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2020 Spring Meeting

Energy materials


Exotic materials and innovative concepts for photovoltaics

The success story of hybrid perovskite solar cells confirms that research on novel photovoltaic materials can produce outstanding breakthroughs. This clearly strongly supports the organization of an E-MRS symposium on novel and emerging materials and concepts for photovoltaics which will serve to make E-MRS a leader in the world in new energy materials.


This symposium will address fundamental and applied research on innovative photovoltaics materials and device integration. The focus will be on non-conventional photovoltaics, or conventional photovoltaics but with a radically new approach. Novel materials such as exotic silicon, oxides or multinary compounds, novel organic/inorganic materials will be included. It should be noted that inorganic perovskites have reached a conversion efficiency of 12.4% in 2018 (CsPbI3). All third generation and emerging concepts such as multiple carrier generation, hot carrier and intermediate band solar cells, upconversion and downconversion are of increasing relevance and will be discussed. Novel experimental synthesis and characterization techniques are of interest in this symposium. Novel contacting and packaging approaches are also of interest. Theoretical calculations of novel materials or emerging concepts are also relevant. Theoretical approaches on novel absorbers and concepts are fundamental to give directions to experimentalists in the field of photovoltaics.

Hot topics to be covered by the symposium:

  • Emerging solar cell absorbers
  • Computational design of novel materials or concepts
  • Novel solar cell devices
  • Oxide solar cells
  • Bulk photovoltaics and photogalvanic effects
  • Organic and hybrid solar cells
  • Exotic forms of silicon
  • Downshifting, downconversion, upconversion
  • Multiple carrier generation
  • Intermediate band solar cells
  • Hot carrier solar cells
  • Transparent conductive oxides
  • Innovative characterization techniques
  • New contacting and packaging approaches
  • New module approaches
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Organic PV and DSC : Mingjian Yuan
Authors : Artem Levitsky (1), Oded Nahor (1), Xiaolei Chu (2), Adam Moule (2), Gitti L. Frey (1)
Affiliations : 1 Department of Material Science and Engineering, Technion Israel Institute of Technology, Haifa, Israel 2 Department of Chemical Engineering, University of California Davis, CA, USA

Resume : The understanding of processing-structure-properties relationship in organic solar cells is severely limited by lack of experimental tools suitable for characterizing the bulk heterojunction (BHJ) morphology. More specifically, techniques that rely on order are impractical for the disordered domains abundant in the film; surface analysis techniques do not necessarily represent the underlying bulk structure, and the all-organic composition imposes inherent low z-contrast hindering imaging by electron microscopy. Recently, we suggested the use of vapor phase infiltration (VPI) to characterize the internal morphology of organic solar cells. VPI infuses inorganic materials into an organic matrix by exposure to gaseous precursors that diffuse into the film and in-situ convert to an inorganic product. The diffusion process proceeds selectively through domains with high free-volume leading to inorganic deposition selectively along the diffusion paths. The diffusion network is easily visualized using electron microscopy because of the high contrast between the organic matrix and the accumulated inorganic phase. This labelling approach is in concept similar to the staining approach used to image low contrast biological specimens in electron microscopy. Furthermore, the inorganic phase deposited in the organic film also provides material stability for HRTEM imaging and tomography. We used this newmethodology to characterize the morphologies polymer:fullerene and polymer:non-fullerene BHJs as a function of composition, thermal treatments and processing technique. We were able to visualize crucial characteristics of BHJ morphologies, such as domains size, shape and distribution, 3D-connectivity and interface area through fast and straightforward HRSEM and more advanced HRTEM imaging and tomography. The spatial mapping of the phase morphology and the phase behavior of each system were then correlated with device performances to provide insight on the processing-structure-property relationship towards directing improved devices.

Affiliations : The Chinese University of Hong Kong

Resume : Fused-ring electron acceptors (FREAs) based organic solar cells (OSCs) play a critical role in pushing the power conversion efficiency (PCE) of organic photovoltaics. Thin film morphology of the FREAs is extensively studied as one of the determinants of device performance. Here we report the bimodal packing motif of high crystallized FREA – IDIC and the manipulation on the molecular orientation transition achieved simply by ternary mixing with donor FTAZ and INIC3, another popular FREA. IDIC changed from dominant face-on orientation in binary FTAZ:IDIC film to a pronounced edge-on orientation in ternary FTAZ:IDIC:INIC3 films. Albeit previous regarded “unfavorable” edge-on orientation, IDIC can provide abundant in-plane electron channels created by long range backbone stacking, evidenced by the enhanced in-plane electron mobility of the ternary blend film. Combined with better exciton utilization by the energy transfer from edge-on IDIC to face-on oriented INIC3, improved ternary device efficiency of 12.5% was achieved with higher JSC and less VOC loss compared to its binary counterparts. The molecular orientation tuning by ternary mixing indicated that face-on orientation of FREA is not a must in high-performance OSCs if there existed efficient electron pathways. It gives us new insight on the morphology configuration of FREAs and provides guidance to design and optimization of high efficiency OSCs.

Authors : A. Brodu, C. Ducros, C. Dublanche-Tixier, C. Seydoux, G. Finazzi
Affiliations : Univ. Grenoble Alpes, CEA, LITEN, DTNM, LCH, 17 rue des martyrs 38054 GRENOBLE Cedex 9, France ; Univ. Grenoble Alpes, CEA, LITEN, DTNM, LCH, 17 rue des martyrs 38054 GRENOBLE Cedex 9, France ; Univ. Limoges, IRCER, UMR 7315, 16 rue Atlantis, 87068 Limoges cedex, France ; Université Grenoble Alpes (UGA), Centre National de la Recherche Scientifique (CNRS), Commissariat à l'Énergie Atomique et aux Énergies Alternatives (CEA), Institut National de la Recherche Agronomique (INRA), Laboratoire de Physiologie Cellulaire et Végétale, UMR 5168, Institut de Biosciences et Biotechnologie de Grenoble (BIG), CEA-Grenoble, 17 rue des martyrs 38054 GRENOBLE Cedex 9, France ; Université Grenoble Alpes (UGA), Centre National de la Recherche Scientifique (CNRS), Commissariat à l'Énergie Atomique et aux Énergies Alternatives (CEA), Institut National de la Recherche Agronomique (INRA), Laboratoire de Physiologie Cellulaire et Végétale, UMR 5168, Institut de Biosciences et Biotechnologie de Grenoble (BIG), CEA-Grenoble, 17 rue des martyrs 38054 GRENOBLE Cedex 9, France

Resume : One of the main limitations of microalgae culture is the low efficiency of sunlight conversion. If the culture takes place in a closed medium, a photobioreactor, another limitation is the energy consumption. To improve the overall photoconversion efficiency and provide energy support, photobioreactors (PBR) could be coupled with photovoltaic technology (PV). Specific semi-transparent photovoltaic technology could be directly placed on the PBR’s surface. PV cells absorb a part of the incident light to produce electricity while being transparent in a specific wavelength range used for photosynthesis and needed for microalgae growth. In this study, three semitransparent PV technologies were tested: hydrogenated amorphous silicon (a-Si:H) thin films and two organic cells. The photosynthesis peaks of microalgae correspond to wavelength ranges [400–500 nm] and [550–700 nm]. In these ranges, the organic ZnO/PVD4610:PCBM/HTL (PVD) cell presents the best transparency (30.1%) closed to another organic ZnO/P3HT:PCBM/HTL (P3HT) cell (29.2%). The a-Si:H solar cell presents the lower transparency (22.1%) because the first peak of photosynthesis is absorbed. From an electrical point of view, the PV efficiency is 3% for PVD, 5% for P3HT and 4% for a-Si:H. The influence of these solar cells on the microalgae production rate was investigated. The growing test showed that despite their transparency, the microalgae growth remains as without optical filtering.

Authors : Alekos Segalina*(1), Simone Piccinin(2), Dario Rocca(1),Sebastien Lebegue(1), Xavier Assfeld(1) and Mariachiara Pastore(1)
Affiliations : (1) Université de Lorraine & CNRS, Laboratoire de Phisique et Chimie Théoriques (LPCT), France (2) CNR-IOM DEMOCRITOS c/o SISSA, Italy

Resume : P-type dye-sensitized solar cells (DSCs) offer the possibility to directly convert sunlight into electrical energy at low cost. However, these devices have rather poor efficiencies compared to the n-type DSCs for reasons that are not yet clarified (slow hole injection, fast back recombination pathways)[1,2]. P-type DSCs are based on the hole injection from the HOMO of the photoexcited dye (e.g. C343) into the valence band of a semiconductor (e.g. NiO) and the driving force (the difference between the VB energy and the HOMO energy) has a key role on the overall efficiency of the DSCs[1,2]. Experimentally, the electrolyte composition was found to affect the driving force for hole injection, with small intercalating Li+ cations yielding larger effects compared to larger-sized cations[3,4]. Here, we study the effects on the energy levels lining up of Li+ salts in the electrolyte at the C343@NiO/water interface developing a multilevel approach based on first principles (DFT) molecular dynamic (MD), DFT calculations and many body perturbation theory (GW calculations). [1] Pastore, M. et al. J. Phys. Chem. C 2017, 121 (40), 22286–22294. [2] Pavone, M. et al. Phys. Chem. Chem. Phys. 2015, 17 (18), 12238–12246. [3] Luo, G. et al. Chem. Rev. 2015, 115 (5), 2136–2173. [4] Lindquist, S.-E. et al. J. Phys. Chem. B 1997, 101 (39), 7717–7722.

11:45 LUNCH    
Hybrid perovskites (I) : Gitti Frey
Authors : Mingjian Yuan
Affiliations : Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), Renewable Energy Conversion and Storage Center (RECAST), College of Chemistry, Nankai University, Tianjin 300071, P. R. China

Resume : Reduced-dimensional (quasi-2D) perovskites have attracted widespread of attention recently, owing to its superior semiconducting properties. As far as we know, multiple -value species are created during the crystallization. Accordingly, efficient cascade energy transfer takes place among different -value species, and the carriers would eventually concentrate to the lowest bandgap specie. Great success has accomplished in perovskite light-emitting diodes (PeLEDs) and photovoltaics by taking advantage of this phenomenon. Here, I will summarize the recent progress in our group towards efficient optoelectronics including photovoltaics, LEDs and detectors using quasi-2D perovskites.

Authors : Ying-Chiao Wang,*1 Shao-Ku Huang,2 Toshihiro Nakamura,3 Yu-Ting Kao,4 Chun-Hao Chiang,2 Di-Yan Wang,4 Yuan Jay Chang,4 Nobuyoshi Koshida,5 Toshikazu Shimada,5 Shihao Liu,1 Chun-Wei Chen,2,6 and Kazuhito Tsukagoshi*1
Affiliations : 1. International Center for Young Scientists (ICYS) & WPI International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), Tsukuba, Ibaraki 305-0044, Japan; 2. Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan; 3. Department of Electrical and Electronic Engineering, Hosei University, Koganei, Tokyo 184-8584, Japan; 4. Department of Chemistry, Tunghai University, Taichung 40704, Taiwan; 5. Quantum14, Ltd., Higashi-Koganei Jigyosozo Center, Koganei, Tokyo 184-0002, Japan; 6. Center of Atomic Initiative for New Materials (AI‐MAT), National Taiwan University, Taipei 10617, Taiwan

Resume : Further boosting power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) without excessively increasing production expenses is critical to practical applications. Here, we introduce silicon quantum dots (SiQDs) to assist perovskites to harvest additional sunlight without changing PSC processes. These SiQDs could convert shorter wavelength excitation light (300-530 nm) into visible region, and meanwhile could reflect longer wavelength perovskite-unabsorbed visible light (550-800 nm), leading to broadband light absorption enhancement in PSCs. As a result, SiQD-based photocurrent gainers could improve external quantum efficiencies of PSCs over a wide wavelength range of 360-760 nm, yielding the relative enhanced short-circuit current density ( 1.66 mA/cm2) and PCE ( 1.4%). Surprisingly, even the PSC with low purity perovskites shows an ultra-high PCE improvement of 5.6% up. Our findings demonstrate QD-assisted effects incorporating earth-abundant and environmentally-friendly silicon bring effective optical management that remarkably promote performances of PSCs and enable address their substantial balance of costs.

Authors : Maryline Ralaiarisoa*(1), Mathieu Frégnaux(2), Armelle Yaïche(3), Jean Rousset(3), Muriel Bouttemy(2), Arnaud Etcheberry(2), Philip Schulz(1)
Affiliations : (1)CNRS, Institut Photovoltaïque d’Île de France (IPVF), UMR 9006, 18 boulevard Thomas Gobert, 91120, Palaiseau, France; (2)Institut Lavoisier de Versailles (ILV), Université de Versailles Saint-Quentin en Yvelines, Université Paris-Saclay CNRS, 45 avenue des Etats-Unis, 78035 Versailles, France; (3)EDF R&D, Institut Photovoltaïque d’Île de France (IPVF), 18 boulevard Thomas Gobert, 91120, Palaiseau, France

Resume : The long-term viability of perovskite-based solar cells is contingent on the evolution of their performance and the improvement of their stability, which primarily require a thorough understanding of device property-function relationships. Electronic and chemical properties at the interfaces are particularly relevant for the device functionality since they ultimately impact the charge transport at the different interfaces throughout the device. Still, an accurate understanding of the mechanisms governing during device operation requires a controlled monitoring of the respective layers’ electronic properties in an operando fashion, i.e. while indispensable biases such as light and voltage are applied. In our study, to establish an X-ray photoelectron spectroscopy (XPS) operando procedure, we primarily design and investigate perovskite half-devices consisting of a multi-cation mixed halide perovskite layer partially inserted between a FTO/TiO2 substrate and a Au top electrode. We consistently monitor the electronic and chemical properties across the surface of the device sample and their changes upon application of various external biases. We discuss the implication of transient and dynamic processes in these changes and the photovoltage. Moreover, we monitor the chemical reactions, that can be at the core of degradation processes in perovskite solar cells, occurring for different measurement parameters in order to disentangle their effects from those of the external biases.

Authors : M Kepenekian, X. Che, C. Katan, J. Even, I. Spanopoulos, J. Hoffman, X. Li, M. G. Kanatzidis, J.-C. Blancon, A. D. Mohite, C. C. Stoumpos, A. Leblanc, N. Mercier, C. Zheng, O. Rubel
Affiliations : Univ Rennes, ENSCR, INSA Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes) − UMR 6226, Rennes F-35000, France; Univ Rennes, INSA Rennes, CNRS, Institut FOTON − UMR 6082, Rennes F-35000, France; Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States; Department of Chemical and Biomolecular Engineering, Rice University, Houston, Texas 77005, United States; Department of Materials Science and Technology, University of Crete, Heraklion GR-70013, Greece; McMaster University, Hamilton, ON, Canada

Resume : The attention brought to halide perovskites thanks to their success in photovoltaic applications has shed new light on the impressive flexibility exhibited by those materials [1]. If 3-dimensional (3D) compounds offer limited choice over the choice of the metal or the organic cation, layered materials (2D), already known for their great optical properties, offers many opportunities for chemists to design application driven materials [2,3]. In between strictly 2D and 3D materials, there is a wealth of compounds with features of both dimensionality and intriguing properties. Among those, one can find the ‘deficient’ or ‘hollow’ perovskites [4-6], but also perovskitoids consisting of not-only corner-shared octahedra [7] down to 1D materials. Here, we will focus on this range of exotic materials. By combining experimental characterization and computational investigation on the electronic structure, we will describe the main features of these fringe materials [6-8] and propose the design of new materials [9]. [1] B. Saparov, D. B. Mitzi, Chem. Rev. 2016, 116, 4558. [2] L. Pedesseau et al., ACS Nano 2016, 10, 9776. [3] C. Katan, N. Mercier, J. Even, Chem. Rev. 2019, 119, 3140. [4] A. Leblanc et al., Angew. Chem. Int. Ed. 2017, 56, 16067. [5] I. Spanopoulos et al., J. Am. Chem. Soc. 2018, 140, 5728. [6] A. Leblanc et al., ACS Appl. Mater. Interfaces 2019, 11, 20743. [7] J. M. Hoffman et al., J. Am. Chem. Soc. 2019, 141, 10661. [8] C. Zheng, O. Rubel, M. Kepenekian, X. Rocquefelte, C. Katan, J. Chem. Phys. 2019, 151, 234704. [9] M. Kepenekian et al., Nano Lett. 2018, 18, 5603.

Authors : Sunil Kumar, Jennifer D, Naama S, Nathan D, Pierre C & N D Nguyen
Affiliations : SPIN lab, Physics Department, University of Liege

Resume : With the ever-increasing popularity and the rapid advancements in the field of perovskite solar cells, there is nowadays a need for standardized testing and analytical methods dedicated to this new generation of devices. The complex nature of these hetero-structured cells, with several functional layers at the heart of interlinked charge transport mechanisms, is associated to recombination losses which can lead to detrimental effects on the cell performances. The accurate measurement of those effects and their precise physical interpretation are key to the understanding of the correlation between device efficiency and material composition and quality. Understanding charge transport in materials can be achieved through a dedicated characterization by frequency domain techniques, such as electrochemical impedance spectroscopy (EIS), that are useful tools to characterize processes occurring on different time scales in solar cells. In this work, we successfully use EIS to compare the blocking properties of a thin TiO2 layer coated by ultra-sonic spray pyrolysis under different ambient atmospheres (air, O2 and N2) along with a commercial TiO2 suspension cured under ultra-violet light. The detailed analysis of the impedance spectra by electrical simulations suggests that the lack of oxygen during the process under N2 atmosphere could be related to a change of TiO2 quality which is ultimately responsible for enhanced charge carrier recombination at the anode and loss in cell performance. The results of this study are extended by an in-depth analysis of charge transport using an approach based on a variant of photo current spectroscopy in which the modulation of light intensity allows to capture a cell response that provides complementary information about charge carrier lifetime and electron-hole recombination dynamics.

