generally, this work sheds light on new approaches for both photovoltaic and thermoelectric research. Planck, Vorlesungen über die Theorie der Wärmestrahlung, 1906 Lasher & Stern, Phys Rev 133, 1964; Würfel J. Phys Chem C (15) 1982 J. Rodiere et al., Appl. Phys Lett. 106, 183901 (2015 F. Gibelli et al. Phys. Rev. Applied, 5 (2), 2016 F. Gibelli et al., J. Phys. Cond. Mat, Submitted

Light Management II : Stephanie Essig
Authors : J.J. Schermer, G.J. Bauhuis, P. Mulder
Affiliations : Radboud University, Institute for Molecules and Materials, Heyendaalseweg 135, 6524 AJ Nijmegen, the Netherlands

Resume : Epitaxial lift-off is used to create thin-film III-V solar cells without sacrificing the GaAs wafer. It is based on selective etching of an AlAs release layer between the wafer and the cell structure using an HF solution. The wafer can be reused thereby reducing the cost of the cells. The thin-film cell can be transferred to any new carrier, e.g. glass, plastic, silicon or metal foil and offer new cell applications based on their flexibility, low weight and possibility to deposit the cell structure in reverse order. Moreover, thin-film cells with a back-contact that also acts as a mirror yield efficiencies surpassing that of the regular wafer based III-V cells because of an increased photon recycling. In the presentation the influence of junction depth in III-V cell structures will be discussed. Typical III-V cells employ a shallow junction design but our study indicates that for GaAs as well as InGaP cells, a deep junction close to the back of the cell structure performs better than a shallow junction. At the maximum power point the deep junction cells operate mainly in the radiative recombination regime, while in the shallow junction cells non-radiative recombination is dominant. The steeper slope of the IV curve boosts the fill-factor by 3-4%, which is thereby the most improved cell parameter. In order to minimize collection losses in the upper part of the cell, the optimal thickness of the GaAs deep junction cell is only two-thirds of a shallow junction cell. The associated lower cell current is more than compensated by the higher fill-factor and open circuit voltage yielding efficiencies up to 26.5% for a GaAs cell on its native substrate. In the presentation the implications of the deep junction cell design for thin-film cell performance will be discussed.

Authors : F.-J. Haug
Affiliations : Ecole Polytechnique Fédérale de Lausanne (EPFL), PV-Lab

Resume : With an overwhelming market share of more than 90% in the sales of solar modules, crystalline silicon seems to be the ideal photovoltaic material. However, its success does not exempt silicon technology from the urgent need for further improvements. High efficiency devices like the PERL cell of UNSW or the HIT cell of Panasonic achieved a remarkable level of maturity, but their fabrication is too complicated for mass production on GW scale. Yet, they define ways for the improvement of current mainstream technology. One of them is further thinning of the wafers for reduced material consumption and, assuming excellent surface passivation, for improved open circuit voltage. The optics of the device must be developed accordingly in order to ensure a full absorption of the incident light in continuously reducing wafer volumes. Standard texturing methods are based on anisotropic etching of facets on a length scale of tens of micrometres which are suitable described by tracing of individual rays. In thinner cell designs the feature size will shrink accordingly, pronouncing the effect of scattering centres over refraction at planes.

Authors : D. Eisenhauer, K. Jäger, D. Chen, B. Rech, C. Becker
Affiliations : Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Kekuléstr. 5, 12489 Berlin

Resume : Liquid-phase crystallization (LPC) of silicon is an emerging technology for high quality thin-film silicon solar cells on glass substrates. Using this bottom-up approach avoids handling issues associated with thin wafer technology. With 10 µm thin silicon layers with wafer equivalent morphologies, open-circuit voltages well above 600 mV could be achieved, but light absorption and thus short-circuit current densities are still limited [1]. However, the implementation of strong substrate textures for light trapping has been shown to be detrimental for solar cell performance [2]. Therefore, it is highly desirable to design interlayers that act optically rough, but ensure a smooth silicon interface in order to preserve a high material quality. Here, we present SMooth Anti-Reflective Three-Dimensionally textured (SMART) substrates which consist of SiOx-TiOx photonic crystal lattices for LPC silicon solar cells. The structures are fabricated by combining nanoimprint-lithography and spin-coating of silica and titania sol-gels. The optical response of such SMART structures is optimized experimentally and numerically, demonstrating the capability to outperform standard antireflective layers. First SMART substrates show a promising morphology and LPC compatibility and reveal the strong potential to achieve excellent optical properties while maintaining high silicon electronic material quality. [1] Haschke et al., SOLMAT 128, 190 - 197 (2014) [2] Preidel et al., JAP 117, 225306 (2015)

Authors : Hung-Ling CHEN, Nicolas VANDAMME, Julie GOFFARD, Andrea CATTONI, Aristide LEMAITRE, Amaury DELAMARRE, Benoît BEHAGHEL, Kentaroh WATANABE, Masakazu SUGIYAMA, Jean-François GUILLEMOLES, Stéphane COLLIN
Affiliations : Laboratoire de Photonique et de Nanostructures LPN-CNRS, 91460 MARCOUSSIS, France; Institut de Recherche et Développement sur l’Energie Photovoltaïque IRDEP-EDF/CNRS/Chimie ParisTech, 78400 CHATOU, France; NextPV, RCAST and CNRS, The University of Tokyo, Meguro-ku, Tokyo 153-8904, Japan; Research Center for Advanced Science and Technology (RCAST), The University of Tokyo, Meguro-ku, Tokyo 153-8904, Japan

Resume : Record single-junction solar cells are made of 1-2 µm thick GaAs absorbers with short-circuit current (Jsc) close to 30 mA/cm². A thinner absorber would lead to rapid crystalline growth and potential cost-reduction. However, efficient light-trapping is needed to maintain high optical absorption over the whole solar spectrum, and the solar cell architecture has to be revised for optimal charge collection in ultrathin layers. We investigate 200 nm thick GaAs solar cells with a nanostructured back mirror. They exhibit broadband multi-resonant absorption. We have carried out numerical calculations based on RCWA in order to explain the physical origin of resonant modes and to optimize the structure. We predict Jsc up to 26 mA/cm². A Voc improvement is also expected thanks to photon recycling. The nanostructured silver back mirror is fabricated by Nano-Imprint Lithography (NIL), and combined with localized ohmic contacts to ensure efficient charge collection while keeping the high reflectance of the silver back mirror. The GaAs solar cells are subsequently transferred on a glass substrate. Multi-resonant photocurrent spectra are characterized by Fourier-Transform Photocurrent Spectroscopy (FTPS) with high spectral resolution. Jsc up to 22 mA/cm2 is experimentally demonstrated.