Authors : Robert Wenisch, Ivona Kafedjiska, Rutger Schlatman, Iver Lauermann
Affiliations : Competence Centre Thin-Film and Nanotechnology for Photovoltaics Berlin, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany; Competence Centre Thin-Film and Nanotechnology for Photovoltaics Berlin, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany; Competence Centre Thin-Film and Nanotechnology for Photovoltaics Berlin, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany

Resume : RF-sputtered, non-stoichiometric NiOx is a promising inorganic p-type transparent conductor for perovskite solar cells and also for perovskite-based tandem devices. Compared to traditional organic hole transport materials it provides better long term stability and a scalable deposition method at a comparatively low price. Here, we present the material properties of RF-magnetron sputtered NiOx. The stoichiometry is varied by enriching the sputter atmosphere with O2 allowing for the variation of material properties in dependence on the O content. The samples are optically characterized by UV-vis spectroscopy yielding the wavelength-dependent refractive index and the extinction coefficient. Hall measurements give estimates for the carrier concentration and mobility. The measured optical and electrical material properties are important prerequisites for the simulation and optimization of NiOx-employing photovoltaic devices. An in-vacuum transfer from the sputter chamber to the X-ray photoelectron spectrometry system enables an unperturbed analysis of the O 1s signal giving insight on the chemical state and composition. The results are related to the chemical state of Ni as observed in its 2p spectral region.

Authors : Ching-Ting Lee1,2,3; Hsin-Ying Lee2; Kai-Cheih Chang3
Affiliations : 1. Department of Electrical Engineering, Yuan Ze University, Taoyuan 320, Taiwan, Republic of China; 2. Department of Photonics, National Cheng Kung University, Tainan 701, Taiwan, Republic of China; 3. Institute of Microelectronics, Department of Electrical Engineering, National Cheng Kung University, Tainan 701, Taiwan, Republic of China

Resume : In addition to environment pollution, energy shortage has become extremely serious crisis. Consequently, development of green renewable energy source is a very urgent research topic. Among green renewable energy sources, perovskite solar cells were developed in the past years. In the standard structure, metal oxide films were used as the hole transport layer (HTL) of perovskite solar cells. In this study, to improve performance, NiO layer and various NiO/Ag/NiO triple layers were deposited as HTL of perovskite solar cells using a radio frequency magnetron sputter. Compared with average transmission of 66.8% of the 60-nm-thick NiO HTL, the average transmission was improved to 70.4% for the NiO/Ag/NiO (30/7/30 nm) HTL. Consequently, the power conversion efficiency (PCE) of MAPbI3 perovskite solar cells using the NiO/Ag/NiO HTL was improved from 11.02% to 11.68%. To broaden light absorption, various FAxMA1-xPbI3 active layers were fabricated by blending various FAI contents with MAI. The PCE of the FA0.1MA0.9PbI3 perovskite solar cells using 60-nm-thick NiO HTL was improved to 12.30%. By integrating the optimal FA0.1MA0.9PbI3 active layer and the optimal NiO/Ag/NiO HTL, the PCE of the resulting perovskite solar cells was further improved to 12.67%. This work was supported from the Ministry of Science and Technology of the Republic of China under contract No. MOST 108-2221-E-006-215-MY3, MOST 108-2221-E-155-029-MY3, and MOST 108-2221-E-006-196-MY3.

Authors : Philip Schulz
Affiliations : CNRS, Institut Photovoltaïque d’Île de France (IPVF), UMR 9006, 18 boulevard Thomas Gobert, 91120, Palaiseau, France

Resume : In the past decade, halide perovskite (HaP)-based solar cells (PSCs) demonstrated a breakthrough in photovoltaic (PV) performance and are since the most promising emerging PV technology in the field with power conversion efficiencies of over 25%. HaPs mark an outstanding class of materials for photon absorption, but are prone to degradation due to their hybrid organic inorganic character and hence volatile components and reactive halide ions. The outstanding improvements in HaP solar cell (PSC) performance and stability can be primarily ascribed to a careful choice of the interfacial layout in the layer stack.1 Our current research efforts focus on mitigating the perovskite film decomposition caused by external stresses and device operation. By tailoring the interfaces in the PSC, we were able to achieve over 1000 h of continuous operation without additional encapsulation. Here, the stability was correlated to suppressed ion migration in the HaP layer evidenced by time-of-flight secondary ion mass spectrometry and X-ray photoemission spectroscopy (XPS).2 In this contribution, I will detail the impact of the interface formation and novel encapsulation techniques on device performance, considering effects such as chemical reactions and surface passivation on interface energetics and stability.3 [1] Schulz, P. ACS Energy Lett. 2018, 3, 1287–1293 [2] Christians, J. A., Schulz, P. et al. Nat. Energy 2018, 3, 68–74 [3] Schulz, P.; Cahen, D.; Kahn, A. Chem. Rev. 2019, 119, 3349-3417

16:00 Break    
Poster session 1 : Thomas Fix
Authors : Steffi Antony M and Rajeshkumar Shankar Hyam
Affiliations : Department of Physics, Goa University, Goa, India

Resume : Tin-based halide perovskite solar cell with novel inverted architecture will be constructed. The free standing titanium dioxide nanotube arrays (electron transport material) will be prepared by electrochemical anodization. A thin layer of NiO film forms the hole transport layer. Solvent–based technique will be employed to prepare the Sn-based perovskite solar cells. The photon electron microscopy, X-ray diffraction, thermogravimetric analysis, PL spectra, solar simulator analysis will be carried out. The surface morphology will be studied using FESEM and AFM. The device performance will be optimized to enhance the photoconversion efficiencyof the PSCs.

Authors : Tsung-Han Yeh1; Shao-Yu Chu1; Hsin-Ying Lee1*; Ching-Ting Lee1,2
Affiliations : 1 Department of Photonics, National Cheng Kung University, Tainan 701, Taiwan, Republic of China; 2 Department of Electrical Engineering, Yuan Ze University, Taoyuan 320, Taiwan, Republic of China

Resume : The perovskite is superior to other organic materials in terms of its small absorption bandgap, small exciton binding energy, long exciton lifetime, and large carrier-diffusion length. Consequently, the perovskite solar cells have attracted much attentions. In this work, we developed a novel vanadium oxide (VOx) interface modification layer (IML) in the perovskite solar cells (PSCs) by using a radio frequency magnetron sputtering system. The inserted VOx film is a promising material to modify the interface between the ITO anode electrode and the PEDOT:PSS hole transport layer (HTL). Both material analyses and electrical measurement confirm the characteristics of the PSCs with VOx IML. According to an ultraviolet photoelectron spectroscopy spectra and the optical energy bandgap results, the VOx IML could work as an electron blocking layer and make more energy level match between the work function of ITO anode electrode and the highest occupied molecular orbital (HOMO) of PEDOT:PSS HTL. The power conversion efficiency (PCE) of the PSCs with VOx IML was enhanced from 9.43% to 13.69% in comparison with the conventional PSCs without VOx IML. It is expected that the inserted VOx film is a promising material to modify the interface between the ITO anode electrode and the PEDOT:PSS HTL. This work was supported from the Ministry of Science and Technology of the Republic of China under contract No. MOST 108-2221-E-006-196-MY3.

Authors : Shyantan Dasgupta (a,b), Kasjan Misztal(c), Rosinda Fuentes Pineda (c), Sylvester Sahayaraj (a),Robert Kudrawiec (d),Artur Herman (d),Wojciech Mroze(e),Alex Barker(e), Taimoor Ahmad (c),(f),Aldo Di Carlo (f) ,Annamaria Petrozza(e), Alina Dudkowiak (b) , Konrad Wojciechowski (a),(c)
Affiliations : a Saule Research Institute(SRI),division of Saule Technologies,11 Dunska,54-130,Wroclaw,Poland b,Faculty of technical physics,Poznan University of Technology,Piotrowo 3 street,60-965 Poznan,Poland c,Saule Tehnologies,11 Dunska,54-130,Wroclaw,Poland d,Department of Physics, Polytechnic Wroclawska, Wroclaw,Poland e Centre for Nanoscience and Technology(CNST),Instituto Italiano di Technologia (IIT),Via Pascoli,70/3,20133, Milano,Italy f Department of electronics engineering,University of Rome “Tor Vergata”,via del Polytecnico 1,00133 Rome,Italy

Resume : Perovskite materials have been explored in various fields of electronics due to its ionic conductive properties and large area processing allowance achieving nearly 25% [1] but its film formation and in turn photovoltaic performance of solar cells made from various precursor materials exhibit large dependence on the colloidal chemistry occurring in the perovskite precursor solution[2].The purity of methylammonium iodide (MAI) can have a large influence on the perovskite film formation. Particularly, the presence of trace amounts of different phosphate salts (for example methylammonium hypophosphite MAH2PO2), which is detected in most synthesized MAI powders and shown to affect the colloidal size in perovskite precursor solution and overall crystallization process of perovskite films[2][3] MAI is conventionally synthesized from methylamine and hydroiodic acid (HI) which has to be stabilized with hypophosphorus acid (HPA), a reducing agent. HPA is the source of phosphorus-containing salts in MAI. Although after recrystallization of non -purified MAI can remove most of the phosphorous acid additives, the films still suffer from rougher grains and irreproducible film formation. Here, we present the fabrication of methylammonium lead iodide (MAPbI3) perovskite films with ultra -pure MAI with no HI as reagent and with no phosphorus traces leading to films with improved spectral electroluminescence ,reduced defect concentration of 3.054x1016 cm-3 and a high PL radiative lifetime of 600ns.The PLQE and ELQE values for this MAPbI3 devices fabricated from the thin films with precursor solutions of ultra pure MAI synthesis route were also enhanced in turn leading to higher optoelectronic performances with a Power conversion efficiency(PCE) of nearly 16%. [1] US National Renewable Energy Laboratory, “Best Research-Cell Efficiencies,” Nrel. p. 1, 2019. [2] B. Podolsky et al., “References and Notes 1.,” vol. 338, no. November, pp. 643–648, 2012. [3] M. T, K. A, T. K, and S. Y, “Organometal halide perovskites as visible-light sensitizers for photovoltaic cells,” J. Am. Chem. Soc., vol. 131, no. 17, pp. 6050–1, 2009.

Authors : Corentin Paillassard, Zhelu Hu, Laurent Billot, Lionel Aigouy, Zhuoying Chen
Affiliations : Laboratoire de Physique et d'Etude des Matériaux (LPEM), ESPCI Paris, PSL Research University, Sorbonne Université, CNRS, 10 Rue Vauquelin, 75005 Paris, France

Resume : Organic-inorganic hybrid perovskite solar cells have known an unparalleled development in the last ten years. Much progress has been achieved: the solar cell power conversion efficiency has reached 25% in only a few years, while the stability of these devices still merits further improvements. For more stable perovskite solar cells, diverse techniques are currently being investigated, such as the engineering of the transport layer or the composition of the perovskite. One of the techniques is adding chemical additives to the perovskite absorber. Among different potential candidates, one of the successful ones is the thyocianate (SCN-)[1]. Generally paired with another additive, it has shown great effects on the morphology and performance of perovskite solar cells[2]. The SCN- is known for enlarging the grain size of perovskite crystals and creating a small quantities of remaining grains of PbI2, two effects that are believed to be positive for the performances of the cells[3]. In this study, we tried to differentiate the impact of these two effects and clarify the contribution of each of them in term of efficiency and stability. [1] Ke W. et al, Adv. Mater. 2016, 28, 5214–5221 [2] Zou J. et al, Electrochim. Acta 2018, 291, 297-303 [3] Cheng N. et al, Curr. Appl. Phys. 2019, 19, 25-30

Authors : Kostylyov, V.P. (1), Sachenko, A.V. (1), Vlasiuk, V.M. (1), Sokolovskyi, I.O. (1), Kobylianska, S.D. (2), Torchyniuk, P.V. (2), V'yunov, O.I. (2), Belous, A.G. (2), & Shkrebtii, A.I.* (3).
Affiliations : (1) V. Lashkaryov Institute of Semiconductor Physics (ISP), NAS of Ukraine, Kyiv, 03028, Ukraine; (2) Vernadsky Institute of General and Inorganic Chemistry, NAS of Ukraine, Kyiv, 03142, Ukraine; (3) Ontario Tech University, Oshawa, ON, L1G 0C5, Canada. *

Resume : We synthesized promising photovoltaic energy material, CH_3NH_3PbI_2.98Cl_0.02 perovskite films, and investigated their structural, photoelectric and optical properties. Films preparation method and their structural characterisations are described. Photoelectric and optical propertied were investigated by non-destructive methods using spectral characteristics of the small-signal surface photo-voltage and transmission spectra. The films were prepared by mixing of precursor reagents, dissolved in dimethyl-phthalate at 70°C for 1 hour, followed spin-coating at the glass or ITO/glass surfaces, finally the films were annealed at 90°C for 30 min. Films’ morphology can be described as randomly oriented needle-like structures that lead to a natural film profiling. Such profiling significantly increases the absorption length for longwave photon propagation, causing a red-shifts of the low-signal photo-voltage spectra. The unit cell parameters were determined from Rietveld full-profile analysis of X-ray data. The small-signal surface photo-voltage spectra were measured in the wavelength range of 400 ─ 900 nm. It was established that the spectral dependence of both the low-signal photo-voltage is determined by the spectral dependence of the external quantum output. In conclusion, the synthesized films demonstrate large diffusion length of the minority carriers, which exceeds the film thickness, and are promising for applications in photovoltaics.

Authors : Mohamed Elnaggar 1,2,3, Alexandra G. Boldyreva1, Moneim Elshobaki1, Sergey A. Tsarev1, Andrey V. Danilov4, Yury S. Fedotov4, Olga R. Yamilova1,2, Sergey I. Bredikhin4, Sergey M. Aldoshin2, Keith J. Stevenson1 and Pavel A. Troshin1,2
Affiliations : 1Skolkovo Institute of Science and Technology, Nobel St. 3, Moscow 121205, Russia 2The Institute for Problems of Chemical Physics of the Russian Academy of Sciences Semenov Prospect 1, Chernogolovka 141432, Russia 3Moscow Institute of Physics and Technology, Dolgoprudny, Moscow, Russia 4Institute of Solid State Physics of RAS, Chernogolovka, Russia. *e-mail:

Resume : Perovskite solar cells (PSCs) demonstrated impressive performances, while their operation stability still requires substantial improvements before this technology can be successfully commercialized. There is a growing evidence that stability of PSCs is strongly dependent on the interface chemistry between the absorber films and adjacent charge transport layers, while the exact mechanistic pathways remain poorly explored. Here we present a straightforward approach for decoupling the degradation effects induced by the top electron-transport layer (ETL) of PC61BM and various bottom hole-transport layer (HTL) materials assembled in p-i-n device configurations. We show that chemical interaction of MAPbI3 absorber with PC61BM most aggressively affects the operation stability of solar cells. However, washing away the degraded fullerene derivative and depositing fresh ETL leads to restoration of the initial photovoltaic performance when bottom perovskite/HTL interface is not degraded. Following this approach, we were able to compare the photostability of stacks with various HTLs. It has been shown that PEDOT:PSS and NiOx induce significant degradation of the adjacent perovskite layer under light exposure, while PTAA provides the most stable perovskite/HTL interface. ToF-SIMS analysis of fresh and aged samples allowed us to identify chemical origins of the interactions between MAPbI3 and HTLs.

Authors : Ang Li, Saif A. Haque, Thomas Macdonald
Affiliations : Department of chemistry, Imperial College London, UK

Resume : Hybrid lead halide perovskite solar cells have been the vigorous subject of emerging photovoltaics for the last decade, with booming performance and low-cost solution process.1 One challenge in advancing this encouraging technology to commercialization is the toxicity of lead. Although efforts have been devoted to substitute lead, nontoxicity is the cost of the efficiency. Currently, tin based-perovskite is the most promising alternative among lead-free options, with narrow bandgap and higher carrier mobility.2 The new star is mainly suffering from the oxidation of Sn2+ to Sn4+, which induces the self-doping and fast carrier recombination. Herein, the project focuses on the design, synthesis, and characterization of stable tin perovskite solar cells. Notably, it emphasizes on the low-dimensional tin perovskites that demonstrate the promising results of stability and device performance.3 By combining low-dimensional perovskite film with the novel organic hole-transporting materials, such hybrid heterojunctions will undergo a series of optical spectroscopic methods (steady state and time-resolved) for their stability and performance. (1) Jena, A.K. et al Chem.Rev, vol. 119, issue 5, pages 3036-3103 (2) Herz, L. M. et al ACS Energy Letters, vol 2, issue 7, pages 1539–1548 (2017) (3) Lanzetta et al ACS Energy Letters, vol 2, issue 7, pages 1662-1668

Authors : Ruslan Timerbulatov, Veronika Khalchenia, Sergey Tsarev, Sergey M. Aldoshin, Keith Stevenson, Pavel Troshin
Affiliations : Ruslan Timerbulatov (1); Veronika Khalchenia (1); Sergey Tsarev (1); Sergey M. Aldoshin (2); Keith Stevenson (1); Pavel Troshin (1,2); (1) Center for Energy Science and Technology (CEST), Skolkovo Institute of Science and Technology, 143026 3 Nobel Str. Moscow, Russian Federation; (2) The Institute for Problems of Chemical Physics of the Russian Academy of Sciences, Academician Semenov avenue 1, Chernogolovka, Moscow region, 142432 Russian Federation;

Resume : During the last decade, hybrid organic-inorganic perovskite solar cells attracted a great attention due to their outstanding performance achieved at projected low fabrication cost. Power conversion efficiency (PCE) of small-area perovskite solar cells surpassed recently 25%, which features great commercialization potential of this emerging PV technology. Among different absorber material formulations, multication systems comprising cesium, formamidinium (FA) and optionally methylammonium are now the most intensively studied due to their advanced optoelectronic properties and good stability. However, deposition of large-area films of such multication perovskites is more challenging compared to conventional MAPbI3 system. Therefore, in this work we focused on the development of reliable procedures for coating multication perovskite films and evaluation of their performance in solar cells. In particular, we explored the potential of physical (PVD) and chemical (CVD) vapor deposition techniques for growing large-area thin films of multication perovskites. Using XRD, AFM and optical spectroscopy measurements we have shown that the films with a decent morphology and the desired phase composition might be obtained by both of these methods. The application of the coated films in small- and large-area solar cells will be discussed.

Authors : Saba Gharibzadeh a,b, Ihteaz M. Hossain a,b, Paul Fassl a,b, Bahram Abdollahi Nejand a,b, Tobias Abzieher b, Moritz Schultes c, Erik Ahlswede c, Philip Jackson c, Michael Powalla c, Sören Schäfer d, Michael Rienäcker d, Tobias Wietler d, Robby Peibst e, Uli Lemmer a,b, Bryce S. Richards a,b, and Ulrich W. Paetzold a,b
Affiliations : a Institute of Microstructure Technology, Karlsruhe Institute of Technology, Hermann-von Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany b Light Technology Institute, Karlsruhe Institute of Technology, Engesserstrasse 13, 76131, Karlsruhe, Germany c Zentrum für Sonnenenergie‐ und Wasserstoff‐Forschung Baden‐Württemberg (ZSW), Meitnerstr. 1, 70563 Stuttgart, Germany d Institute for Solar Energy Research Hamelin (ISFH), Am Ohrberg 1, 31860 Emmerthal, Germany e Institute of Electronic Materials and Devices, Leibniz Universität Hannover, Schneiderberg 32, 30167 Hannover, Germany

Resume : Lead halide perovskite absorbers (APbX3) exhibit a tunable bandgap (Eg, 1.5-2.3 eV), allowing for an adjustable absorption range by just varying the halide (X = I, Br) or cation (A = FA, MA, Cs) ratio in the perovskite crystal structure. This feature makes perovskite semiconductors particularly attractive for tandem photovoltaics, in which a wide-bandgap (~1.75 eV) perovskite top solar cells combined with a low-bandgap crystalline silicon (c-Si) or a copper indium gallium diselenide (CIGS) bottom solar cell. This concept bears the potential to surpass the Shockley-Queisser limit of the single junction solar cell. However, in order to exploit this potential, the low open-circuit voltage (VOC)-to‐bandgap ratio of the wide-bandgap top perovskite solar cell (PSC) limits the advancement in this field. In this work, we employ a 2D/3D perovskite heterostructure in wide-bandgap PSCs to reduce the VOC deficit by spin-coating n-butylammonium bromide on top of double-cation perovskite absorber layers with engineered bandgaps (FA0.83Cs0.17Pb(I1-yBry)3; 0.24 ≤ y ≤ 0.56, 1.65 eV ≤ Eg ≤ 1.85 eV). Irrespective of the bandgap of the absorber, the 2D/3D heterostructure results in reduced non-radiative recombination losses at the interface of the hole transporting layer, enhancing the VOC of the PSCs by ~45 mV compared to reference devices without the heterostructure. Using this surface passivation strategy, efficient semi-transparent PSCs with engineered bandgaps are fabricated and employed in mechanically-stacked four-terminal tandem configuration based on c-Si and CIGS bottom solar cells. Thereby, prototype PSC/c-Si and PSC/CIGS tandem solar cells with stabilized PCEs of 25.7 % and 25% are demonstrated, respectively. Moreover, it is experimentally shown for the first time that a broad range of bandgaps of the top PSCs are suitable for achieving high-efficiency four-terminal tandem devices. S. Gharibzadeh, B. A. Nejand, M. Jakoby, T. Abzieher, D. Hauschild, S. Moghadamzadeh, J. A. Schwenzer, Brenner, R. Schmager, A. A. Haghighirad, L. Weinhardt, U. Lemmer, B. S. Richards, I. A. Howard, U. W. Paetzold. Advanced Energy Materials, 2019, 9. N. 21, S. 1803699. Saba Gharibzadeh, Ihteaz M. Hossain, Paul Fassl, Bahram Abdollahi Nejand, Tobias Abzieher, Moritz Schultes, Erik Ahlswede, Philip Jackson, Michael Powalla, Sören Schäfer, Michael Rienäcker, Tobias Wietler, Robby Peibst, Uli Lemmer, Bryce S. Richards, Ulrich W. Paetzold (under revision).

Authors : Veronika Khalchenia* (1), Marina Tepliakova (1), Alexander Akkuratov (2), Sergey M. Aldoshin (2), Keith J. Stevenson (1), Pavel Troshin (1,2)
Affiliations : (1) Skolkovo Institute of Science and Technology, Moscow, Russia; (2) Institute for Problems of Chemical Physics of RAS, Chernogolovka, Russia

Resume : Wide bandgap metal oxides are actively used in different technological fields including sensors, catalysts, solar cells, etc. The unique electrical and optical properties of some oxides led to extensive application of such materials as charge-transport layers in perovskite solar cells (PSCs). In this work, we systematically explored a range of metal oxide electron-transport layers (ETLs) in the context of their impact on the photostability of perovskite absorber films deposited on top. At the first stage, the behavior of simple glass/ETL/absorber bilayer stacks was studied under continuous light illumination using MAPbI3 and CsFAPbI3 as two common perovskite formulations. Then, the stability of triple-layer glass/ETL/absorber/HTL stacks was examined using polymeric hole-transport material (HTL) deposited on top of the absorber. Finally, the operational stability of completed n-i-p solar cell architectures was explored. Using such a systematic approach and a set of analytical techniques, we were able to compare the stability of different ETL/perovskite absorber interfaces and reveal correlations with the structure and properties of the oxide ETLs. The obtained results allowed us to design a perovskite solar cell with properly selected interfaces, which showed a fully stable operation within 1000 h of continuous illumination under open-circuit conditions. Thus, we believe that the results of this work provide additional impetus to the development of efficient and stable perovskite solar cells.

Authors : Edgar R. Nandayapa, Katrin Hirselandt, Dr. Christine Boeffel, Dr. Eva L. Unger, Prof. Dr. Emil J.W. List-Kratochvil
Affiliations : Helmholtz-Zentrum für Materialien und Energie GmbH, Department of Chemistry, Department of Physics & IRIS Adlershof, Humboldt-Universität zu Berlin, Fraunhofer Institute for Applied Polymer Research.

Resume : Metal halide perovskites undergo several changes when illuminated. Perovskite layers show dynamic and static photoluminescence quenching effects under low illumination densities equivalent to 1 sun, with addition to passivation effects under different atmospheric gases. For this experiment, specific partial pressures of argon, nitrogen, oxygen and water-enriched argon where tested on perovskite layers. Using the Stern-Volmer relation, we found that all these gases show a primarily static quenching effect, meaning that they are adsorbed to the crystallites. Not only that, but there is also evidence of dynamic quenching and even passivation at specific pressure ranges, measurable already at partial pressures as low as 1 mbar. Furthermore, these phenomena are mostly reversible once the quenching molecules are removed. Our observations indicate that there is an interplay between the photon flux density used to excite the material and the resulting enhancement or quenching result. In particular, oxygen and nitrogen lead to a significant but reversible static quenching, while H2O atmosphere signals a reversible dynamic process. In the case of argon, it first shows a minor PL increase at low pressures, pointing to an immediate passivation effect on the surface, yet, at higher pressures, argon still shows a moderate quenching effect. These results highlight the importance of proper sample conditioning and measurement environment before, during and after material characterization.

Authors : Itaru Raifuku, Pei-Ying Lin, Yu-Hsien Chiang, Peter Chen
Affiliations : Department of Photonics, National Cheng Kung University; Department of Photonics, National Cheng Kung University; Department of Photonics, National Cheng Kung University; Department of Photonics, National Cheng Kung University, Hierarchical Green-Energy Materials Reserch Center

Resume : Perovskite solar cells (PSCs) employing organic-inorganic perovskite materials as the light absorber have attracted much attention because of their extremely high power conversion efficiency (PCE) and solution processability. Although the PCE of first reported PSCs was only 3.8%, PCE of over 25% have achieved in the last 10 years. One of a feature of PSCs is tunable composition of the perovskite materials. Characteristics such as bandgap and stability are dramatically changed by changing the composition. For example, stability of PSCs can be improved by introducing Cs as a cation into methylammonium (MA)-formamidinium (FA) based PSCs. Here, we synthesized formamide iodide (FoAI) and tested as a novel cation material for PSCs. First, we have tested FA-FoAI mixed perovskite materials. It is known that pure FAPbI3 perovskite is instable. Actually, our FAPbI3 film was immediately degraded after exposed to ambient condition. On the other hand, FoAPbI3 films kept its original color after exposed to ambient condition for several days. Partly replaced samples, FA1-xFoAxPbI3 also showed better stability than pure FAPbI3 films. These results indicate FoAI is a promising candidate to achieve stable PSCs. Detailed characterization of FoAI based perovskite materials and photovoltaic performance will be presented at the conference.

Authors : Tianyue Wang, Qidong Tai, Guo Xuyun, Jiupeng Cao, Chun-Ki Liu, Zhu Ye, Feng Yan
Affiliations : Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.

Resume : Organic-inorganic hybrid lead based perovskite solar cells (PSCs) have aroused wide research interests for their high efficiency, which have recently achieved a power conversion efficiency (PCE) of 25.2%. However, the involvement of lead in perovskite material constitutes an obstacle for their further commercialization. Replacing lead with tin is an effective method to reduce the toxicity of PSCs, whereas Sn2+ can be easily oxidized to Sn4+, which will lead to severe p type doping and influence the device performance. Here, we report the introduction of antioxidant Gallic acid (GA) additive into FASnI3 perovskite together with excess SnCl2. By adding GA, the C-O…Sn2+ Lewis acid and base interaction between GA and SnCl2 enables the in-situ encapsulation of the perovskite grains with a co-antioxidant SnCl2-GA complex layer, which leads to improved air stability of FASnI3 perovskite. Moreover, the bandgap of SnCl2-GA complex is decreased and its conduction band is shifting downward compared to SnCl2, which facilitates electron transfer from perovskite grain through the complex layer to electron transport layer and reduces recombination loss. By systematically adjusting the amount of GA, PSCs based on the structure of ITO/NiOx/FASnI3/PCBM/BCP/Ag attain the highest PCE of 9.03% and the highest Voc of 0.64 V, which are among the highest PCE and Voc values for FASnI3-based PSCs. The FASnI3-based PSCs also exhibit striking long-term stability, which show no degradation in PCE after being stored in N2 filled glovebox for more than 1500h. And the unencapsultaed devices can maintain ~80% of its initial efficiency over 1000 h storage upon air exposure.

Authors : Marina I.Ustinova1,2, Nadezhda N. Dremova2, Sergey Yu. Luchkin1, Keith J. Stevenson1, Pavel A. Troshin1,2
Affiliations : 1Skolkovo Institute of Science and Technology, Moscow, Russia 2 Institute for Problems of Chemical Physics of RAS, Chernogolovka, Moscow region, Russia

Resume : Over the past few years, the performance of perovskite solar cells was gradually improved up to >25%, which is close to the characteristics of crystalline silicon photovoltaics. However, high toxicity and low stability of complex lead halides used as absorber materials hamper commercialization of this technology. Compositional engineering of lead halide perovskites was actively pursued in order to improve their stability and/or performance. In particular, a partial or full replacement of Pb2+ in APbX3 is highly desirable in terms of developing more environmentally friendly materials. Here we present a systematic study of lead substitution in MAPbI3, CsFAPbI3 and CsPbI3 with >20 different cations introduced in atomic concentrations ranging from 10-4 to 20-30%. It was shown that replacing even a minor fraction of lead could change significantly the perovskite film crystallinity and morphology. Importantly, the efficiency and stability of p-i-n and n-i-p solar cells were improved considerably by appropriate modification of perovskite active layer. Moreover, important relationships were established between the nature of the substituting ions (e.g. ionic radius or charge) and their effects on electronic properties and photovoltaic performance of the resulting perovskites. The obtained results should facilitate rational design of more stable and less toxic absorber materials for advanced perovskite solar cells.

Authors : Pablo Palacios, Pablo Sanchez-Palencia, Gregorio García, Perla Wahnón
Affiliations : ETSI Aeronáutica y del Espacio and Instituto de Energía Solar, Universidad Politécnica de Madrid; ETSI Telecomunicación and Instituto de Energía Solar, Universidad Politécnica de Madrid; ETSI Telecomunicación and Instituto de Energía Solar, Universidad Politécnica de Madrid ETSI Telecomunicación and Instituto de Energía Solar, Universidad Politécnica de Madrid

Resume : In this work we will identify and assess, by using quantum calculations, of the best chemical composition for inorganic halide perovskites. The general formula is ABX3, where A is an inorganic cation such as Cs which will be partially replaced by Rb or K, B = Pb+2 (the most common at inorganic halide perovskites) which will be partially replaced by Sn and X is and halide atom (Br, I). The most optimal inorganic halide perovskites will be firstly proposed based on their electronic structure. Mainly, only those materials with adequate bandgap to effectively absorbs photons from the sunlight will be chosen. In addition to electronic structure features, the stability and the lattice parameter of the proposed perovskites will be also taken into account. The stability will be measured through the Goldsmidt’s tolerance factor as well as based on thermodynamic considerations. Finally, the lattice parameter requirement is based on an effective lattice mismatch between the perovskite and different charge carrier transport materials

Authors : Zhuldyz Yelzhanova1, Gaukhar Nigmetova2, Oral Ualibek3, Bayan Daniyar1, Damir Aidarkhanov1, Askar Maxim1, Bakhytzhan Baptayev2,3, Mannix Balanay3, Aleksandra Djurisic,4 Charles Surya5, Annie Ng1,*
Affiliations : 1Department of Electrical and Computer Engineering, Nazarbayev University, Nur-Sultan, Kazakhstan 2Department of Chemistry, Nazarbayev University, Nur-Sultan, Kazakhstan 3National Laboratory of Astana, Nazarbayev University, Nur-Sultan, Kazakhstan 4Department of Physics, The University of Hong Kong, Pokfulam, Hong Kong, P. R. China 5Nazarbayev University, Nur-Sultan, Kazakhstan

Resume : Tin dioxide (SnO2) is a n-type wide bandgap semiconductor, which is commonly used as an electron transport layer (ETL) in organometal perovskite solar cells (PSCs) due to its impressive properties such as high transmittance, high electron mobility, good photostability, good energy alignment and easy processing. To facilitate the electron transport in PSCs, optimization of interface between the ETL and perovskite absorber is crucial. In this work, we aim to study the impact of SnO2 with different nanostructures on the performance of PSCs. The SnO2 nanostructures were synthesized by solvothermal technique. The effects of growth parameters including pressure, concentration of additives, growth time etc. were systematically investigated. The mixed‐halide multication perovskite solar cells were fabricated based on the nanostructured SnO2. Experimental characterizations were performed on the synthesized SnO2 material, SnO2/perovskite interface and the corresponding devices. The obtained results provide valuable insight into the community for preparing desired SnO2-ETL for high performance solar cells.

Authors : Kübra Yasaroglu1,2, Sinem Aydemir2, Sijo Chacko2, Jean-Luc Rehspringer1, Guy Schmerber1, S. Colis1, Simone Mastroianni2, Abdelilah Slaoui3, Andreas Hinsch2, Aziz Dinia1
Affiliations : 1Institut de Physique et Chimie des Matériaux, UMR UdS-CNRS 7504, Strasbourg, France 2Fraunhofer Institute for Solar Energy System ISE, Freiburg, Germany 3Laboratoire des sciences de l'ingénieur, de l'informatique et de l'imagerie, iCube UMR UdS-CNRS 7357, Strasbourg, France

Resume : Suspensions of poly(methyl methacrylate) PMMA beads with different diameter (from 80 nm to 400 nm) was used as unique templating agent to form a TiO2 scaffolded layer with controlled macro porosity by molding process. The goal was to promote the infiltration and the growth of large crystals of lead halide perovskite as light absorber materials for photovoltaic applications. A thick layer of self-assembled PMMA spheres is deposited in ROI and a Ti sol-gel solution (0.5 M) was dropped on the PMMA layer and spin-coated. After drying a carefull heat treatment at 500 °C is carried on to form the TiO2 anatase porous film. due to pores interconnection the infiltration of FA0.83Cs0.17PbBr0.8I2.2/ DMF solution is optimal. The efficiency of complete Carbon based Monolithic perovskite solar cells with different size of TiO2 porous layer was determined by I/V measurements. We obtained an improvement of efficiency of approximately 40% compare to reference cells with a record value of 14.3%. Relationship between the macro pore size and efficiency of the C-PSC is evidenced.