Authors : I. Pavlov 1, T. Çolakoğlu 4, F. Es 4, I. Gnilitskyi 3, O. Ilday 1, R. Turan 2,4, A. Bek 2,4
Affiliations : 1 Department of Physics, Bilkent University, 06800 Ankara, Turkey; 2 Department of Physics, Middle East Technical University, 06800 Ankara, Turkey; 3 Department of Sciences and Methods for Engineering, University of Modena and Reggio Emilia,via Amendola, 42020, Reggio Emilia, Italy; 4 Center for Solar Energy Research and Application, Middle East Technical University, Ankara, Turkey

Resume : Si-based solar cells remain the main source of solar energy in the world due to low cost of material and relatively simple, industrially well-established technology. In spite of significant progress in increasing the efficiency of these devices, for most of industrially manufactured silicon solar cells’ the efficiency remains around 20%. One of the promising ways to minimize optical absorption losses for high efficiency Si-based photovoltaic device is photonic design of the front surfaces. The surface texturing causes light trapping into the device, due to light interaction with micro- nano-structured surfaces, thus increase in effective light path. However, the most of proposed methods for Si surface modification do not match industrial production requirements: such as fast manufacturing, environmental issues, and low cost per watt for final devices. Recently, it was developed a new method, Nonlinear Laser Lithography (NLL) for laser-induced periodic surface structuring, which allows nanostructuring of indefinitely large areas of many materials by excellent periodicity and uniformity. Given that NLL is a low-cost, single-step and high-speed technique, there is significant potential for solar cell applications. In present work we report the creation of photonic structure on Si-based solar cells by using NLL technique. As a laser source we used home-made 1 MHz femtosecond laser system, which can generate up to 1 μJ of pulse energy with ~120 fs of pulse duration. The laser beam was focused on Si surface and raster scanned with galvo-scanner to obtain area 1x1 cm2. Much larger areas were obtained by translating the sample with translation stage under galvo-scanner. In our work the structured area was 3x3 cm2. From SEM analysis the period of the structure is found to be around 800 nm. The sample was single crystalline p-doped Si wafer, with 4 Ω·cm resistivity and thickness of 275 μm. The solar cells were produced on the same Si wafer for both structured and unstructured areas under the same production conditions. The p-n junction was formed by phosphorous diffusion in doping furnace. The final step was back and front surface metallization in order to form electrical contacts. In conclusion, we proposed and experimentally demonstrated the recently invented NLL technique as a low-cost, high-speed, single-step technique for texturing front surface of Si-based solar cells periodically. After first experiments, the efficiency value of 10.2% were measured for control Si solar cell upon which texturing were not applied. On the other hand, surface textured Silicon solar cells by NLL performed with 12.4% efficiency which shows that the fast and cheap texturing with NLL obviously is efficient in increasing the solar cell efficiency for Si-based solar cells.

Authors : J. Valenta (a), M. Greben (a), S. Gutsch (b), D. Hiller (b), M. Zacharias (b), and M. Fujii (c)
Affiliations : (a) Department of Chemical Physics & Optics, Faculty of Mathematics & Physics, Charles University, Prague, Czechia, (b) Faculty of Engineering, IMTEK, Albert-Ludwigs-University Freiburg, Germany, (c) Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, Japan.

Resume : Absorption cross-section (ACS) of silicon nanocrystals (SiNCs) is determined via two completely independent approaches: (i) Excitation-intensity-dependent photoluminescence (PL) kinetics under modulated (long square pulses) pumping and (ii) absorbance measurements combined with morphology information obtained by the high-resolution transmission electron microscopy. This unique comparison reveals consistent ACS values around 10^(-15) cm^2 for violet excitation of SiNCs of about 3–5 nm in diameter and this value is comparable to most of direct band-gap semiconductor nanocrystals; however, it decreases steeply towards longer wavelengths. Moreover, we analyze the PL-modulation technique in detail and propose an improved experimental procedure which enables simpler implementation of this method to determine ACS of various (nano)materials in both solid and liquid states [1]. Our experimental results are compared to available literature data, including theoretical calculations. The results show that we can actually gain absorption per Si volume by forming nanocrystals but the absorption per total nanocomposite (NCs and surrounding matrix) volume is lower than for bulk Si. Therefore we should prepare more complex nanostructures like nanowires or plasmonic structures in order to address applications of Si-nanocomposites in photovoltaics. [1] J. Valenta et al. Appl. Phys. Lett. 108 (2016) 023102.

Advanced Characterization II : Ivan Gordon
Authors : Laura Schelhas1, Jeffrey Christians2, Joseph M. Luther2, Joseph J. Berry2, Michael Toney1, Chris Tassone1, Kevin Stone1
Affiliations : 1. SSRL Materials Science Division, SLAC National Accelerator Laboratory, Menlo Park, CA 2. National Renewable Energy Laboratory, Golden, CO

Resume : Methylammonium Lead Iodide (CH3NH3PbI3) organic-inorganic perovskite films are a promising absorber material with solar cell efficiencies now in excess of 21%. A significant appeal of these materials is their facile synthesis using solution processes. Typically a low temperature anneal (about 100 °C) is involved in film synthesis with subsequent cooling through the cubic-to-tetragonal phase transition near 65 °C. Since the transition temperature is within the range expected in real world device applications, it is therefore important to understand the structural behavior at this transition and its impact on the device performance. In order to better understand this phase transition in thin films, we have developed the capability for operando synchrotron X-ray diffraction by designing a sample stage for simultaneous, temperature dependent measurement of J-V curves and diffraction. This has allowed us to obtain X-ray diffraction data during the operation of CH3NH3PbI3 devices. Here we will present detailed structural characterization of the perovskite crystal structure with increasing temperature, including the tetragonal lattice distortion, octahedral rotations associated with the room temperature tetragonal phase, and thermal (disorder) parameters. The impact of these structural changes on the device J-V characteristics will be described and we comment on potential implications for material and device properties.