Authors : W. Belayachi*(1,2), S. Boujmiraz(1,3), S. Zouhair(1,3), K. Yasaroglu(1,4), G. Schmerber(1), C. Leuvrey(1), J. L. Rehspringer(1), T. Fix(5), A. Slaoui(5), M. Abd-Lefdil(2), A. Dinia(1)
Affiliations : (1) Université de Strasbourg, CNRS, Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504, 23 rue du Loess, F-67000 Strasbourg, France. (2) MANAPSE, Faculté des Sciences, Université Mohammed V de Rabat, Maroc. (3) Al Akhawayn University, Avenue Hassan II, 53000, Ifrane, Maroc. (4) Fraunhofer Instute for Solar Energy System ISE, Freiburg, Allemagne. (5) Université de Strasbourg, CNRS, Laboratoire ICube, UMR 7357, F-67000 Strasbourg, France * Email of the lead presenter:

Resume : Perovskite solar cells (PSC) have known a surge of attention from both the scientific and industrial photovoltaic community. PSCs have shown a high photovoltaic performance as they have reached a power conversion efficiency of 25.2 %. This burst of attention is mainly thanks to the numerous advantages they offer, such as their simple, easy and cheap manufacturing process. Nonetheless, they also face some limitation related to stability and degradation when in contact with humidity, and toxicity due their lead content. The goal is to study Methylammonium Lead iodide (MAPI) based PSCs with the generic formula CH3NH3[(PbI2)1-x(CuI)x]. Lead iodide (PbI2) is partially substituted by the inorganic compound Copper Iodide (CuI) to enhance the solar cell stability thanks to the hydrophobic properties of the latter. After the elaboration of the mixed perovskite material and complete solar cells, their respective structural and optoelectronic properties were identified using different characterization techniques such as, X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL), UV-Visible spectroscopy (UV), external quantum efficiency (EQE) and solar simulation. From the XRD results, it was observed that CuI was well incorporated into the perovskite lattice structure. The partial substitution showed a clear improvement of the MAPI formation. Finally, it was concluded that the highest CuI/PbI2 ratio, which is 20%, showed the best optical and PV properties.

Authors : Hagit Aviv, Yaakov Tischler
Affiliations : Department of Chemistry and Bar Ilan Institute for Nanotechnology and Advanced Materials, Bar Ilan University, Ramat Gan, 5290002, Israel

Resume : Finding renewable energy sources is of paramount importance to meet the increasing global energy demand whilst minimizing the impact on the environment. The research community has focused on solar energy as it is endlessly available, and have ranked the methylammonium lead iodide (MAPbI3) as one of the most promising candidate amongst perovskite solar cells. Despite its high efficiency, the MAPbI3 is sensitive to humidity, light, and temperature, its instability affects primarily on the crystalline structure and eventually leads to degradation. Three crystalline structures are known for this material, orthorhombic, tetragonal, and cubic which exist in different temperatures. Here we report on several processes detected from laser excitation of MAPbI3 single crystal at ambient conditions. A phase transition from tetragonal to cubic phase was induced by excitation of over 15 mW laser power. The phases were characterized by LF-Raman and photoluminescence, taken simultaneously with the increase of exciting laser power and the spectral changes were assigned to the structural differences. In addition, Raman stimulation of iodine vapors signal was observed, those vapors were generated from the core of the focus wherein the highest temperature led to degradation. The stimulated Raman phenomenon was enabled due to the unique properties of the MAPbI3 single crystal and revealed viability to use this material for additional applications in other research fields.

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Oxide solar cells and ferroelectrics : Jan Christoph Goldschmidt
Authors : Federico Rosei
Affiliations : INRS

Resume : The bulk photovoltaic effect exploits the intrinsic polarization field in ferroelectrics to separate charges upon exciton dissociation into electrons and holes. For several decades this effect was considered mostly for its fundamental interest as the power conversion efficiencies (PCE) were extremely low, mostly due to the large bandgap of most ferroelectrics and to their insulating nature. There has been a resurgent interest in this effect during the last decade, when it was shown that multiferroics, i.e. materials that exhibit two ferroic properties (in this case ferroelectricity and magnetism) exhibit higher efficiencies, mostly attributed to their smaller bandgaps [1-8]. In addition to these latest results, which brought efficiencies close to double digits [4], we also discuss the application of ferroelectric and multiferroic nanostructures for hydrogen generation [9-13]. References [1] R. Nechache et al., Appl. Phys. Lett. 98, 202902 (2011); [2] J. Chakrabartty et al., J. Am. Ceram. Soc. 97, 1837–1840 (2014); [3] J. Chakrabartty et al., Optics Express 22, A80–A89 (2014); [4] R. Nechache et al., Nature Photonics 9, 61 (2015); [5] R. Nechache et al., Nanoscale 8, 3237 (2016); [6] J. Chakrabartty et al., Nanotechnology 27, 215402 (2016); [7] W. Huang et al., J. Mater. Chem. A 5, 10355–10364 (2017); [8] J. Chakrabartty et al., Nature Phot. 12, 271–276 (2018); [9] S. Li et al., Chem. Comm. 49, 5856 (2013); [10] S. Li et al., Small 11, 4018 (2015); [11] S. Li et al., Nano Energy 35, 92–100 (2017); [12] J. Chakrabartty et al., J. Power Sources 365, 162–168 (2017); [13] W. Huang et al., ACS Appl. Mater. Int. 11, 13185–13193 (2019).

Authors : Jose J. Plata, Antonio M. Márquez, Javier Fdez. Sanz
Affiliations : Departamento de Química Física, Universidad de Sevilla, Seville, Spain

Resume : Solar energy is the most abundant source of clean and renewable energy being photovoltaics the most promising technology for the coming decades. Conventional solar cells based on p-n junctions and other new generations are good light harvesters but are limited by the Shockley-Queisser limit as carriers are separated by the internal electric field at the p-n junction. This is not the case for ferroelectric materials, which present a spontaneous electric polarization providing an alternative way to separate excited carriers. Ferroelectric oxides, as perovskites, are stable in a wide range of mechanical, chemical and thermal conditions and can be synthesized using low-cost techniques. On the other hand, these oxides usually present band gaps located higher in energy that the visible solar spectrum. New promising perovskites based on metal oxide materials absorbing in the solar spectrum have been designed using doping techniques or applying strain. Here, we present a high-throughput combinatorial approach to systematically study the effects of doping in the structural, electronic and optical properties of ferroelectric oxides such as KNbO3. To demonstrate the applicability of our framework, the 0.5(KNbO3)0.5(BaNi0.5Nb0.5O3-x) systems is used as benchmark in this work. As oxygen vacancies, Ov, are present in this material, we start by generating all inequivalent Ov distributions. In two consecutive steps, the Ba and Ni dopants distributions are also generated, obtaining all symmetry inequivalent final structures and their degeneracy. Applying high level DFT calculations, relative stabilities for all generated structures are obtained. Combining these data with their degeneracies, we are able to statistically predict the electronic and optical properties of the material at different temperatures. We believe that this systematic approach can be extended to other systems to explore and to rationalize in an automatic fashion the potential use of these doped systems as solar cells components.

Authors : L. Wendling*1, F. Gellé1, M.V. Rastei1, M. Lenertz1, G. Versini1, J.L. Rehspringer1, C. Leuvrey1, F. Roulland1, T. Fix2, A. Slaoui2, A. Dinia1, S. Colis1
Affiliations : 1 Université de Strasbourg, CNRS, Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504, 23 rue du Loess, 67034 Strasbourg, France 2 Laboratoire des Sciences de l’Ingénieur, de l’Informatique et de l’Imagerie (ICube), Université de Strasbourg, CNRS, 23 rue du Loess, 67037 Strasbourg, France

Resume : Although Si-based solar cells are widely used to convert light into electric current, their efficiency reached already 26%, close to the theoretical Shockley-Queisser limit which is about 30%. Alternative materials are expected to further improve the performances of solar cells. Among these materials, ferroelectric (FE) oxides are particularly interesting since they are highly stable and do not need a p-n junction to separate the charges as this is the case in conventional photovoltaic devices. For such applications, Bi2FeCrO6 (BFCO) double perovskite seems to be a good choice. In epitaxial films, the gap has already been modulated between 1.4 and 2.6 eV by controlling the growth conditions and by improving the Fe-Cr order.1 In order to obtain PV devices, highly Fe-Cr ordered BFCO thin films are needed along with the deep understanding of their electrical and optical properties. Epitaxial BFCO films are grown by pulsed laser deposition on SrTiO3(001) that presents a mismatch of 0.77%. The films are therefore strained on the substrate which has impact on the Fe-Cr order and the electrical properties.2 In this work, we show the influence of strains on the FE properties of BFCO with an impact on the polarization anisotropy and the FE domain polarization. Conductive-AFM measurements confirm the potential of BFCO for FE solar cells applications. [1] R. Nechache et al, Nature Photonics 9, 61 (2015). [2] M.V. Rastei et al, ACS Applied Energy Materials 2, 8550 (2019).

Authors : Alex López-García*(1), Robert Fonoll Rubio(1), Zacharie Jehl Li-Kao(1), Víctor Izquierdo-Roca(1), Alejandro Pérez-Rodríguez(1,2), Edgardo Saucedo Silva(1)
Affiliations : (1) Institut de Recerca en Energia de Catalunya (IREC), Sant Adrià del Besòs, Barcelona, Spain. (2) IN2UB, Departament d'Enginyeria Electrònica I Biomédica, Universitat de Barcelona, Barcelona, Spain.

Resume : State-of-the-art (semi-)transparent photovoltaics (TPV) are mainly focused on the partial absorption of visible light and/or multiple conversion mechanisms of UV or IR spectra. By selectively absorbing UV and NIR light the Shockley–Queisser limit for the efficiency of a single junction with 100% AVT is 20.6%. Turning the focus into the UV-selective harvesting, the field is still to be developed, showing promising results in the last couple years. Herein, we report on the synthesis of all-oxide transparent devices based on ZnO/NiO, using transparent conductive oxides as electrical contacts. NiO has been synthesized by thermal and e-beam evaporation and ZnO by DC-pulsed magnetron sputtering. Additionally, post-deposition annealing treatments and O3 treatments have been explored in order to improve the optoelectronic properties. Characterization by Raman, UV-VIS, XRD, SE and SEM have been done. Devices have been fabricated with thickness in the range of 10-50 nm for NiO and 100-400 nm for ZnO. We have obtained rectifying diodes that are sensitive to UV light and act as photodetectors. Ongoing experiments are being done with a UV-enhanced solar simulator to evaluate the PV functionality of these devices. Results of the best devices will be presented as well as a discussion on the need of a specialized solar simulator for PV characterization in this topic. This work has received funding from the European Union H2020 Framework Programme under Grant Agreement no. 826002 (Tech4Win).

Authors : C. Venugopalan Kartha*, G. Schmerber**, J.-L. Rehspringer**, D. Muller*, S. Roques*, A. Slaoui*, T.Fix*
Affiliations : *ICube Laboratory, Université de Strasbourg and CNRS, 23 rue du Loess, BP 20 CR, F-67037 Cedex 2 Strasbourg, France; **Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), Université de Strasbourg and CNRS, 23 rue du Loess, BP 43, F-67034 Cedex 2 Strasbourg, France

Resume : Cuprous oxide thin films are potential candidates for various optoelectronic devices. The Cu2O material has been up to now delivering the highest solar cell efficiencies among many oxides. In general, oxides can provide the advantages of abundance, stability, non-toxicity and low-cost manufacturing with a wide range of thin film deposition methods. Here we successfully prepared p-type Cu2O thin films by pulsed laser deposition. The growth conditions were carefully optimized to provide the best conductivity and mobility. The properties of these films were analyzed structurally, optically and electrically by different techniques. X-ray diffraction patterns of the films deposited on quartz substrates showed significant peaks for (200), (311), (220) and (111) indicating good crystallization. Approximately 250 nm thick cuprous oxide films were found to have resistivity of 60, a high mobility of 25 cm2/(V.s) and a bandgap of around 2 eV. We will describe the fabrication of all-oxide solar cells based on these films, their characterizations and optimization.

Authors : Abderrahime Sekkat* (1,2,3), Daniel Bellet (1), Anne Kaminski-Cachopo (2), Guy Chichignoud (3), David Muñoz-Rojas (1)
Affiliations : (1)Univ. Grenoble Alpes, CNRS, Grenoble INP, LMGP, 38000 Grenoble, France (2)Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, IMEP-LaHC, 38000 Grenoble, France (3)Univ. Grenoble Alpes, CNRS, Grenoble INP, SIMAP, 38000 Grenoble, France. *Lead presenter,

Resume : Cuprous oxide (Cu2O) is a non-toxic and abundant p-type semiconductor with a direct band gap around 2.1 eV and a large visible absorption coefficient. It has been studied and developed for several devices such as solar cells, thin film transistors or batteries. In this study, an innovative technique for depositing conformal and high-quality thin films, AP-SALD (Atmospheric Pressure Spatial Atomic Layer Deposition), is used to deposit Cu2O at low temperatures (up to 260 °C), under atmospheric pressure for photovoltaic applications. AP-SALD is an alternative approach to conventional ALD in which the precursors are separated in space rather than in time, allowing fast deposition rates as compared to conventional ALD (up to nm/s in some cases). The aim is to optimize the low-cost Cu2O deposition by AP-SALD on different substrates, even flexible, with a control over growth rate and transport properties (mobility and concentration of carriers). The effect of deposition parameters has been carefully studied, and mobility values of 91 cm²V-1s-1 have been obtained, close to values associated to epitaxial Cu2O thin films or Cu2O single crystals. Optimized Cu2O thin films, combined with n-type ZnO also deposited by AP-SALD, lead to all-oxide solar harvesters with efficiency rivaling values for similar devices made with high temperature and/or vacuum approaches. This shows that AP-SALD is a suitable approach to fabricate all-oxide solar harvesters, on both glass and flexible substrates.

Authors : Hajer Doghmen, Maria Zhukova, Jackson Lontchi and Denis Flandre
Affiliations : ICTEAM, UCLouvain, Place du Levant 3, 1348, Louvain-la-Neuve, Belgium

Resume : Our work investigates the structural, morphological, optical, and electrical properties of thin films of CuO deposited on soda-lime glass by spin-coating. The molar concentration of the precursor solutions, number of successive layers (from 1 to 3), drying time after the deposition of each layer (at 220°C in a furnace under air) and final annealing (at 550°C under oxygen for 1 hour), all appear crucial to achieve both light absorption and electrical conduction properties suitable for photovoltaic applications. The elementary compositions of the solutions are characterized by conductivity and ICP spectrometry. The films deposited from a 1 molar concentration solution, with a drying time of 15 min, features the better reproducibility of the measurements and the highest absorption coefficient (> 10^5 cm^(-1)). Structural analysis by XRD shows that all samples are polycrystalline with a monoclinic crystal structure. When we increase the number of layers, profilometer measurements show an increase of thickness about 160 nm per layer, SEM images show an increased average grain size, optical UV-Vis characterization shows a decrease in the transmission and an increase in the absorption coefficient. The optical band gap changes from 1.76 to 2.61 eV, while the carrier concentration and mobility (measured by Hall effect) vary respectively from 1.36 x 10^(15) to 5.84 x 10^(13) cm^(-3) and from 23.62 to 1.35 x 10^(3) cm^(2)/Vs.

Authors : Jihyun Kim(1), Hye Ri Jung(1), Yeon Soo Kim(1) and William Jo*(1)
Affiliations : (1)Department of physics in Ewha Womans University, Seoul 03760 Korea

Resume : TiO2 and SnO2 are popular metal oxide semiconductors (MOS) that are used for many applications due to their unique properties. This study reconstructs the importance of the combination of MOS as electron extraction layers for photovoltaic applications. Double metal oxide layer TiO2-SnO2 (DMOTS) can provide that, compared to their individual film, an improved optical and electrical properties. The morphological, physicochemical properties of the DMOTS was compared on the glass, FTO, ITO and SiO2/Si substrates. Surface facile photochemical treatment of DMOTS, such as UV–ozone (UVO) treatment, was applied to SnO2-TiO2 films deposited on the four substrates. Optical properties (PL and TRPL) showed to enhance the charge extraction and reduce charge recombination of DMOTS due to UV-sintering. Spectroscopic and microscopic techniques were conducted to investigate the physicochemical properties of the samples. The band structure, surface potential and carrier transport mechanism were explained by Kelvin probe force microscopy and ultraviolet photoelectron spectroscopy. Higher carrier concentration and lower resistivity of DMOTS was displayed by hall measurements when compared with TiO2. The results suggest that the DMOTS can serve as a better electron extraction layer to promote charge separation and suppress charge recombination. Therefore, these are beneficial for reducing the recombination of carriers, enhancing of perovskite solar cell performance.

12:30 LUNCH    
Oxide solar cells and TCO : Federico Rosei
Authors : Ming-Min Yang, Marin Alexe
Affiliations : Department of Physics, the University of Warwick

Resume : The symmetry lies at the heart of the law of nature and forms the basis for modern physics. Breaking of inversion symmetry by external stimuli would enable in certain materials exotic phenomena which are otherwise are prohibited. Here, we would like to introduce a new physical concept to harvest solar energy into electricity by inversion asymmetry engineering, i.e. the flexo-photovoltaic effect. The flexo-photovoltaic effect is the generalized version of the well-known bulk photovoltaic effect induced by the strain gradient. The strain gradient, namely inhomogeneous strains, induces electric polarization in materials of all symmetry and in the same time enables manifestation of the bulk photovoltaic without any symmetry limitation. The non-equilibrium charge separation mechanism therein is distinctive from the conventional photovoltaic effect based on built-in field (such as p-n junctions). Breaking the inversion symmetry induces an asymmetric distribution of the non-equilibrium photo-generated carriers in momentum space. This flex-o-photovoltaic effect not only that provides new insights into understanding the structure-property correlations in photo-active materials, but since it can be induced in the present solar cell technologies it might provide a route to boost the energy conversion efficiency of a wide pool of established semiconductors.

Authors : Hussain Muhammad1 Jung Jongwan1, Sajjad Hussain1,
Affiliations : 1 Graphene Research Institute, Sejong University, Seoul 143-747, Republic of Korea: Department of Nanotechnology & Advanced Materials Engineering and Graphene Research Institute, Sejong University, Seoul 143-747, Republic of Korea

Resume : Abstract: We have fabricated a heterojunction for wavelength selective photoconductivity based on n-IGZO material (bandgap 3.1 eV) [1] for UV and visible absorption and p-GeSe material (bandgap 1.1 eV) [2] for NIR photon absorption. The device exhibits photoresponse without external bias voltage under NIR light illumination (wavelength ~850 nm), UV light (wavelength ~360 nm) and visible photon (wavelength ~ 530 nm). The I-V characteristics of the device explicitly show the variation of the open-circuit voltage for dark (0 V), visible (0.28 V), UV (0.4 V) and NIR (-0.29 V). The time-dependent photoresponses of the device were carried out at zero bias under laser irradiation UV, visible and NIR, the photocurrent values corresponding to light on a state for UV and visible light were noticeably negative while for NIR light on the state were obviously positive. The rise time (τr time taken by device to reach 90% from 10%) and fall time (τf, time is taken by device to decay from 90% to 10%) [3] were examined, rise and fall time corresponding to under illumination of NIR of 0.32s and 0.34s respectively. This sensitivity changes under the wavelength of the selected light conditions, the effect is strictly depending on optical absorption properties and band gap of the material. The photogenerated by polarity flipping is useful for promising selective photodetection. References: [1]Yu, Jingjing, et al. "High-Performance Visible-Blind Ultraviolet Photodetector Based on IGZO TFT Coupled with p–n Heterojunction." ACS applied materials & interfaces 10.9 (2018): 8102-8109. [2] Liu S-C et al 2017 Investigation of physical and electronic properties of GeSe for photovoltaic applications Adv.Electron Mater.31700141 [3] Xie, C.; Yan, F. Flexible Photodetectors Based on Novel Functional Materials. Small 2017, 13, 1701822.

Authors : D. Bellet1, D.T. Papanastasiou1, L. Bardet1,2, C. Jiménez1, D. Muñoz-Rojas1
Affiliations : 1 Univ. Grenoble Alpes, CNRS, Grenoble INP, LMGP, 38000 Grenoble, France ( 2 Univ. Grenoble Alpes, CNRS, Grenoble INP, LGP2, 38000 Grenoble, France

Resume : Transparent conducting materials (TCM) that are used as transparent electrodes in solar cells constitute a key component. The currently used TCM are indium tin oxide (ITO) or other transparent conducting oxides, TCO, such as aluminium-doped zinc oxide (AZO), or fluor-doped tin oxide (FTO). However indium scarcity and the lack of flexibility of TCO in general have prompted the search for alternative low cost and flexible TCM which can exhibit promising properties (such as transparency in the NIR) while containing no critical raw materials. The main properties concern not only the optical transparency, the sheet resistance but also the haziness for instance, or the roughness of the layers. There has been lately a growing interest for several material technologies. For instance metallic nanowire networks and metallic grids appear promising since they exhibit high optical transparency, very good electrical properties and mechanical flexibility; while they show promising integration results. Conductive polymers and carbon based TCM (graphene or carbon nanotubes), can also be potentially interesting. The association between these different TCM technologies is currently the subject of intensive research with the aim of optimizing these nanocomposites. Finally we will describe what appear to be the future most promising and innovative research directions in the field of emerging TCM for integration into solar cells, as well with the main associated future challenges.

Authors : Diana Dahliah, Gian-Marco Rignanese, and Geoffroy Hautier
Affiliations : Institute of Condensed Matter and Nanoscience (IMCN), Université catholique de Louvain (UCLouvain), Chemin étoiles 8, bte L7.03.01, Louvain-la-Neuve 1348, Belgium, Institute of Condensed Matter and Nanoscience (IMCN), Université catholique de Louvain (UCLouvain), Chemin étoiles 8, bte L7.03.01, Louvain-la-Neuve 1348, Belgium, Institute of Condensed Matter and Nanoscience (IMCN), Université catholique de Louvain (UCLouvain), Chemin étoiles 8, bte L7.03.01, Louvain-la-Neuve 1348, Belgium

Resume : Transparent Conducting Oxides TCOs, combine a wide bandgap with good conductivity properties, such an unusual combination can be obtained by doping (n-type or p-type) a wide band gap oxide. These material have critical role in industrial applications such as sensors, touchscreens, solar cells.. etc. p-type conductors are lagging behind in their performance because of the low hole mobility due to the presence of localized O 2p orbitals in the valence band. Breaking this localization and finding a p-type material with good conductivity as the one of n-type TCOs will make a revolution in the industry and will flip the type of materials that are used in some industrial applications such as solar cells. In a recent paper, Ba2BiTaO6 was reported as remarkable high mobility p-type TCOs though its conductivity is limited by charge compensation[1]. Here, we used first-principles computations to investigate the reasons behind such a low conductivity from a defects physics standpoint. The calculated defect formation energies confirm that K is an adequate p-type shallow extrinsic dopant but that high p-type doping is prevented by the presence of compensating defects. Our work stresses the inherent difficulty in doping Ba2BiTaO6 , we also highlight the potential directions for future improvements in its conductivity. [1] A. Bhatia et al., Chem. Mater. 28, 30-34 (2016)

Hybrid perovskites (II) : Marin Alexe
Authors : Jan Christoph Goldschmidt, Alexander J. Bett, Patricia S. C. Schulze, Kristina M. Winkler, Özde Kabakli, Martin Bivour, Ludmila Cojocaru, Sebastian Nold, Leonard Tutsch, Lukas Wagner, Martin Hermle, Stefan W. Glunz
Affiliations : Fraunhofer Institute for Solar Energy Systems

Resume : To enable terawatt-scale photovoltaics, resource and cost efficiency are mandatory. Perovskite silicon tandem solar cells can achieve both goals, by exceeding the efficiency limit of 29.4% of single junction silicon solar cells, with only little added production costs. For highest efficiencies, important material-related choices concern the absorber material, the contacting and passivation layers, and the sequence of deposition. We apply a photo-stable mixed cation mixed halide perovskite FA0.75Cs0.25Pb(I0.8Br0.2)3 absorber with a bandgap of 1.7 eV, in the optimal range for monolithic silicon-based tandem devices. This absorber is used in both n-i-p and p-i-n devices. In the n-i-p-configuration, an n-type silicon heterojunction (SHJ) bottom solar cell is connected via an ITO recombination contact to the perovskite top solar cell. Evaporated compact TiO2 and UV-treated mesoporous TiO2 form the electron contact, passivated with spin-coated PCBM and PMMA. The hole contact is formed by evaporated Spiro-TTB and directly sputtered ITO, capped with an evaporated MgF2 antireflection coating (ARC). This configuration reaches 23.4% stabilized efficiency. In the p-i-n-configuration, a p-type SHJ solar cell with an ITO recombination contact is coated with spincoated PTAA and PFN, the perovskite absorber, evaporated C60, ALD-deposited SnOx, sputtered ITO and again MgF2 ARC. Despite a lower voltage, this configuration achieves 24.5% stabilized efficiency due to a higher current.

Authors : Hannah-Noa Barad, Eran Oren, Mariana Alarcon-Correa, and Peer Fischer
Affiliations : Max Planck Institute for Intelligent Systems, Heisenbergstr. 3, 70569 Stuttgart, Germany

Resume : Combinatorial materials science (CMS) is a promising method for fast discovery of new functional materials. CMS has been used to form thin films with composition and thickness gradients, thus, synthesizing on a single substrate a range of samples with systematically varying properties, which is a first step in finding new materials and device structures. Apart from the composition or thickness, film morphology can be especially important for an assortment of applications, especially in photovoltaics, as morphology governs the chemical reactivity, determines the surface area, and is important for charge mobility and recombination processes. However, to date CMS has mostly ignored film morphology as a study parameter. Here we describe how to vary morphology and material composition at the same time using an adapted shadow growth method based on glancing angle deposition (GLAD). In a one-step, well-controlled growth we quickly obtain a large number of nano columnar structures, including rods, helices, and zigzags with varying material compositions. GLAD also eliminates the commonly used wet chemical steps for nanostructure synthesis. Adapting GLAD for CMS, with accompanying high-throughput characterization, constitutes an integrated approach for discovering new materials and structures for a multitude of applications in many scientific fields. We use this method to fabricate a multi-component composite photovoltaic absorber and study the compositional and structural variations.

Authors : Hin-Lap Yip
Affiliations : South China University of Technology

Resume : Over the past few years, organic-inorganic hybrid perovskites have emerged as a new class of solution processable semiconductor for many optoelectronic applications, such as solar cells and light emitting devices (LEDs). Their electronic, electrical and optical properties can be controlled by tuning their compositions and crystal structures. In this talk, I will discuss how to lean on the experience in interface engineering for organic solar cells and design new electron[1-3] and hole[4-5] transport conjugated materials with proper interfacial properties to improve the charge collection efficiency of perovskite solar cells. In the second part, I will also discuss how to control the dimension and nanostructure of perovskites by introducing small molecules and polymers with tailored functional groups that can strongly interact with the perovskite crystals. Using such strategy, we have developed very stable Sn-based low bandgap perovskite solar cells with much improved stability and efficiency[6] as well as highly efficient red[7] and blue[8,9] emitting perovskite LEDs. Reference: (1) S. Chen, H.-L. Yip, M. Wang, F. Huang, et al, Adv. Energy Mater., 2016, 6, 1501534. (2) L. Yan, Q. Xue, H.-L. Yip, et al, Adv. Mater. 2018, 30, 1802509 (3) J. Tian, Q. Xue, H.-L. Yip, et al, Adv. Mater. 2019, 31, 1901152 (4) Q. Xue, B. Zhang, H.-L. Yip, et al, Adv. Energy Mater., 2016, 6, 1502021. (5) Q. Xue, Y. Li, H.-L. Yip, et al, Adv. Funct. Mater., 2018, 28, 1707444 (6) Z. Chen, H.-L. Yip, et al, iScience 2018, 9, 337-346. (7) W. Cai, H.-L. Yip, et al. ACS Appl. Mater. Interfaces 2018, 10, 42564-42572. (8) Z. Chen, H.-L. Yip, et al Adv. Mater. 2017, 29, 1603157. (9) Z. Li, H.-L. Yip, et al Nat. Commun. 2019, 10, 1027

16:00 Break    
Authors : Marie Legrand * (1)(2), Adrien Bercegol (1)(2), Laurent Lombez (1)(4), Jean-François Guillemoles (2)(3), Daniel Ory (1,2)
Affiliations : (1) EDF R&D, France (2) Institut Photovoltaïque d’Ile de France (IPVF), France (3) CNRS, Ecole Polytechnique, UMR IPVF, France (4) Laboratoire de Physique et Chimie des Nano-objets, France

Resume : Analyzing the photoluminescence (PL) of semiconductors complementarily in time and wavelength allows to derive their key optoelectronic and transport properties. Up to now, separate acquisitions have to be performed. We developed a 4D imaging set-up that allows the acquisition of spectral and temporal luminescence intensity with micrometric spatial resolution. Very notably, this dataset is acquired simultaneously and hence with exact same experimental conditions. This novel set-up relies on single pixel imaging technology, an approach that enables the reconstruction of the spatial information recorded from a higher resolution non-imaging detector. The sample PL signal is spatially modulated with different patterns by a digital micro-mirror device1. We make use of this technique for the first time with a streak camera as a detector, allowing to record the PL intensity decays and spectrum for each pixel with very high temporal (<100ps) and spectral resolutions (< 1nm). A patent application has been filled. We already performed successful measurements and 4D numerical reconstructions and we demonstrate the use of this setup by characterizing hybrid mixed halide perovskite samples. We extract and analyze the material properties (gap) at different time scales as well as the carrier recombination (lifetime, radiative coefficient) and transport (diffusion coefficient) properties with a single experiment. 1 Duarte et al, IEEE Signal Process. Mag. 25, 83 (2008).

Authors : B. Traore, L. Pedesseau, J.-C. Blancon, S. Tretiak, A.D. Mohite, J. Even, C. Katan, M. Kepenekian
Affiliations : Univ Rennes, INSA Rennes, CNRS, Institut FOTON - UMR 6082, F-35000 Rennes, France; Univ Rennes, ENSCR, INSA Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes) - UMR 6226, F-35000 Rennes, France; Department of Chemical and Biomolecular Engineering, Rice University, Houston, TX 77005; Los Alamos National Laboratory, Los Alamos, NM 87545, USA

Resume : The spectacular rise of the photovoltaic power conversion efficiency of hybrid organic-inorganic perovskites to over 25% in just a decade has conferred them a promising position in the field of photovoltaics1. This has urged an extensive worldwide research interest in solar energy solutions based on the so-called MAPbI3 (MA = CH3NH3) material and its mixed cations/anions variants. The excellent photovoltaic performance of MAPbI3 is partly attributed to its interfacial properties with the proper choice of charge selective layers and doping/alloying. Among the possible contact materials, nickel oxide (NiO) is commonly used as a hole transporting layer in thin-film optoelectronic technologies based on organic or hybrid materials. Here, we computationally scrutinize the interfacial properties of the prototype MAPbI3/NiO heterostructure, which has shown excellent photovoltaic performance and in particular a large open-circuit voltage2,3. We study the valence band energy level alignment between MAPbI3 and NiO considering i) the defect-free system ii) the role of defects and iii) doping. We show that the defect-free ideal NiO interface with MAPbI3 is not in favor of enhanced hole collection and largely points to a valence band offset that seemingly contradicts the experimentally reported values. Our results indicate that the presence of native Ni-vacancies in deposited NiO is at the origin of near ideal valence band energy level alignment between MAPbI3 and NiO. We further demonstrate the improvement of hole transport across the interface due to NiO doping with Li. Our Subsequently, we propose alternative dopants. Our results suggest the high tunability of NiO interfaces for the design of optimized optoelectronic devices. More, the developed methodology is suitable to inspect the properties of other interfaces4 and devices far beyond halide perovskites. References 1., Accessed: 10-01-2020. 2. Traore et al., “Importance of Vacancies and Doping in Hole Transporting Nickel Oxide Interface with Halide Perovskites”, ACS Appl. Mater. Interfaces, 2019, in press 3. Nie et al., “Critical Role of Interface and Crystallinity on the Performance and Photostability of Perovskite Solar Cell on Nickel Oxide”, Adv. Mater., 30, 1703879, 2018 4. Devesa et al., “Halide Perovskite High-k Field Effect Transistors with Dynamically Reconfigurable Ambipolarity”, ACS Materials Lett., 1, 633-640, 2019

Authors : Robert A. Jagt1, Tahmida N. Huq1, Sam A. Hill1, Maung Thway3, Tianyuan Liu3, Mari Napari1,2, Bart Roose4, Krzysztof Gałkowsk4, Weiwei Li1, Serena Fen Lin3, Samuel D. Stranks4,5, Judith L. MacManus-Driscoll1, Robert L. Z. Hoye1,6,*
Affiliations : 1 Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, UK 2 Present address: Zepler Institute for Photonics and Nanoelectronics, University of Southampton, University Road, Southampton SO17 1BJ, UK 3 Solar Energy Research Institute of Singapore, National University of Singapore, Singapore 117574 4 Department of Physics, Cavendish Laboratory, University of Cambridge, 19 JJ Thomson Avenue, Cambridge CB3 0HE, UK 5 Department of Chemical Engineering and Biotechnology, University of Cambridge, Philippa Fawcett Drive, Cambridge CB3 0AS, UK 6 Present address: Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ, UK

Resume : Perovskite solar cells (PSCs) with transparent electrodes can be integrated with existing solar panels in tandem configurations to increase the power conversion efficiency. A critical layer in semi-transparent PSCs is the inorganic buffer layer, which protects the PSC against damage when the transparent electrode is sputtered on top. The development of n-i-p structured semi-transparent PSCs has been hampered by the lack of suitable p-type buffer layers. In this presentation we develop a p-type CuOx buffer layer, which can be grown uniformly over the perovskite device without damaging the perovskite or organic charge transport layers, can be grown using industrial scalable techniques and has high hole mobility (4.3 ± 2 cm2 V-1 s-1), high transmittance (>95%), and a suitable valance band maximum for hole extraction (5.3 ± 0.2 eV). Semi-transparent PSCs with efficiencies up to 16.7% are achieved using the CuOx buffer layer. Our work provides a new approach to integrate the most efficient architecture for PSCs for tandems, as well as other applications requiring semi-transparent devices, such as bias-free solar fuel production, transistors with transparent electrodes, and spectroscopy on devices under operation.

Authors : Sirazul Haque*, Miguel Alexandre, Manuel J. Mendes, Hugo Águas, Elvira Fortunato, Rodrigo Martins *Corresponding author:
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 : Optical strategies create a conducive path for perovskite solar cell (PSC) technology development, not only to increase their efficiency, but also to enable less material usage - in view of enhanced flexibility and improve the cells´ stability [1-2]. We developed and studied two novel photonic concepts in the wave-optics regime and applied them to PSCs with distinct thicknesses of the perovskite absorber (250-500 nm). First, front-located photonic-structured electron transport layers (ETLs) demonstrated the best photocurrent improvement (up to 27% - value rather close to the fundamental Lambertian limit), together with a proclivity to protect the absorber layer from harmful UV radiation which is a vital issue concerning the PSCs stability. Secondly, PSCs conformally deposited on photonic-structured substrates show also a comparable photocurrent enhancement to the previous structure (up to 25%). Furthermore, this latter configuration also offers considerable practical advantages regarding its applicability in the PSCs’ process technology. Moreover, optimal wavelength-sized semi-spheroidal structured substrates also show a significant omni-directional optical response for angles up to 70º, therefore underlining the viability of this light trapping scheme for implementation in flexible photovoltaic (PV) devices that need optimal operation under bending. In addition, both photonic-embedded ultra-thin solar cells designed here ultimately support the reduction of material usage in PSC technology, that positively accommodates the reduction of the absorber thickness to more than 2-fold, thereby improving the intrinsic mechanical flexibility, as well as the mitigation of lead usage, without impacting the device’s performance. References: [1] S. Haque et al. Nano Energy. 59 (2019) 91–101 and [2] S. Haque et al. Optica under publication (2020)

Authors : Chih-Wei Chu, Mriganka Singh
Affiliations : Chih-Wei Chu and Mriganka Singh: Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan

Resume : Metal oxide charge carriers transporting materials have been explored in numerous ways to fabricate perovskite solar cells (PSCs) due to its excellent chemical stability, wide bandgap, high mobility as well as low-cost. In this study, we report a low-temperature solution-processed facile intercalation method to allow metal oxide to behave bipolar transporting capability for optoelectronic applications. A p-type nickel oxide (NiO) surface-intercalated with n-type cesium carbonate (Cs2CO3) was used as hole and electron transport layers applicable in both inverted (p-i-n) and planar (n-i-p) type of PSCs. As a result, the champion power conversion efficiency for the inverted and planar-based PSCs has been reached up to 12.08, and 13.98%, respectively, which indicated that this type low-temperature solution-processed metal oxide is very promising for optoelectronics applications especially used as an interconnecting layer in tandem photovoltaics.