Authors : Sebastian Wood, Daniel O’Connor, Christopher W Jones, James Claverley, James Blakesley, Claudiu Giusca, and Fernando Castro
Affiliations : National Physical Laboratory, Teddington, Middlesex, TW11 0LW, UK

Resume : Defects in printed solar cells such as organic and organic-inorganic perovskite photovoltaics have a significant impact on the device performance, which is critical for the commercial viability of large-area manufacture. The characterisation of the various types of defects that occur in these devices is, therefore, important for identifying those which are critical to device performance and must be controlled during manufacture. This work uses a combination of dimensional surface measurements and functional mapping in order to relate the physical properties of various defects to their impact of photovoltaic properties. In particular, we demonstrate spatially resolved (~ 50 µm resolution) transient photovoltage and photocurrent measurements as a probe for local variations in charge recombination and extraction rates. Reference samples are prepared by depositing silica microspheres prior to deposition of the active layer to simulate dust contamination. These result in a local reduction in the steady state photocurrent generation and an increase in the transient photocurrent decay time, which we interpret as a reduction in the charge extraction rate. By applying this novel technique to real defects in both organic and perovskite photovoltaic solar cells we are able to draw new insights into the local charge carrier dynamics with important implications for the management of defects in large-scale printed photovoltaics.

Authors : Andreas Kaltzoglou, Dorothea Perganti, Maria Antoniadou, Athanassios G. Kontos, Polycarpos Falaras*
Affiliations : Institute of Nanoscience and Nanotechnology, NCSR Demokritos, 15310, Athens, Greece Tel.: +30 210 6503644, Fax: +30 210 6511766, E-mail:

Resume : Stress tests on third generation photovoltaic systems using inorganic Sn4+ perovskites as hole-transporting materials are reported. Dye-sensitized solar cells were fabricated with air-stable Cs2SnI6 and Cs2SnBr3I3 compounds, deposited upon photosensitized titania substrates with metal-organic dyes. The devices were tested under prolonged exposure to intense light and temperatures up to 80 ºC to simulate realistic operating conditions. Chemical and morphological changes of the perovskites were monitored with powder X-ray diffraction and in-situ micro-Raman spectroscopy whereas the photochemical characteristics of the devices were monitored with J-V measurements and electrochemical impedance spectroscopy. The effects of the light-soaking and thermal tests on the perovskite structure and on the power conversion efficiency are discussed.

Authors : Sibel Y. Leblebici1,2, Linn Leppert1,3, Yanbo Li4, Sebastian E. Reyes-Lillo1,3, Sebastian Wickenburg1, Ed Wong1, Jiye Lee1, Mauro Melli1, Dominik Ziegler1,5, Daniel K. Angell1, D. Frank Ogletree1, Paul D. Ashby1, Francesca M. Toma4, Jeffrey B. Neaton1,3, Ian D. Sharp4, Alexander Weber-Bargioni1
Affiliations : 1The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States. 2Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California 94720, United States. 3Department of Physics, University of California, Berkeley, Berkeley, California 94720, United States. 4Joint Center for Artificial Photosynthesis and Chemical Science Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States. 5Scuba Probe Technologies LLC, 255 Lina Ave, Alameda, California 94501, United States.

Resume : : Photovoltaics based on hybrid perovskite materials have exceeded 20% efficiency in only a few years of optimization, for reasons generally ascribed to large charge carrier mobilities and lifetimes. Although functional properties, such as mobilities, photocurrent generation, and open circuit voltage are influenced by the microscopic structure and orientation of the perovskite crystals, these properties are difficult to quantify on the intragrain length scale and are often treated as homogenous within the active layer. In this work, we mapped the local short circuit photocurrent, open circuit photovoltage, and dark drift current in state-of-the-art methylammonium lead iodide solar cells with sub 30 nm spatial resolution using photoconductive atomic force microscopy. We find, within individual grains, spatially-correlated heterogeneity in short circuit current of up to an order of magnitude and in the open circuit voltage up to 0.6 V. These variations are related to different crystal facets and have a direct impact on the macroscopic power conversion efficiency of these materials. We attribute this heterogeneity to a facet-dependent density of trap states. These results imply that controlling crystal grain and facet orientation will enable a systematic optimization of polycrystalline and single crystal devices for photovoltaic and lighting applications.

Authors : Hye Ri Jung1, Gee Yeong Kim1, and William Jo1, Won Seok Woo2, Chang Won Ahn2, Shinuk Cho2, and Ill Won Kim2
Affiliations : 1Department of physics, Ewha Womans University, Seoul, 03760, Korea 2Department of Physics and Energy Harvest-Storage Research Center, University of Ulsan, Ulsan 44610, Korea

Resume : Organic-inorganic hybrid perovskite, MAPbX3 (MA=CH3NH3+, X=Br¬- or I-), single crystals are studied for elucidating their intrinsic physical properties. Concerns on grain boundaries in perovskite solar cells have been alleviated by the reports of several groups [1,2]. However, the grains are yet not fully controlled in terms of compositions, textures, and even believed as a trapping source of ionic migration. We report our observations on the distribution of surface electric potential and current transport on the two single crystals with iodine and bromine by Kelvin probe force microscopy and conductive atomic force microscopy, respectively. Surface potential exhibits about 4.7 eV, which is a similar value for thin-film perovskites [2]. Current level of the grain-boundary free large grains is smaller than thin-films but some spots exhibit large current values at high external voltage bias. Piezoelectric force microscopic measurement on the perovskite single crystals was also performed to decipher the potential ferroelectric properties or inequivalent majority/minority carrier dynamics. [1] Yun, J. S.; Ho-Baillie, A.; Huang, S.; Woo, S. H.; Heo, Y.; Seidel, J.; Huang, F.; Cheng, Y.-B.; Green, M. A. J. Phys. Chem. Lett. 2015, 6, 875. [2] Kim, G. Y.; Oh, S. H.; Nguyen, B. P.; Jo, W.; Kim, B. J.; Lee, D. G.; Jung, H. S.; J. Phys. Chem. Lett. 2015, 6, 2355.