Authors : Julie Roger* (1), Raphael Schmager (1), Jonas A. Schwenzer (2), Fabian Schackmar (2), Tobias Abzieher (2), Mahdi Malekshahi Byranvand (1), Bahram Abdollahi Nejand (1), Paul Faßl (1), Matthias Worgull (1), Bryce S. Richards (1,2) and Ulrich W. Paetzold (1,2)
Affiliations : 1: Institute of Microstructure Technology (IMT), Karlsruhe Institute of Technology (KIT), 76344 Karlsruhe, Germany 2: Light Technology Institute (LTI), Karlsruhe Institute of Technology (KIT), 76128 Karlsruhe, Germany

Resume : The power conversion efficiency (PCE) of perovskite solar cells (PSC) has increased impressively within the last years and exceeds 25% today. A remaining challenge is the limited stability of PSC. Previous work indicated that inorganic charge transport layers (CTL) can help to improve the stability. However, the choice of materials is limited due to the employed layer-by-layer deposition, since each layer deposition must preserve the already processed layer stack, e.g. from dissolving. In order to overcome this limitation, we present a novel lamination approach: the hot pressing of two independently processed half-stacks of the PSC [1]. The separation of the CTL deposition enables new material combinations, in particular full oxide contact materials with enhanced stability. To allow this architecture, a certain importance must be set on the adhesion of the half stacks which is shown to be improved by additional buffer layers. We demonstrate stable power outputs as high as 14.6% PCE with high stability during continuous maximal power point tracking over 90 h. Even at temperatures up to 80 °C or realistic temperature profiles, the champion device exhibits good thermal stability during prolonged illumination. Furthermore, flexible and semi-transparent PSC are successfully laminated, demonstrating the high versatility of the process in particular for future applications in the field of tandem photovoltaics. [1] R. Schmager, J. Roger et al., Adv. Funct. Mat., 2020, in press.

Authors : S.Sahayaraj1,, Eros Radichi2,3, Marcin Ziolek4, Jarosław Serafińczuk5 and Konrad Wojciechowski1,6
Affiliations : 1Saule Research Institute (SRI), division of Saule Technologies, 11 Dunska, 54-130, Wroclaw, Poland, 2Department of Chemistry, Biology and Biotechnology, University of Perugia, via Elce di Sotto 8, 06123 Perugia, Italy 3 Computational Laboratory for Hybrid/Organic Photovoltaics (CLHYO), CNR-ISTM, via Elce di Sotto 8, 06123 Perugia, Italy. 4Faculty of Physics, Adam Mickiewicz University in Poznan, Umultowska 85, 61-614 Poznan ,Poland. 5Faculty of Microsystem Electronics and Photonics, ul. Janiszewskiego 11/17, Wroclaw University of Science and Technology, Poland. 6 Saule Technologies, 11 Dunska, 54-130, Wroclaw, Poland

Resume : An emerging variant of metal halide perovskites, the 2D perovskites are gaining popularity due to their excellent stability. This arises due to the presence of bulky organic spacer cations which can block moisture and offer spatial confinement to the diffusion of ions through the inorganic [PbI6]4- octahedral network. This feature comes with a price as the bulky cations result in reduced and anisotropic charge transport in solar cells made of 2D perovskites, making them less efficient than their 3D counterparts. Standard formulation developed in our lab involves Phenyl Ethyl Ammonium Iodide (PEAI) as large cation, Methyl ammonium iodide and Lead Iodide in a 2:4:5 molar ratio forming the perovskite layer (n = 5), together with the use of coordinating additives like NH4SCN (TC). This formulation gives us devices in the efficiency range 9 -11% with low hysteresis. However, short circuit current density (Jsc) in the range of 11 – 12 mA/cm2 and Fill factor (FF) in the range 65% – 70% strongly indicate problems related to charge carrier transport across the solar cell. To achieve seamless carrier transport in 2D perovskites a perfect vertical orientation of the [PbI6]4- octahedral cages with respect to the electrodes is desired. We engineered the additive, by replacing TC with Thiosemicarbazide (TSC), due to its high coordination strength to lead, coming from the S-donor (which acts as a strong Lewis base). We replaced PEAI with 4F-PEAI (fluorine atom substituted at the para position of the phenyl ring), due to enhanced orbital interactions between inorganic layers. Both replacements are expected to help in templating preferred orientation of the perovskite sheets. The resulting solar cells outperformed our standard devices with 25% higher gains in efficiency. The Jsc is in the range 14.8 – 16.4 mA/cm2, to go with a FF of 73% -78%, a significant leap from our standard devices. Transient Absorption Spectroscopy (TAS) revealed a coexistence of 2D and 3D perovskite phases with a higher contribution of 2D phases (n = 2,3,4) close to the substrate and a higher contribution of the 3D phase (n = ꝏ) close to the surface. The non-encapsulated solar cells show excellent storage efficiencies for several months and also very stable performance under accelerated test conditions for 400 hours. These results can be attributed to the specific combination of both the large cation and the additive.

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09:45 Break    
Novel photovoltaic absorbers (I) : Reuben Collins
Authors : Judith MacManus-Driscoll1, Tahmida N. Huq1, Robert A. Jagt1, Robert L.Z. Hoye2
Affiliations : 1. Department of Materials Science and Metallurgy, University of Cambridge, Cambridge 2. Department of Materials, Imperial College London, South Kensington, London

Resume : Bismuth-based compound have recently gained increasing attention as air-stable, defect tolerant and non-toxic alternatives to lead-halide perovskites. We are interested in highly stable Bi-based inorganic compounds. Bismuth oxyiodide (BiOI) with an electronic structure replicating that of lead halide perovskites, has emerged as a promising contender. It is predicted to show tolerance towards anti-site and vacancy defects. Notably, BiOI thin films have been found to be at least two orders of magnitude more air-stable than methylammonium lead iodide. We experimentally investigate the tolerance of BiOI to Bi, I and O vacancy and anti-site defects by vacuum annealing BiOI films at low temperature 100°C under vacuum. Despite large defect concentrations, the electronic and optoelectronic properties of BiOI remain unaltered which experimentally validates the calculations and proves the defect tolerance of the phase and robustness of the compound. Furthermore, through single crystal growth experiments, we show the relation between carrier lifetimes and the nature of the defects.

Authors : Tahmida N. Huq (1), Lana C. Lee (1), Lissa Eyre (2), Weiwei Li (1), Robert A. Jagt (1), Chaewon Kim (3), Sarah Fearn (4), Vincenzo Pecunia (3), Felix Deschler (2), Judith L. MacManus-Driscoll (1) and Robert L. Z. Hoye (4)
Affiliations : 1. Department of Materials Science and Metallurgy, University of Cambridge, Cambridge 2. Walter Schottky Institute, Technical University of Munich, Germany 3. Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University, P. R. China 4. Department of Materials, Imperial College London, South Kensington, London

Resume : Bismuth oxyiodide (BiOI) has emerged as a promising contender amongst non-toxic alternatives to lead-halide perovskites. This is due to BiOI demonstrating air-stability over 3 months and compelling early-stage photovoltaic performance. Notably, BiOI is predicted from calculations to tolerate vacancy and anti-site defects. In this work, we experimentally investigate the tolerance of BiOI to point defects. BiOI thin films are annealed at a low temperature of 100 °C under vacuum. We observe a relative reduction in the surface atomic fraction of iodine by over 40%, reduction in the surface bismuth fraction by over 5%, and an increase in the surface oxygen fraction by over 45%. Remarkably, the Bi 4f7/2 core level position, Fermi level position and valence band density of states of BiOI are not significantly changed, nor are the charge-carrier lifetimes and photovoltaic performance. Our data demonstrates BiOI to be electronically and optoelectronically robust to percent-level changes in surface composition. However, from photo-induced current transient spectroscopy measurements, we find that the as-grown BiOI films have deep traps located approximately 0.3 to 0.6 eV from the band-edge. These are three-four orders of magnitude lower in concentration than the defects we induce through vacuum annealing and have a different origin. Future improvements in the performance of BiOI photovoltaics will need to focus on identifying how these arise. Nevertheless, our work shows BiOI to be robust against processing conditions that lead to percent-level iodine-, bismuth- and oxygen-related surface defects which is crucial for reductions in the cost of fabricating BiOI-based electronic devices.

Authors : A. Shongalova, S. Ranjbarrizi, S. Garud, B. Vermang, J.M.V. Cunha, K. Lorenz, P.M.P. Salomé, M.R. Correia, P.A. Fernandes
Affiliations : A. Shongalova (a,b), S. Ranjbarrizi (c), S. Garud (c), B. Vermang (c), J.M.V. Cunha (b,f), K. Lorenz (e), P.M.P. Salomé (f), M.R. Correia (b), P.A. Fernandes (b,d,f,∗) (a) Satbayev University, Satpayev street, 22a, 050013 Almaty City, Kazakhstan (b) I3N / Departamento de Física, Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal (c) IMEC, Kapeldreef 75, 3001 Leuven, Belgium. (d) CIETI / Departamento de Física, Instituto Superior de Engenharia do Porto, Instituto Politécnico do Porto, Rua Dr. António Bernardino de Almeida, 431, 4200-072 Porto, Portugal (e) INESC-MN, IPFN, Instituto Superior Técnico (IST), Campus Tecnológico e Nuclear, Estrada Nacional 10, km 139.7, 2695-066 Bobadela LRS, Portugal (f) INL - International Iberian Nanotechnology Laboratory, Av. Mestre José Veiga 4715-330 Braga Portugal

Resume : In recent years, the scientific community has emphasized materials with a 2D structure. These types of materials have been designed for various application areas, with photovoltaic energy production being one of them. The Sb2Se3 semiconductor falls into this family and preliminary studies have shown that it presents optical and electrical properties compatible with photovoltaic technology. In this work we describe a method that allows the growth of Sb2Se3 which is easily up scalable for industrial environment. The method consists of the Sb-Se precursor films deposition using RF magnetron sputtering and a subsequent annealing step in an H2Se atmosphere. The physical properties of the samples are studied using several techniques, such as scanning electron microscopy, energy dispersive spectroscopy, x-ray diffraction Rutherford Backscattering Spectrometry, and Raman, allowing to access the material structure, composition and morphology. The effect of the substrates, such as Si, Mo and soda lime glass in the Sb2Se3 growth and in the interface between the substrate and Sb2Se3 is also investigated. The optical characterization was also performed to extract the absorption coefficient and band gap energy.

Authors : Bruno Lorenzi1, Yoichiro Tsurimaki2, Akihiro Kobayashi3, Masayuki Takashiri3, Svetlana Boriskina2
Affiliations : 1 Department of Materials Science, University of Milano Bicocca. Milan – Italy 2 Mechanical Engineering Department, Massachusetts Institute of Technology, Cambridge, Massachusetts - USA 3 Department of Materials Science, Tokai University, Kitakaname - Japan

Resume : The need of a p-n architecture, and the scarcity of cheap small energy gap semiconductors, are usually reported as the main limitations for a wider diffusion of infrared (IR) detectors and harvesters. This lack of cheap IR photodiodes is often reported has a technological bottleneck for the internet of things. Bulk photovoltaic (PV) effect, based on photo-thermoelectricity and flexoelectricity are possible solutions to open the route to new materials and systems able to overcome these limitations. In this communication we present the experimental demonstration of IR photo-thermoelectric effect, enhanced by flexoelectricity in Bi2Te3 thin films. Depositing Bi2Te3 on flexible substrates, and developing ohmic contacts and anti-reflective coating by e-beam evaporation, we were able to analyze the system electrical response under strain gradient. We will show how the power output in our samples can be varied as a function of the applied strain, sample temperature, and illumination level at different wavelengths. Our results help to shed light on the relation between applied strain, material polarization, and the photon detector performance, and reveal new possible applications of bulk-PV effects in low-gap materials.

Authors : Zhenyu Wang, Joachim Breternitz, Susan Schorr
Affiliations : Zhenyu Wang 1 Helmholtz-Zentrum Berlin für Materialien und Energie, Structure and Dynamics of Energy Materials, Hahn-Meitner-Platz 1, 14109 Berlin, Germany 2 Freie Universität Berlin, Department Geosciences, Malteserstraße 74-100, 12249 Berlin, Germany; Joachim Breternitz 1 Helmholtz-Zentrum Berlin für Materialien und Energie, Structure and Dynamics of Energy Materials, Hahn-Meitner-Platz 1, 14109 Berlin, Germany; Susan Schorr 1 Helmholtz-Zentrum Berlin für Materialien und Energie, Structure and Dynamics of Energy Materials, Hahn-Meitner-Platz 1, 14109 Berlin, Germany 2 Freie Universität Berlin, Department Geosciences, Malteserstraße 74-100, 12249 Berlin, Germany

Resume : Growing concern over resource availability and toxicity are leading to a paradigm shift towards truly sustainable materials for photovoltaics. Zn-group IV-nitrides are one potential class of materials fulfilling these criteria, which adopt a wurtzite-type derived structure. The ternary nitrides were postulated to allow a unique bandgap tuning mechanism through cation disorder [1] in addition to cation alloying. Fully ordered structure ZnGeN2 crystallises in a ß-NaFeO2 type structure in a subgroup of the wurtzite type. Interestingly, incorporating oxygen into ZnGeN2 also introduces an increased degree of disorder in the material. [2] We present a detailed study of the degree of cation disorder in oxygen containing Zn1+xGeN2Ox that is revealed through neutron powder diffraction. Studying samples with a variable degree of oxygen allows us to conclude on the role of oxygen and further comparing different samples of nominally similar composition allows to decorrelate the oxygen effect from intrinsic cation disorder. We will combine our results with optoelectronic and chemical properties of the materials and finally aim to answer the question, whether cation disorder exists independently of oxygen incorporation or is fundamentally linked to it. [1] A.D. Martinez, A.N. Fioretti, E.S. Toberer, A.C. Tamboli, J. Mater. Chem. A, 2017, 5, 11418. [2] J. Breternitz, Z.Y. Wang, A. Glibo, A. Franz, M. Tovar, S. Berendts, M. Lerch, S. Schorr, Phys. Status Solidi A, 2019, 1800885.

Authors : F. Alnjiman(1.2), A. Almoshawah(3), A. Alodhyayb(2), S. Diliberto(1), H. Kabbaraa, S. Bruyère(1), J. Ghanbaja(1), , P. Boulet(1), H. Albrithin(1), J.F. Pierson(1)
Affiliations : (1)Institut Jean Lamour (UMR CNRS 7198), Université de Lorraine, Nancy, France; (2)Department of Physics and Astronomy at College of Science, King Saud University at Riyadh, Saudi Arabia; (3)Department of Physics College of Science, Shaqra University at Shaqra, Saudi Arabia

Resume : Zinc tin nitride (ZnSnN2) is a new semiconductor material with earth-abundant elements and low-cost production. It has a tunable direct band gap (1.0–2.2 eV) that may be due to cation disorder [1]. The band gap also can be tuned by changing the atomic ratio between Zn and Mg [2]. It has recently attracted considerable interest for solar energy applications and high speed electronics to replace the III-V materials historically used in optoelectronics. However, few works have been devoted to MgSnN2 [2,3]. This work presents the results of growth of ZnxMg1-xSnN2 thin films by reactive co-sputtering using zinc, magnesium and tin metallic targets. The stoichiometry of the films was controlled by optimizing operating parameters such as the target current and power. By changing the stoichiometry the morphology and the texture of the films can be tuned. We grew ZnSnN2 thin films with different stoichiometries. The structure of the films was studied by X-ray diffraction and the morphology by scanning electron microscopy. The microstructure was observed by transmission electron microscopy. More detailed information about the chemical environment of tin atoms has been obtained using 119Sn conversion electron Mössbauer spectroscopy. The optical band gap has been deduced from UV-Visible spectroscopy and ellipsometry measurements. The electrical resistivity and free-electron concentration was studied by Hall-effect measurement at room temperature. References [1] A. N. Fioretti, et al. « Effects of low temperature annealing on the transport properties of zinc tin nitride », in 2015 IEEE 42nd Photovoltaic Specialist Conference (PVSC), 2015, p. 1‑5, doi: 10.1109/PVSC.2015.7355694. [2] R. A. Makin et al., « Alloy-Free Band Gap Tuning across the Visible Spectrum », Phys. Rev. Lett., vol. 122, no 25, p. 256403, juin 2019, doi: 10.1103/PhysRevLett.122.256403. [3] F. Kawamura, et al., « Synthesis of a Novel Rocksalt-Type Ternary Nitride Semiconductor MgSnN2 Using the Metathesis Reaction Under High Pressure », Eur. J. Inorg. Chem., vol. n/a, no n/a, doi: 10.1002/ejic.201901059.

Authors : Elias Z. Stutz(1), Léa Buswell(1), Julien Gay(1), Mahdi Zamani(1), Jean-Baptiste Leran(1), Simon Escobar Steinvall(1), Nicolas Tappy(1), Rajrupa Paul(1), Anna Fontcuberta i Morral(1,2)
Affiliations : (1) Laboratory of Semiconductor Materials, Institute of Materials, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland; (2) Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland

Resume : The rapid development of the photovoltaic and optoelectronic industries and rising demand for cheap and efficient products are straining the supply of rare elements often required for the fabrication of the most cost-effective devices. Zinc phosphide (Zn3P2) solar cells are promising earth-abundant alternatives and could lead to widespread deployment of sustainable thin-film solar technology. The 1.5 eV direct bandgap of this semiconductor, close to optimal for photovoltaics, makes it a strong contender for this application. The micrometer-range minority carrier diffusion lengths [1] and the strong visible light absorption in the phosphide material further justify its investigation. Despite knowing the direct bandgap energy of our material with good accuracy, there remains a lot of controversy regarding the details of its band and defect structure. An indirect bandgap smaller than the direct bandgap is sometimes measured [1], but not predicted by ab initio calculations [2]. In this work, we shed light on the optical and electronic properties of zinc phosphide mono- and polycrystalline thin films grown by molecular beam epitaxy on indium phosphide. Using steady-state photoluminescence (PL), time-resolved PL and cathodoluminescence (CL), we have identified the different emissions and studied the effects of sample size and crystallinity. Additionally, we determined the optical properties of monocrystalline thin films using ellipsometry, with a robust first model for the material. Finally, we used CL to measure the diffusion length of the carriers in thin films. [1] G. M. Kimball, et al., Appl. Phys. Lett., 95(11), 112103 (2009) [2] J. Andrzejewski and J. Misiewicz, Phys. Status Solidi B, 227(2), 515-540 (2001)

12:30 LUNCH    
Novel concepts in traditional absorbers : Judith Driscoll
Authors : Neil S. Beattie (1), Xinya Xu (1), Yongtao Qu (1), Martial Duchamp (2), Utkur Mirsaidov (3), Stephen Campbell (1), Vincent Barrioz (1), Guillaume Zoppi (1)
Affiliations : (1) Department of Mathematics, Physics and Electrical Engineering, Northumbria University, Newcastle upon Tyne, NE1 8ST, United Kingdom (2) Laboratory for In Situ and Operando Electron Nanoscopy, School of Materials Science and Engineering, Nanyang Technological University, 637371, Singapore (3) Department of Physics and Centre for BioImaging Sciences, Department of Biological Sciences, National University of Singapore, 117557, Singapore

Resume : Global electricity generation is projected to be 5 times today’s level by 2070 [1]. Such growth defines a new era for photovoltaics (PV) because of the demand for innovative and sustainable distributed power sources. This creates an opportunity for inorganic thin film PV because of its stability and compatibility with a variety of substrates. Here, we present the results of two novel approaches to the fabrication of kesterite solar cells from scalable, Cu2ZnSnS4 (CZTS) nanoparticle inks. Firstly, CZTS nanoparticles are annealed in a Se-rich atmosphere for the first time inside a transmission electron microscope (TEM) [2]. This allows observation of the thin film PV absorber formation in real-time and provides the new insight that chalcogen atom exchange and grain growth occur in different temperature regimes. The technique is transferred to an industrially-similar furnace to achieve a 33% increase in the device VOC. The approach can be applied to any solar cell fabrication process that requires thermal annealing. Secondly, we demonstrate an approach to alkali doping Cu2ZnSn(S,Se)4 PV absorbers on flexible Mo-foil substrates [3] that is compatible with high volume manufacturing. Adding NaF directly to the CZTS nanoparticle ink promotes grain growth and improves the device efficiency to 4.5%. Importantly, the technique nearly eliminates a detrimental fine-grain CZTS layer associated with the nanoparticle ink synthesis. Finally, we present results from kesterite solar cells made with Cd-free buffer layers using the nanoparticle ink approach. These cells use In2S3 and offer 7.8% photovoltaic conversion efficiency. All results are discussed in the context of a new proposed sub-field, product integrated photovoltaics (PIPV). [1]. Shell International, B. V. Sky Scenario, [2]. Y. Qu, N. S. Beattie et al., ACS Appl. Energy Mater. (2019) [3]. X. Xu, N. S. Beattie et al., J. Mater. Sci.: Mater. Electron (2019) 30: 7883

Authors : A.J.N. Oliveira1,2, J. De Wild3,4,5, K. Oliveira1, B.A. Valença1, J.R.L. Guerreiro1, S. Abalde-Cela1, M. Prado1, T. S. Lopes1,3,4,5, R. M. Ribeiro1,2, J.M.V. Cunha1,6,7, M. A. Curado1,8, A. Violas1,2, J. P. Teixeira1, P. A. Fernandes1,6,9, B. Vermang3,4,5, P. M. P. Salomé1,7
Affiliations : 1 INL – International Iberian Nanotechnology Laboratory, Avenida Mestre José Veiga, 4715-330 Braga, Portugal; 2 Departamento de Ciência dos Materiais, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus de Caparica, 2829-516 Caparica, Portugal; 3 Imec division IMOMEC (partner in Solliance), Wetenschapspark 1, 3590 Diepenbeek, Belgium; 4 Institute for Material Research (IMO), Hasselt University (partner in Solliance), Agoralaangebouw H, Diepenbeek, 3590, Belgium; 5 EnergyVille 2, Thor Park 8320, 3600 Genk, Belgium; 6 I3N,Departamento de Física da Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal; 7 Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal; 8 CFisUC, Departamento de Física, Universidade de Coimbra, 3004-516 Coimbra, Portugal; 9 CIETI, Departamento de Física, Instituto Superior de Engenharia do Porto, Instituto Politécnico do Porto, Porto 4200-072, Portugal;

Resume : The presence of scarce and expensive elements in the Cu(In,Ga)Se2 (CIGS) composition, such as In and Ga, present a strong limitation to the large-scale production of these solar-cell devices. Therefore, the continuous reduction of the absorber thickness is of outmost importance in order to further decrease the material consumption and production cost. However, with such reduction, problems in the solar cells light absorption efficiency become more evident. The implementation of light management architectures, which can range from surface texturization to the integration of plasmonic nanoparticles, can be used in order to mitigate such optical losses. In this work, we propose a novel way of introducing gold nanoparticles in a solar cell structure, where the nanostructures are encapsulated with a dielectric layer protecting them from the CIGS harsh growth conditions. The proposed architecture was implemented in an ultrathin CIGS solar cell device through the combination of a bottom up chemical approach to deposit the nanostructures and a top down photolithographic procedure to create electrical contacts. With the proposed architecture, an enhancement of the light effective optical path of approximately 4 times the absorber thickness is demonstrated in the infrared region, through optical simulations. The new architecture leads to a short circuit current increase of 17.4 %, in comparison to a reference sample.

Authors : Uvarov, A.V.*(1), Gudovskikh, A.S.(1,2), Baranov A.I.(1), Kudryashov D.A.(1), Morozov I.A.(1)
Affiliations : (1) Alferov University, St. Petersburg, Russia (2) St. Petersburg Electrotechnical University “LETI”, St. Petersburg, Russia

Resume : Silicon-based solar cells are of the greatest interest for terrestrial photovoltaic because Si is relatively low cost. However, Si solar cells with efficiency exceeding 26% approached closely to the theoretical limit of single junction solar cells leaving almost no possibility for further improvement. The most efficient way to overcome this theoretical limit related to thermalization losses is to use multijunction solar cells. According to theoretical estimations a combination of top subcell with a band gap of 1.6–1.7 eV and Si (1.12 eV) bottom subcell could give an efficiency of more than 35% for dual junction solar cells. Low-dimensional structures provide possibility to achieve desired band gap by varying the width of the wells in superlattice-type structures. Thus GaP/Si superlattice could be efficiently used as an active material for top subcell of Si based photovoltaic devices. Previously n-doped GaP was obtained by PE-ALD at the temperature of 380°C. In this work using PE-ALD p-type GaP layer was obtained by introducing Zn dopant during the growth. For the first time plasma deposited p-i-n structures with GaP n- and p-type doped layers and an undoped region based on GaP/Si superlattices on a Si substrate showed a substantial internal quantum efficiency in the spectral range of 300-750 nm and almost complete absence of absorption at longer wavelengths, which indicates their promise for use in solar cells as the top-junction.

2D materials : Judith Driscoll
Authors : Syed Hassan Abbas Jaffery1*, Jongwan Jung1
Affiliations : Department of Nanotechnology & Advanced Materials Engineering, Graphene Research Institute, Sejong University, Seoul 143-747, Republic of Korea

Resume : Van der Waals heterojunctions based on atomically thin two-dimensional (2D) materials have attracted numerous attention for their special scientific research value and promising applications as a rectifier and photodiodes. In this research, photovoltaic properties of p-GeSe/n-MoTe2 van der waals heterojunctions were studied. It has been reported that GeSe has high photoresponsivity along the a3 (perpendicular to the plane) direction. The device was fabricated by mechanical exfoliation of GeSe and MoTe2. In order to reduce the schottky effect, Pd/Au contacts were fabricated with GeSe and Cr/Au contacts were fabricated with MoTe2. Pd/Au and Cr/Au contacts results in the ohmic contact with GeSe and Mote2 respectively. The devices were then subjected to NIR light illumination at a wavelength of 850 nm. GeSe/MoTe2 vdW heterojunction p-n diode showed excellent response to NIR laser. The diode exhibits excellent response at Vds = 0V and Vbg = 0V (self-powered). The rise and decay time are important factors in photodiode characterization. The rise and decay time of GeSe/MoTe2 p-n diode are 54ms and 55ms respectively. Excellent photoresponse, rise and decay time will assist in the development of efficient and high-performance photodetectors.

Authors : Balaji Dhanabalan, Yu-Chen Leng, Giulia Biffi, Miao-Ling Lin, Ping-Heng Tan, Ivan Infante, Liberato Manna, Milena P. Arciniegas, and Roman Krahne
Affiliations : Balaji Dhanabalan, Giulia Biffi, Ivan Infante, Liberato Manna, Milena P. Arciniegas, Roman Krahne, Istituto Italiano di Tecnologia (IIT), Via Morego 30, 16163 Genoa, Italy; Yu-Chen Leng, Miao-Ling Lin, Ping-Heng Tan, State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, China;

Resume : Two-dimensional (2D) layered perovskites are highly attractive materials for fundamental research and practical applications due to their natural inherent quantum well[1], improved stability [2], and the possibility of mechanical modulation of the photoluminescence[3] and exfoliation of single flakes[4]. The vibrational modes are of fundamental importance for their optoelectronic properties, as optical relaxation channels and heat dispersion depend on the vibrational mode spectrum and on the electron-phonon coupling.[5] We present an ultralow frequency Raman study of the vibrational modes of 2D layered perovskite materials in unprecedented detail. Our measurements on single flakes with controlled orientation of the linear polarization direction of the incident light to the 2D perovskite lattice allow to distinguish the geometrical properties of the lattice vibrations. Here the choice of the organic moieties can be used to tailor the in-plane anisotropy of the vibrational modes and their inter-layer coupling. Such insight provides a new toolbox for tailoring the optoelectronic properties of 2D layered perovskite structures and will boost their impact in optical and optomechanic applications. References: 1. L. Dou et al., Science 2015, 349, 1518. 2. H. Tsai et al., Nature 2016, 536, 312. 3. A. Castelli et al., Adv. Mater. 2018, 1805608. 4. B. Dhanabalan et al., Nanoscale 2019, 11, 8334. 5. X. Gong et al., Nat. Mater. 2018, 17, 550; F. Thouin et al., Nat.Mater. 2019, 18, 349.

Authors : AC Varonides
Affiliations : University of Scranton Physics & Engineering Dept USA

Resume : We study photo-carrier escape from quantum wells and their contribution to current, as they reach the continuum of the conduction band. By considering a superlattice layer (SL), embedded in the bulk of a Graphene/Oxide/n-GaAs solar cell, we calculate excess current due to electrons escaping from the quantum wells of the SL layer. We therefore solve for collective thermionic current out of quantum wells (from low-gap GaAs layers) through the populations of excess electrons in the eigenenergies. We treat the device as a metal-insulator-semiconductor (MIS) solar cell, where monolayer graphene replaces the metal. In addition, by inserting an AlAs/GaAs superlattice layer in the region near the depletion edge of the diode, we expect excess photo-current due to electrons surmounting the Schottky barrier thermionically. The collective effect of current out of quantum wells is treated and represented as a thermionic emission from the embedded SL region(TE/SL) current density. In addition to the superlattice effect, photo-current develops from the bulk cell structure due photo-carriers from several regions of the device. Such photo-excited carriers come from (a) the bulk of the semiconductor as minority holes in the n-GaAs and (b) photo-excited carriers (holes) from the depletion region. Note that such a design offers reduction of recombination losses in both super-lattice and depletion regions due to carrier separation from the quantum wells and the electrostatic field at the depletion region. We therefore treat carrier contribution to total current as the sum of three current components due to super-lattice-generated photo-carriers and minority photo-holes from the bulk semiconductor region and photoholes from the depletion region respectively. We find that the Schottky solar cell J-V characteristic J = Jo (exp (qV/kT)-1) – JL includes a new prefactor and the sum of the three photocurrent terms as mentioned above. The cell structure is essentially a graphene/n-GaAs Schottky cell with a superlattice layer in the bulk of the semiconductor. The Jo prefactor in the fundamental solar cell expression is different due to graphene replacing the metal. A new Richardson constant appears due to graphene’s different properties (graphene treated as a 2D medium with different density of states (DOS)). The cell design is a Schottky barrier solar cell with the metal replaced by a monolayer graphene film as the window of the device. Under one sun, a ten-period superlattice (each period at 50 nm), provides 0.45 mA/cm^2 of excess thermionic current, in addition, exposure at 400 suns generates total TE/SL current near 9 mA/cm^2.

16:00 Break    
Poster session 2 : Mutsumi Sugiyama
Authors : Toshihiro Miyata, Hiroki Tokunaga, Tadatsugu Minami
Affiliations : Optoelectronic Device System R&D Center, Kanazawa Institute of Technology

Resume : We recently reported photovoltaic properties of Cu2O Schottky-type heterojunction solar cells fabricated using Al-doped ZnO (AZO) transparent conducting thin films by a low-damage magnetron sputtering (MSD) method. These properties were higher than those of the pulsed laser deposition (PLD) method.1) In this paper, we describe photovoltaic properties of AZO/n-type oxide semiconductor thin film/Cu2O heterojunction solar cells using various multi-component n-type oxide semiconductor thin film layers, e.g., Zn-Ge-O, Zn-Ga-O, formed by a low-damage MSD method. The obtained photovoltaic properties of Cu2O heterojunction solar cells strongly depend on the sputter deposition conditions of the n-type oxide semiconductor layer. For example, in AZO/n-Zn-Ge-O thin film/p-Cu2O sheet heterojunction solar cells, an AZO thin film is laminated at DC 75 W on a Zn-Ge-O thin film, which is a multicomponent oxide semiconductor formed by the above MSD in a pure Ar+H2 gas atmosphere. The highest conversion efficiency of 3.74% was achieved. Because Cu2O sheets were vertically arranged using the rf power imposed dc-MSD method and hydrogen gas was used to form a Zn-Ge-O multi-component n-type oxide semiconductor thin film, a high-quality Zn-Ge-O multi-component n-type oxide semiconductor thin film/Cu2O interface could be produced with less damage due to excessive oxidation of the Cu2O surface. In conclusion, AZO/n-Zn-Ge-O thin film /p-Cu2O sheet heterojunction solar cells fabricated by vertically arranging Cu2O sheets using the rf+dc-MSD method and introducing hydrogen gas achieved a conversion efficiency drastically improved over that of AZO thin film/p-Cu2O solar cells. [1] T. Miyata et al., Journal of Semiconductors. 40, 032701 (2019).

Authors : Naruhide Kato and Muthumi Sugiyama
Affiliations : Tokyo University of Science

Resume : Visible-light-transparent solar cells are innovative devices that are used in various applications. Our group has produced visible-light-transparent solar cells that combine p-type nickel oxide (NiO) and n-type zinc oxide (ZnO), which are transparent oxide semiconductors (TOSs) and have been proposed as visible-light-transparent devices in the Internet of Things. In addition to the high transparency feature, TOSs are materials with high environmental resistance because of their large bandgap energy. In order to investigate the environmental resistance of visible-light-transparent solar cells, degradation properties of the devices in the harsh environment (such as radiation, thermal cycles, and ultraviolet ray’s) have been evaluated. In this study, the degradation phenomena of NiO-related visible-light-transparent solar cells was investigated. NiO-related visible-light-transparent solar cells were fabricated using reactive radio frequency magnetron sputtering because they are most suitable for economically depositing large-area films. Various resistance tests were carried out. The results reveal that NiO-related visible-light-transparent solar cells exhibit high resistance properties to proton irradiation compared to conventional space solar cells by approximately 10000 times. This result demonstrates the high environmental resistance of NiO-related visible-light-transparent solar cells and the possibility of their practical use as novel space- and ground-use solar cells.