Authors : Laia Arqués-Farré 1, Ibbi Y. Ahmet 2, Florian Oliva 1, Maxim Guc 1, Marcel Placidi 1, Tariq Jawhari 3, Lorenzo Calvo-Barrio 3,4, Xavier Alcobé 3, Edgardo Saucedo 1, Alejandro Pérez-Rodríguez 1,4, Andrew L. Johnson 2, Victor Izquierdo-Roca 1
Affiliations : 1 Catalonia Institute for Energy Research (IREC), Sant Adrià del Besòs-Barcelona, Jardins de les Dones de Negre 1 2pl., 08930, Spain. 2 Department of Chemistry and Centre for Sustainable Chemical Technologies, University of Bath, Claverton Down, Bath, BA2 7AY, United Kingdom. 3 Centres Cientifics i Tecnologics CCiTUB, Universitat de Barcelona, C. Lluis Sole i Sabarís 1, 08028, Barcelona, Spain. 4 IN2UB, Departament d’Electrònica, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, Spain.

Resume : SnS has attracted the attention of the PV community due to the combination of its desirable optical properties (direct band gap of 1.37 eV, and absorption coefficient of >105 cm-1) with binary and abundant elemental composition, which in theory simplifies its synthesis. However, currently the best SnS based PV device efficiency is 4.36 %. Limited performance is attributed to band gap alignment issues, doping content (controlled by Sn/S ratio) and poor film morphologies (due to the anisotropic structure). In this context Raman spectroscopy (RS) analysis could be useful, as it facilitates the accurate evaluation of material properties, as demonstrated in defect studies of other chalcogenide materials. We present an RS study, supported by XRD and XPS analyses, of cubic and α-SnS films grown by CVD single source precursor. In particular a complete analysis of SnS vibrational properties has been made using 7 excitation wavelengths (from UV to IR). The study describes, with high accuracy, the clear differences in Raman modes of both polymorphs: 7 or 4 peaks for cubic or α-SnS structures, respectively. Depending on the chosen excitation wavelength, pre-resonant behaviors are observed. Additionally the impact of various Sn/S ratios on Raman shift and band broadening has been evaluated and discussed. A clear RS feature dependence with composition has been observed. A methodology for accurate Sn/S ratio evaluation by RS is presented which will be relevant for SnS solar cell improvement.

Authors : A. Devos1,2, A. Le Louarn2, P. Emery2
Affiliations : 1- IEMN Dpt ISEN, 41 boulevard Vauban, 59046 Lille CEDEX, France 2- MENAPiC, 41 boulevard Vauban, 59046 Lille, France

Resume : Increased efforts are being made to develop measurement methods for novel solar cells especially on thin-film and organic solar cell technologies. In these technologies, transparent and opaque thin-film materials are combined in especially complex stacks. Thickness, composition and adhesion at interfaces must be controlled if possible in a non destructive way. This paper presents some applications to such characterizations of the APiC technology, a unique combination of optics and acoustics, which implements a SONAR at nanoscale using an ultrafast laser. Very high frequency acoustic waves are emitted and detected using such laser pulses. These waves propagate indifferently in transparent or opaque materials. These “hypersonic waves” have such a short wavelength that they suit very well the characterization of thin films, multi-layers, nanostructures and interfaces. High frequency acoustic waves are also very sensitive to interface quality. By analyzing the acoustic transmission or reflection at an interface we can detect a delamination between a film and a substrate or between two films. In this paper, we will present some results to show useful can be the APiC technique for controlling thin-film thickness and adhesion at interface in various samples issued from different thin-film photovoltaic technologies (amorphous and crystalline silicon, CIGS and organic).

Start atSubject View AllNum.Add
Advanced Characterization III : Raphael Niepelt
Authors : Martin Schubert
Affiliations : Fraunhofer-Institut für Solare Energiesysteme ISE

Resume : The measurement of photoluminescence for solar cell characterisation has become one of the most fruitful sources of information about material quality and solar cell performance. Its remarkably high sensitivity even for silicon and its non-destructive nature gave way to a wide range of applications in research and industry. Depending on the needs for resolution, measurement time and accuracy camera or microscopy based approaches have been developed. These may not only determine material parameters like carrier lifetime, doping concentration, concentration of several specific impurities, crystal defects, or trap density but also solar cell properties like local voltage and current, series resistance, or interface recombination. This presentation gives insight in the basics and advanced principles of PL based quantitative material and cell analysis with a focus on its application to silicon. It compares the strengths of different modes from steady state to time-correlated single photon counting. Current developments in the field of defect characterisation and cell analysis are presented. Specifically, injection- and temperature dependent carrier lifetime imaging for defect identification and time resolved measurements for surface recombination analysis are discussed which show the great potential of PL.

Authors : J. F. Galisteo-López, M. Anaya, M.E. Calvo and H. Míguez
Affiliations : Instituto de Ciencia de Materiales de Sevilla (ICMS-CSIC), c/Américo Vespucio 49, 41092 Sevilla, Spain

Resume : Third generation photovoltaics have witnessed the irruption of hybrid organic-inorganic perovskites as an unrivalled light harvester. [1] The rapidly achieved breakthroughs, comprising devices with high power conversion efficiencies, are beginning to be accompanied by fundamental studies necessary for turning the current rush into a mature technology. Research efforts aiming at a better understanding of the electrical, structural and photophysical properties of this material are of utmost importance, as they will bridge the gap between the as-prepared material and realistic marketable devices with excellent performances. In this work we present an in-depth analysis regarding the photophysical properties of the methylammonium lead tri-iodide perovskite (CH3NH3PbI3) as a tool for both, understanding the formation of the material itself and its performance under different environmental conditions. Performing a combined study of in-situ structural and photophysical properties during the annealing of CH3NH3PbI3 upon spin-coating the precursor solution we are able to unveil different stages of the crystallization process where nucleation and growth of perovskite crystals dominate. [2] Our results represent a clear evidence of these two processes, opening a new path for improving the properties of the material by acting on the appropriate formation stage. Beyond its use as a tool to understand its formation, the photophysics of CH3NH3PbI3 have proved fundamental in understanding how the material interacts with its environment under device operation conditions. We have identified two different reversible processes in the form of photoinduced activation and darkening of the photoluminescence, extremely dependent on the atmosphere where the films are placed. [3] We resolve the role of oxygen and moisture in the photoactivation and photodarkening, respectively. Indeed, oxygen is revealed as decisive for the emission recovery after a fatigue of the PL in perovskite films. Our results thus tackle two aspects of the physical properties of CH3NH3PbI3, which strongly determine their performance. The extracted conclusions provide insights concerning crystallization and stability of the CH3NH3PbI3 films, which allow bringing this material closer to technological applications. References: [1]. Stranks, S. D. and Snaith, H. J. Nat. Nanotechnol. 10, 391-402 (2015). [2]. Anaya, M., Galisteo-López, J. F., Calvo, M. E., López, C. and Míguez, H. J. Phys. Chem. C 2016 (Accepted). [3]. Galisteo-López, J. F., Anaya, M., Calvo, M. E. and Míguez, H. J. Phys. Chem. Lett. 6, 2200-2205 (2015).

Authors : A.S. Gudovskikh, K.S. Zelentsov, A.I. Baranov, D.A. Kudryashov, I.A. Morozov, E.V. Nikitina, J.-P. Kleider*
Affiliations : St Petersburg Academic University Russian Academy of Sciences, Hlopina str. 8/3, 194021, St.-Petersburg, Russia *GeePs, Group of electrical engineering - Paris, CNRS, CentraleSupélec, Univ. Paris-Sud, Université Paris-Saclay Sorbonne Universités, UPMC Univ Paris 06

Resume : GaP/Si heterojunctions are of great interest for photovoltaic applications. GaP has a gap of 2.26 eV with the smallest lattice mismatch beyond III-V binary compounds (less 0.4 %) providing conditions for appropriate wide gap emitter for Si based subcell as well as nucleation layer for III-V multijuction solar cell grown on Si substrate. However, the commonly used techniques for the growth of GaP layers such as molecular beam epitaxy (MBE) and metal organic vapor-phase epitaxy (MOVPE) require high temperatures of 800-900C at least at the initial stage for silicon oxide removing and surface reconstruction. High temperatures affect the Si wafers quality and the properties of III V/Si interface leading to low photovoltaic performance of GaP/Si heterojunctions obtained by epitaxy compared to the high efficiency a-Si:H/c-Si solar cells. The study of defects created in Si during epitaxial growth using MBE, MOVPE and ALD at different temperature will be reported in this paper. The photoluminescence (PL) and deep level transient spectroscopy (DLTS) measurements were used for defect characterization. A significant Si degradation during the high temperature MBE and MOVPE growth was demonstrated. This work was carried out in the framework of the joint Russian-French project LAMSOL supported by Ministry of Science and Education of Russian Federation (14.616.21.0040) and by PHC Kolmogorov Program (35522TL).

Advanced Materials : Martin Schubert
Authors : Raphael Niepelt (1), Sarah Kajari-Schröder (1), Rolf Brendel (1,2)
Affiliations : 1) Institute for Solar Energy Research Hamelin, Am Ohrberg 1, D-31860 Emmerthal, Germany; 2) Solar Energy Department, Institute of Solid State Physics, Leibniz Universität Hannover, Appelstraße 2, D-30167 Hannover, Germany

Resume : The impressive growth of the world wide PV market went along with significant cost reductions of crystalline silicon photovoltaics (c-Si PV), the market leading PV technology. Besides scale economies, the technological progress in the field of cell technology is rather driven by incremental improvements than by a frequent launch of revolutionary new concepts. This leads to a highly developed and well working quasi-standard in c-Si PV, the screen-printed p-type passivated emitter and rear cell (pPERC), which is already capable of conversion efficiencies above 22% and is likely to remain market-leading for years. Independent of the cell technology, kerfless wafering techniques show a high potential to further reduce the costs of crystalline silicon photovoltaics by reducing the silicon consumption. For example, the stress-induced exfoliation of thin Si layers offers the unique possibility to produce thin, kerf-free wafers directly from standard high-quality ingots. Our paper highlights recent trends in c-Si PV with a focus on pPERC. Beyond that, we discuss the potential of kerfless wafering and present solar cells from exfoliated silicon. We use an Al stressor layer to exfoliate a 70 µm thin Si wafer from a thicker wafer. 9 out of 10 cells show efficiencies above 17 %, with a champion cell exhibiting a Voc of 650 mV and an efficiency of 17.64 %. The cells are not restricted by the quality of the exfoliated material.

Authors : Ivan Gordon, Twan Bearda, Valerie Depauw, Miha Filipic, Hariharsudan Sivaramakrishnan Radhakrishnan, Kris Van Nieuwenhuysen, Menglei Xu
Affiliations : IMEC Kapeldreef 75, 3001 Leuven Belgium

Resume : Foil creation by lifting off a thin epitaxial silicon layer is a very promising technique to create substrates with a thickness below 100 µm and with almost no kerf loss, allowing to lower both the material cost per m2 and the energy payback time of silicon solar cells. This contribution first of all deals with the latest optimization of the foil fabrication in order to create foils that combine high material quality with a high detachment yield. The epitaxial foils are grown on a double layer stack of porous silicon that is formed by electrochemical etching and subsequently annealed at high temperatures. This porous silicon stack acts both as template for epitaxy and as detachment layer. The quality of the resulting epitaxial foil strongly depends on the smoothness of the resulting porous-silicon based template. Therefore, adapted annealing processes for the porous silicon stack are proposed, based on the observation that smoother surfaces and hence higher-quality foils can be obtained by annealing at lower temperatures for longer times. Furthermore, we were able to simultaneously improve the detachment yield for large-area foils. Finally, we will review in this contribution the current status of the process development and the limitations in cell performance for devices based on these epitaxial thin foils. We will highlight the challenges for both the freestanding processing into devices of these thin epitaxial foils as well as for processing of bonded foils into devices.

Authors : Wisnu Hadibrata 1,2, Firat Es 1,2, Emine Hande Ciftpinar 1,2, Arman Ayan 2, Rasit Turan 1,2,3, Selcuk Yerci 1,2
Affiliations : 1 Micro and Nanotechnology Programme, Middle East Technical University, Ankara, 06800, Turkey 2 The Center for Solar Energy Research and Applications, Middle East Technical University, Ankara, 06800, Turkey 3 The Department of Physics, Middle East Technical University, Ankara, 06800, Turkey

Resume : Thin crystalline silicon (c-Si) solar cells with thickness in the order of few tens of microns possess many attractive applications, for instance, electronic wearables, space probes and satellites thanks to their flexibility and light-weight. However, reducing the thickness of active layer of silicon solar cells leads to poor light absorption within the silicon layer, especially in the near infra-red region of the solar spectrum. The poor absorption becomes problematic for thin c-Si solar cells as it causes substantial photocurrent loss. One method to curtail the absorption loss is to incorporate light trapping structures into thin silicon. Light trapping structure of random upright pyramids has been proved to be efficient for conventional silicon solar cells; it allows for easy and inexpensive method of texturization by alkaline based solution. However, the average size of the randomized pyramids ranges from 4 ? 10 µm which is not suitable geometry for thin silicon with thicknesses less than 20 µm. Recently, periodic submicron inverted pyramids have been shown to enhance absorption in thin c-Si solar cells. In this work, we fabricated flexible thin c-Si solar cells with advanced light trapping of periodic inverted pyramids using relatively low-cost wet etching process as well as optimized random upright pyramids with maximum size of 3 µm for thin silicon. Efficiencies of more than 9% and 12.5% have been obtained for bare and textured silicon solar cells with a thickness of 30 µm, respectively. Thin c-Si solar cells were successfully attached to a polymer and removed from the host wafer. In this presentation, we will discuss the fabrication process of flexible thin c-Si solar cells along with the fabrication of the advanced light trapping structures.

Authors : P. Bellanger, J. M. Serra, O.Dahl, A.G.Ulyashin, D.Muller, S. Roques, R. Martini, M. Debucquoy, Y. Le gall, and A.Slaoui
Affiliations : P. Bellanger1, J. M. Serra2, O.Dahl3, A.G.Ulyashin4, D.Muller1, S. Roques1, R. Martini5, M. Debucquoy5, Y. Le Gall6 and A.Slaoui1 1Laboratoire des Sciences de l?Ingénieur, de l?Informatique et de l?Imagerie, ICube, University of Strasbourg-CNRS, 67037 Strasbourg, FRANCE 2Faculdade de Ciências, Universidade de Lisboa/IDL, Campo Grande, 1749-016 Lisboa, Portugal 3 SINTEF Materials and Chemistry, NO-7465, Trondheim 4SINTEF Materials and Chemistry, Department of Industrial Processes, Forskningsveien 1, P.O. Box 124 Blindern, NO-0314 Oslo, Norway 5Imec, Kapeldreef 75,B-3001, Leuven-Heverlee, Belgium 6ICUBE/DESSP 23, rue du Loess 67037 STRASBOURG Cedex

Resume : The photovoltaic solar cell industry is putting a lot of effort to reduce silicon cell thickness as a way to achieve cost reductions while taking advantage of expected high conversion efficiencies for such thicknesses. Indeed there are two positive points in this trend, i) material gains could be obtained and ii) thickness decrease allows some relaxation in terms of silicon bulk quality. Moreover, the classic process of ingot sawing cannot be a conceivable solution to produce thin silicon wafers, since more than 50 % of the silicon material will be lost during this step. In this work, we present solar cells made of thin silicon films formed at room temperature by the SLIM-cut technique using an epoxy layer. SLIMcut method consists in detaching thin monocrystalline silicon layers from a film inducing stress. In our case, a layer of epoxy is manually distributed on the surface of a monocrystalline silicon sample and annealed at 150 °C for 1h. The propagation of crack is activated by cooling the sample on an aluminum plate which is cooled by liquid Nitrogen. A relationship between the thickness of the epoxy layer and the foil has been determinated experimentally. Different structures of solar cells adapted to the silicon thin films have been performed. As an example, using silicon film of around 100 µm thick, conversion efficiencies of 14% and 16.7% were measured respectively using a conventional solar simulator and the "suns-Voc" system. Acknowledgments: The research leading to these results has received funding from the European Union Seventh Frame work programme (FP7/2007-2013) under grant agreement n°608593

Authors : Mirjam Theelen, Henk Steijvers, Klaas Bakker, Jeroen Vink, Nicolas Barreau, Erik Haverkamp
Affiliations : Mirjam Theelen, TNO/Solliance, High Tech Campus 21, 5656AE Eindhoven, The Netherlands; Henk Steijvers, TNO/Solliance, High Tech Campus 21, 5656AE Eindhoven, The Netherlands; Klaas Bakker, ECN/Solliance, High Tech Campus 21, 5656AE Eindhoven, The Netherlands; Jeroen Vink, ReRa Solutions, Blauwe Hof 7107, 6602 XN Wijchen, The Netherlands; Nicolas Barreau, Institut des Matériaux Jean Rouxel (IMN)-UMR 6502, Université de Nantes, CNRS, 2 rue de la Houssinière B.P. 32229, 44322 Nantes Cedex 3 France; Erik Haverkamp, ReRa Solutions, Blauwe Hof 7107, 6602 XN Wijchen, The Netherlands

Resume : In order to optimize long term stability of CIGS modules, their degradation behaviour should be understood and minimized. Therefore, we have designed and built two ‘hybrid’ degradation setups, in which humidity, temperature, illumination and electrical loads are all used as degradation loads on CIGS solar cells. In these setups, climate chambers are combined with illumination (illuminated areas of 40x40 and 100x100 cm2 for up to 12 and 32 samples calibrated BAA and AAA respectively according to IEC norm 60904-9 [1]), which allows real time monitoring of the degradation behaviour. Previously, experiments under elevated temperature, humidity and illumination allowed real-time monitoring of the increase in series resistance due to ZnO:Al degradation [1] as well as the identification of the shunting effects caused by the migration of alkali-elements in CIGS solar cells [2]. Recent studies showed degradation rates of CdTe modules [3] are strongly impacted by electrical state: modules kept under open circuit degraded rapidly, while modules at maximum power point conditions were stable. Therefore, electrical loads have been added to the setups, allowing exposure to both positive and negative biases. In this presentation, we will show the impact of exposure of CIGS solar cells to open circuit and maximum power point conditions, while future experiments will focus on reversibility of migration of alkali-elements in CIGS solar cells at negative voltages. [1] Theelen et al., Proc. 42th IEEE PVSC (2015) 1-6 DOI: 10.1109/PVSC.2015.7355639 [2] Theelen, et al., Prog. Photovolt: Res. Appl. 23 (2015) 537-545 [3] Sinapis et al., Proc. 42th IEEE PVSC (2015) 1-5 10.1109/PVSC.2015.7355628

Authors : Michael Saliba1, Simonetta Orlandi2, Taisuke Matsui3, Sadig Aghazada1, Marco Cavazzini2, Juan-Pablo Correa-Baena4, Peng Gao1, Rosario Scopelliti1, Edoardo Mosconi5, Klaus H. Dahmen6, Filippo De Angelis5, Antonio Abate7, Anders Hagfeldt4, Gianluca Pozzi2, Michael Graetzel7, Mohammad Khaja Nazeeruddin1
Affiliations : 1 Group for Molecular Engineering of Functional Materials, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, Lausanne CH-1015, Switzerland; 2Istituto di Scienze e Tecnologie Molecolari del Consiglio Nazionale delle Ricerche, CNR-ISTM, via Golgi 19, I-20133 Milano, Italy; 3Advanced Research Division, Materials Research Laboratory, Panasonic Corporation, 1006 Kadoma, Kadoma City, Osaka 571-8501, Japan; 4Laboratory for Photomolecular Science, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, CH-1015-Lausanne, Switzerland; 5Computational Laboratory for Hybrid Organic Photovoltaics (CLHYO), CNR-ISTM, via Elce di Sotto 8, I-06123 Perugia, Italy; 6Qatar Environment and Energy Research Institute, Qatar; 7Laboratory of Photonics and Interfaces, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, Lausanne CH-1015, Switzerland.

Resume : Recently, solution-processable perovskite solar cells (PSCs) have created much excitement with certified power conversion efficiencies (PCEs) of 21.0%[1] challenging the long-standing perception that high efficiencies must come at high costs. One major bottleneck for highest efficiency PSCs is the dearth of suitable hole transporting materials (HTMs) where the best performers are polytriarylamine polymer (PTAA) with 20.1%[2] or the small organic molecule 2,2’,7,7’-tetrakis(N,N-di-p-methoxyphenylamine)-9,9’-spirobifluorene (spiro-OMeTAD) with 19.7%[3]. In this work, we present a molecularly engineered HTM with a simple dissymmetric fluorene-dithiophene (FDT) core substituted by N,N-di-p-methoxyphenylamine donor groups, which can be easily modified, providing the blueprint for an entire generation of novel low-cost HTMs. We use FDT on state-of-the-art devices and achieve PCEs of 20.2%, the highest reported value yet, outcompeting comparable control devices with spiro-OMeTAD. Moreover, we show simulations in which the thiophene groups of the FDT bind to the perovskite in a particularly advantageous way introducing the design principle of dually functionalised HTMs, i.e. with a unit that has a particular interaction with perovskite and the unit responsible for the hole transport. Thus, we present a low-cost HTM which has the potential to replace spiro-OMeTAD[4]. [1] [2] Yang, W. S. et al. High-performance photovoltaic perovskite layers fabricated through intramolecular exchange. Science 348, 1234-1237, (2015). [3] Ahn, N. et al. Highly Reproducible Perovskite Solar Cells with Average Efficiency of 18.3% and Best Efficiency of 19.7% Fabricated via Lewis Base Adduct of Lead(II) Iodide. J Am Chem Soc 137, 8696-8699, (2015). [4] Saliba, M. et al. A molecularly engineered hole-transporting material for e cient perovskite solar cells. Nature Energy, (2016)

Authors : Joe Briscoe (1), Alessandro Resmini (2), Simona Pace (2), Xuan Li (1), Umberto Anselmi-Tamburini (2) and Steve Dunn (1)
Affiliations : 1. Materials Research Institute, Queen Mary University of London, UK; 2. Department of Chemistry, University of Pavia, Italy

Resume : Zinc oxide nanorods have been investigated as an alternative to mesoporous TiO2 for use in dye-sensitised solar cells (DSSCs) due to improved charge transport properties and a direct current pathway to the transparent electrode. However, due to the significantly lower surface area and subsequent reduction in dye loading, low current densities generally limit efficiency around or below 1 %. Here we present a method for the growth of lamellae on the surface of ZnO nanorods to produce brush-like structures which allows higher dye adsorption, leading to increased efficiency. By coating ~ 6 um long nanorods using an optimised precursor concentration for lamellae growth, a power conversion efficiency of ~2 % is achieved for cells using N719 dye and iodide-based electrolyte, which is one of the highest efficiencies reported for ZnO nanorod-based DSSCs. A number of methods are used to maximise the device efficiency. For example, it is shown that by increasing the nanorod growth time, greater length and therefore surface area is achieved. In addition, the use of a hydrogel-derived seed layer is shown to lead to a higher density of thinner nanorods, further contributing to the high surface area and therefore efficiency. Correct choice of annealing conditions is also shown to be important to improve the crystallinity of the ZnO lamellae while retaining the high surface area of the structure. Overall this study shows that a number of methods can be used to increase the surface area of ZnO nanorod arrays, including correct choice of seed layer, extended growth time, and the addition of appropriate surface structures. Combining these techniques has produced high efficiency ZnO nanorod-based devices, and higher efficiencies may be possible using these methods, for example by further increasing the nanorod length or using dyes optimised for ZnO-based devices.

Authors : Yahuitl Osorio Mayon, The Duong, Noushin Nasiri, Thomas P. White, Antonio Tricoli, Kylie R. Catchpole
Affiliations : Centre for Sustainable Energy Systems, Research School of Engineering, College of Engineering and Computer Science, Australian National University

Resume : We report perovskite solar cells with an ultra-porous TiO2 electron transport layer fabricated using flame spray pyrolysis (FSP). FSP allows rapid deposition of porous TiO2 films and could be scaled up for large area and high throughput solar cell production. An efficiency of 13.7% was achieved for a flame deposited porous TiO2 perovskite solar cell coated with 2 nm of TiO2, which is a comparable efficiency to perovskite solar cells made with the widely used spin-coated TiO2 porous layer. The porosity of the as-deposited (uncoated) flame deposited porous TiO2 film is 97% which can be reduced to any desired value by coating it with a thin layer of TiO2 that also adds mechanical stability. The perovskite easily infiltrates into the flame deposited porous TiO2 film because of its large pore size and high porosity. The flame deposited porous TiO2 solar cells could be further optimised by adjusting the perovskite deposition to add a perovskite capping layer. The results reported here demonstrate a promising approach for large scale production of perovskite solar cells.

Authors : M. Shahiduzzaman1*, K. Yamamoto1, Y. Furumoto1, T. Kuwabara1,2, K. Takahashi1,2, T. Taima1,2*
Affiliations : 1 Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan 2 Research Center for Sustainable Energy and Technology, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan

Resume : Hybrid organometal halide perovskites such as methylammonium lead iodide (CH3NH3PbI3) are a promising class of cost- and energy-efficient light absorption materials for thin-film photovoltaics. In this paper, we have discussed concerning two issues, CH3NH3PbI3 nanoparticles (NPs) and CH3NH3PbI3 nanocrystals (NCs) based perovskite solar cells. The preparation and characterization of CH3NH3PbI3 NPs on compact TiOx/indium tin oxide glass substrates using a simple spin-coating technique have been investigated. Compact-TiOx films were prepared by chemical bath deposition (CBD) according to the procedure described by Kuwabara et al. (Organic electronics 11 (2010) 1136). The CH3NH3PbI3/ ionic liquid mixture solution was prepared via adding 1 wt% of 1-hexyl-3-methylimidazolium chloride (HMImCl) in 25 wt% solution of CH3NH3PbI3 in N,N-dimethylformamide (DMF). Analysis of the resulting spin-coated films revealed that uniform spherical CH3NH3PbI3 NPs with an average diameter of 540 nm were homogeneously distributed on the compact-TiOx substrate as shown in Fig. 1 (a, b). However, addition of IL to the spin-coating solution facilitated the formation of homogenous nucleation sites and prevented rapid crystal formation of CH3NH3PbI3. Therefore, the presence of an IL resulted in uniform thin films with good morphology. Fig. 1: (a, b) The SEM images of the CH3NH3PbI3 films prepared without (w/o IL) and with (w/IL) IL. The nanoparticle based device showed power conversion efficiency (PCE) up to 2.44 %. The preliminary results are promising as it is the first report on the fabrication of solar cells based on CH3NH3PbI3 NPs. We also expect that the results will open a pathway towards a better understanding for the fabrication, modification and enhancement of the performance of solar cells with CH3NH3PbI3 NPs. In the present case, we assume a hindering effect followed by impact on charge dissociation, transport, and/or recombination on the device performances due to the residual IL content remained on the CH3NH3PbI3 NP films. Therefore, performance improvement experiments are underway to ensure the complete removal of IL-contents from the CH3NH3PbI3 NP films. And, we fabricated planar heterojunction (PHJ) type PSC with enhanced efficiency by introducing fullerene (C60) interlayers with thicknesses of 0, 3, 7 and 10 nm between air-stable amorphous compact TiOx and CH3NH3PbI3 layers. The modified morphology obtained by inclusion of C60 improved the surface energy properties of the cells in terms of enhanced photocurrent. Atomic force microscopy verified the correlation between the surface energy and phase morphology of the PHJ solar cells. The introduction of a C60 interlayer between CH3NH3PbI3 and TiOx layers increased the content of photogenerated charge carrier sites, as well as lowering the accumulation and trapping of photogenerated charges at the TiOx interface. The optimum thickness of C60 interlayer was 7 nm, for which a maximum PCE of 9.51% was obtained.


Symposium organizers
Antonin FEJFAR

IP-ASCR Cukrovarnická 10 162 00 Praha 6 Czech Republic

+420 220 318 501
Isodiana CRUPIUniversity of Palermo, DEIM

Viale delle Scienze; Building 9; I-90128 Palermo; Italy

+39 091 23860271

Kapeldreef 75, 3001 Leuven, Belgium
Kylie CATCHPOLEAustralian National University - ANU

Research School of Engineering Building 32 Australian National University, ACT 2602 Australia

+61 2 612 50874
Selçuk YERCI (Main organizer)Middle East Technical University

Electrical and Electronics Engineering Dumlupinar Blv. No:1 Cankaya / Ankara, 06800 Turkey

+90 312 2102344