Authors : Keisuke Nishimoto and Mutsumi Sugiyama
Affiliations : Tokyo University of Science

Resume : Nickel-Oxide (NiO) is an exotic material for visible-light-transparent photovoltaic applications that exhibits only p-type conductivity with a wide bandgap (4.0 eV). In addition, the carrier density of NiO is easily controlled by doping impurities like Li or by introducing intrinsic defects like Ni vacancies and/or interstitial O. Therefore, NiO has been used as both an insulator and a semiconductor with a carrier density in the order of 10^13 - 10^21 cm^-3. However, its defect properties have not been fully evaluated. In addition, very high-quality crystal films are needed for evaluating the intrinsic defect properties. Therefore, thin films of epitaxial NiO are expected to be used for defect properties evaluation. Recently, NiO films have been deposited using different methods, with sputtering being the most suitable for economically depositing large surface films with well-controlled compositions. However, the epitaxial growth mechanism of sputter-grown NiO has not been clarified because of the few existing studies. In this study, the crystal structure of thin epitaxial NiO films grown by RF reactive magnetron sputtering is investigated. Epitaxial NiO thin films were grown by RF reactive magnetron sputtering on (0001) Al2O3 and (100) MgO substrates under various substrate temperatures, RF power, and O2 partial pressure. The results show that on the sapphire substrate, the epitaxial thin NiO films have a different crystal structure between the interface and the surface.

Authors : Naoufel Khemiri, M. Kanzari
Affiliations : Université Tunis El Manar, Institut Préparatoire aux Etudes d’Ingénieurs El Manar, Campus Universitaire Farhat Hached, B.P 244, Tunis 2092, Tunisie. Université Tunis El Manar, Ecole Nationale d’Ingénieurs de Tunis, Laboratoire de Photovoltaïque et Matériaux Semi-conducteurs, B.P 37, 1002,Le Belvédère Tunis, Tunisie. Université de Tunis, IPEITunis Montfleury, Laboratoire de Photovoltaïques et Matériaux Semi-conducteurs-ENIT.

Resume : Over the last two decades, cadmium sulphide CdS synthesited by chemical bath deposition (CBD) was the most used buffer layer for thin film solar cells. However, the replacement of CdS in solar cells by other possible buffer layers is of high interest for several reasons. Indeed, CdS contains the toxic metal Cd which represents a threat to the human health and the environment and has a relatively low band gap of 2.4 eV which limits the performance and the efficiency of the cells. Zn(O,S) and (Zn,Sn)O oxide semiconductors are among the most promising Cd-free materials for replacing the CdS as earth abundant and non-toxic buffer layer in solar cells. In this work, we present experimental studies of both materials. (Zn,Sn)O and Zn(S,O) thin films were prepared by two steps method: The deposition of metalic precursors by thermal evaporation followed by an annealing in air or sulfur atmospheres. Using different characterization techniques such as UV-Vis-NIR spectroscopy, X-ray diffraction, atomic force microscopy, we demonstrate that both materials exhibit structural, morphological and optical properties that are suitable for photovoltaic applications.

Authors : Ngoc Minh Le, Jinhyeok Kim, and Byung-Teak Lee
Affiliations : Chonnam National University, Gwangju, Republic of Korea

Resume : Transparent conducting oxide (TCO) films play an essential role for various optoelectronic devices. Unfortunately, it is very difficult, if not impossible, to obtain high performance TCO films with both of high optical transparency and high electrical conductivity. In this work, properties of ZnO-based multilayer films, with high conductivity, high transmission, and large energy bandgaps, and their device performances have been investigated. It was observed that the GaZnO/InCdO/GaZnO multilayer films showed excellent properties of ~90% average transmittance over visible/IR range and 7.5×10-5 Ω·cm resistivity. Efficiency of the CuInGaSe solar cells using this multilayer structure as the front electrode shows much higher efficiency (8.5%) than that (4.7%) of the devices with GaZnO electrodes. The ZnMgBeO/Cu/Ag/ZnMgBeO multilayer structure also showed excellent properties, with ~ 90% average transmission, 1.7×10-4 Ω·cm resistivity, and 6.0 eV energy bandgap. Results of the solar cell fabrication, however, indicated somewhat deteriorated performance, probably due to the high “vertical” resistivity. Further discussions on the detailed observations, as well as results on the oxide films with larger energy bandgaps, will be discussed during the presentation.

Authors : Jiyoon Park, Gun Young Jung
Affiliations : School of Materials Science and Engineering (SMSE), Gwangju Institute of Science and Technology (GIST), 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Republic of Korea.

Resume : Organo-lead halide perovskite materials have been considered for the next generation solar cells thanks to superior absorption properties in the visible light range, which were originated from their inherent bandgap of about 1.55 eV. However, this point serves as the biggest limitation for improving the power conversion efficiency (PCE) of perovskite solar cells (PSCs), meaning that the PSCs rarely utilize the non-visible sunlight. To overcome this limitation, many researchers have incorporated the up-conversion nanoparticles (UCNPs) into PSCs. However, because the UCNPs were generally contained and dispersed in solutions (de-ionized water; D.W. etc.), there was a limitation to transfer the UCNPs into PSCs due to its vulnerable nature to H2O. Moreover, a low quantum yield of up-conversion efficiency (UCE) of UCNPs (~1 %) was an obstacle to obtain dramatically enhanced PCE. In this work, we applied a simple dry transfer method to transfer the UCNPs within PSCs. Since no solvent such as D.W. was needed during the transfer of UCNPs within PSCs, UCNPs were transferred without any damage to perovskite film. After that, gold (Au) top electrode was deposited on UCNPs/HTL. Herein, the Au was acting as not only top electrodes, but also the plasmonic substances. Surface plasmonic resonance (SPR) was induced by using Au top electrode, which led to an increase in the UCE of UCNPs. Therefore, an average PCE of 15.56 % was obtained in that case, which was enhanced by 8.4 % compared to reference cell. This improvement was attributed to NIR light utilization due to the plasmon-enhanced UCNPs originating from the Au top electrode.

Authors : Kulish, M.R. (1), Kostylyov, V.P. (1), Sachenko, A.V. (1), Sokolovskyi, I.O. (1), & Shkrebtii, A.I.* (2).
Affiliations : (1) V. Lashkaryov Institute of Semiconductor Physics (ISP), NAS of Ukraine, 45 Pr. Nauky, Kyiv, 03028, Ukraine; (2) Ontario Tech University, 2000 Simcoe St. N., Oshawa, ON, L1G 0C5, Canada. *

Resume : Luminescent solar concentrators (LSC) photovoltaic concept attracts lately a lot of attention [1]. In view of recently developed cost competitive low-temperature sol-gel fused quartz synthesis with simultaneous quantum dots (QD) luminophore doping, we first critically revisited available experimental results for main types of LSC waveguide matrices. To maximize the photoconversion efficiency, we carried out their parameters comparison to formulate the basic requirements for transparent matrix materials, including, e.g., high transparency for sunlight (not less than 98%), particularly in the spectral range of the luminophores’ emission, and sufficiently high refractive index (above 1.5). We established spectral range for these materials that minimize light absorption. To ensure LSC stable characteristics for 20-30 years, chemical and temperature stability, mechanical hardness are also required. Even though PMMA matrix currently dominates in LSCs (due to well-established luminophore doping and luminescence quantum yield close to unity), fused quartz wide 0.25-2.5 μm transparency range is advantageous as compared to only 0.4-0.85 μm range of PMMA. Considering higher mechanical and chemical stability, and lesser toxicity of fused quartz, we simulated its LSC matrix, including role of its refractive index, the critical angle, luminescent photons losses due to escape-cone and other important parameters. [1] R. Mazzaro, et al. Advanced Energy Materials 8, 1801903 (2018)

Authors : Garima Aggarwal, Nawaf A, K. R. Balasubramaniam
Affiliations : Department of Energy Science and Engineering, Indian Institute of Technology Bombay, Mumbai-400076, India

Resume : Cu2O is a potential absorber material for solar photovoltaic and water-splitting due to its direct band gap of 2.0 eV, high absorption coefficient (10^4 cm^-1), and preferable conduction band alignment. The inevitable formation of Cu-vacancy (V_Cu) and its complex intrinsically make it a p-type semiconductor. However, these defects also act as trap centres which impede charge carrier transport by affecting hole mobility. Maximum efficiency (8.1 %) for Cu2O solar cells was based on thermally oxidized Cu2O, which shows the least acceptor defect density (10^14 cm^-3). To further decrease the acceptor defect density and enhance charge transport, we propose passivation of V_Cu by Cu-doping. The resultant lower free carrier density is not of much concern here as enough carriers get generated upon illumination. Cu2O, prepared by Cu-foil oxidation at 1000 ⁰C in air is studied using temperature dependent Hall measurement. Cu is doped at different temperatures ranging from 300 - 800 ⁰C in Ar ambient (1 to 10^-5 bar). It is observed that passivation of V_Cu by Cu-atom is limited by the low formation energy of Cu-interstitial (Cu_i) at process temperatures. Also, increased concentration of Cu at interstitial favours the formation of another defect complex, which is observed experimentally for the first time. Formation of this complex along with Cu_i further tends to decrease the hole mobility from 80 to 30 cm^2/V-s. This suggests that doping possibility of cations needs to be further studied.

Authors : R. Vollondat*(1), A. Ameur(1), S. Roques(1), J.L Rehspringer(2), D. Muller(1), C. Chevalier(3), A. Slaoui(1), T. Fix(1).
Affiliations : (1) CNRS and Université de Strasbourg, ICube Laboratory, 67037 Strasbourg, France; (2) CNRS and Université de Strasbourg, Institut de Physique et Chimie des Matériaux de Strasbourg, 67034 Strasbourg, France; (3) Institut des Nanotechnologies de Lyon, INSA Lyon, 69621 Villeurbanne, France.

Resume : Common forms of elemental silicon (mono-, multi-crystalline and amorphous) play a foundational role in the field of electronics and the underlying technologies are well mastered. Exotic, low-density forms of silicon obtained have recently regained interest due to alluring semiconducting properties as thin-films. Here we focus on an allotrope of silicon: silicon clathrate thin-films. Clathrates are structures defined by a 3D porous framework (Si or group IV elements) of polyhedrons, which can encloses guest-atoms (Na or alkali metals). Due to this specific organization, some silicon clathrates can exhibit an interesting direct band-gap of 1.8-2 eV, at low guest-atom occupancy, which is interesting for both optoelectronic and photovoltaic applications. Moreover, this band-gap is tunable by modifying the amount/nature of the guest-atoms or using Si/Ge alloys framework. In this work, we describe the preparation and characterization of silicon clathrate thin-films using different substrates (p-doped and intrinsic c-Si (100) and (111), a-Si on sapphire...). The structural, electrical, optical, surface properties are analyzed and the fabrication conditions optimized to give the best properties and mechanical integrity. Ion implantation experiments and other doping techniques are investigated to tune the clathrates properties. Furthermore, early devices are fabricated in order to estimate the potential of this material for photovoltaic and optoelectronic applications.

Authors : Katarzyna Gawlińska-Nęcek 1, Zbigniew Starowicz 1, Robert Socha 2, Bogusława Adamczyk-Cieślak 2, Grzegorz Putynkowski 4, Piotr Panek 1
Affiliations : 1 Institute of Metallurgy and Materials Science, Polish Academy of Sciences, Reymonta 25 St., 30-059 Krakow, Poland 2 Jerzy Haber Institute of Catalysis and Surface Chemistry Polish Academy of Sciences, Niezapominajek 8 St., 30-239 Krakow, Poland 3 Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska St. 141, 02-507 Warsaw, Poland 4 CBRTP – Research and Development Center of Technology for Industry, Złota St. 59, 00-120 Warsaw, Poland

Resume : Copper oxides are a p-type semiconductor materials with a band gap energy in the range from 1.2 – 2.1 eV and great potential for use in thin-film solar cells. Common methods of CuO copper oxides manufacturing are magnetron sputtering, chemical vapor deposition or thermal oxidation. However, their main problem is providing a non-single phase layer which is usually a mixture of tenorite (CuO) and cuprite (Cu2O). Therefore, in this presentation, we propose a paste sintering method for pure CuO layer manufacturing. The CuO paste used for the experiment was a commercial CuO component in an organic medium. The paste was deposited on a substrate by using screen printing method and subsequently fired in a resistance furnace at the temperature of 850 - 1000°C in air. At temperatures of 850 and 900°C for 30 min., no crystallization of the layer occurs. What is more, the lower the firing temperature was, the worse layer adhesion to the substrate was reported. When burning at 950°C within 30 minutes, the layer is almost crystallized, although a numerous of unfilled spaces between the grains could be seen. At 1000°C for 10 minutes resulted in a lack of structure continuity and large crystallites which diameter is even 6 m. Shortening the firing time at 1000°C to 1 minute allowed to obtain a fully compact structure without any holes. X-ray analysis indicated that the layer produced is a single-phase CuO. Optical and material parameters of CuO layers were also obtained as a result of spectrophotometric analysis. The resistance measurement confirmed high resistivity of the formed oxide layers, which increases with firing temperature increasing.

Authors : Alekseev, P.A.*(1), Nyapshaev, I.A. (1,2), & Terukov, E.I(1,2).
Affiliations : (1)Ioffe Institute, St. Petersburg, 194021 Russia; (2) R&D Center for Thin Film Technologies in Energetics, St. Petersburg, 194021 Russia

Resume : Efficiency of the solar cells can be increased by harvesting both solar and mechanical energy. Recently, several concepts utilizing solar and mechanical energy by hybrid semiconductor devices were presented. We showed InP/Si heterostructure for triboelectric/photovoltaic generation where triboelectric current was produced by sliding a conductive tip across InP surface while photocurrent was generated at the InP/Si interface. Unfortunately, tribo- and photocurrents had an opposite polarity due to relatively high surface state density at the Me/InP interface. Recently Hao et al. [2] and Liu et al. [3] presented synergetic co-harvesting of the solar and mechanical energies at the interface between sliding metal tip and a perovskite or p-Si, respectively. Motion of the conductive electrode non-linearly increased a solar cell harvesting at the moving electrode/semiconductor interface. Here, we studied a triboelectric/photovoltaic generation by the moving of the conductive tip of the atomic force microscope across the bare surface of the p-a-Si/i-a-Si/n-Si/i-a-Si/n-mc-Si/ITO heterojunction solar cell. Motion led to the increasing of the open-circuit voltage (Voc) from 630 mV to 640 mV with simultaneous increasing of the short-circuit current (Isc) density by 15%. This work is supported by Russian Science Foundation (RSF) project 18-72-00104. [1] Sharov V.A., et al.//ACS Appl. Energy Mater., 2, 4395 (2019) [2] Hao Z., et al.//Matter, 1, 639 (2019) [3] Liu J., et al.//Matter, 1, 650 (2019)

Authors : Pablo Sánchez-Palencia,1,2 Gregorio García,1,2 Pablo Palacios,1,3 Perla Wahnón,1,2
Affiliations : Instituto de Energía Solar, ETSI Telecomunicación, Universidad Politécnica de Madrid, Ciudad Universitaria, s/n, 28040, Madrid, Spain; (G.G) 2 Departamento de Tecnología Fotónica y Bioingeniería, ETSI Telecomunicación, Universidad Politécnica de Madrid, Ciudad Universitaria, s/n, 28040 Madrid, Spain 3 Departamento de Física aplicada a las Ingenierías Aeronáutica y Naval. ETSI Aeronáutica y del Espacio, Universidad Politécnica de Madrid, Pz. Cardenal Cisneros, 3, 28040 Madrid, Spain.

Resume : Indium-phosphide (InP) is a widely studied III-V semiconductor material with adequate properties (such as a direct bandgap close to the optimum for solar energy conversion and high crystallinity) to be used as absorber material in photovoltaic cells. This work assesses the possibility of increasing the photovoltaic efficiency of InP semiconductor through hyperdoping with transition metals (TM = Ti, V, Cr, Mn). For this, electronic band and optical absorption features of TM-hyperdoped InP (TM@InP), with general formula TMxIn1-xP, have been deeply studied by using accurate ab-initio electronic structure calculations. TM replacement does not lead to an important crystal structure distortion, while the energetic of the hyperdoping process evidence the possibility of obtaining TM@InP materials. The analysis of the electronic structure shows that TM 3d-orbitales induce new states in the host semiconductor bandgap, leading to improved absorption features that cover the whole range of sunlight. The best results are obtained for Cr@InP, which is an excellent candidate as in-gap-bap (IGB) absorber materials. Thus, the sunlight absorption in considerably improved through new-sub-bandgap transitions across de IGB. Our results provide a perspective on the effects of transition metal hyperdoping into the exploitation of new semiconductor materials with improved sunlight absorption performance.

Authors : Mikel Fernando Hurtado Morales. *(1), Carlos Felipe Reyes Bello (1), Daniel Felipe Bohórquez Vargas (1).
Affiliations : (1) Department of Electronic Engineering, Central University, Bogotá, Colombia.

Resume : In the present work will be exposes the development of a designed device that carry out thin film growth processes, using chemical bath deposition technique (CBD). The device has four reactors for the location of different solutions, each reservoir has an agitation control to prevent precursors precipitation in the system, a temperature control and monitoring up to 60 ° C, using power resistors and a fiberglass coating as a thermal conductor, additionally its structure allows the movement and immersion of the substrate through the different reservoirs in a fully automated way. Through the graphical interface, it is possible to monitor the entire process, in addition to configuring the order and immersion time of the substrate and at the same time controls the temperature and agitation of each solution. For the validation of the device, copper sulphide (Cu2S) growth tests were performed, for this purpose a solution consisting of 25ml of copper chloride (CuCl2) 0.1M, 2.5ml of triethanolamine (TEA - C6H15NO3) and 5ml of thiourea (CH4N2S) 1M were used. Subsequently the temperature of the first container was set with the solution at 50 ° C, during 25 min (immersion time) and a moderate agitation, during the immersion the solution was dosed with ammonia (NH3) until reaching a total of 50ml. The acquired thin films were analyzed by scanning electron microscope SEM-EDS technique, where the nano-zise crystals around 100 nm of Cu2S are evident. The calculated band-gap using UV-Vis spectroscopy suggests adequate optoelectronic properties to be used nano-size Cu2S as absorber layer in thin film solar cell devices.

Authors : H. Ferhati1, F. Djeffal1, and A. Benhaya1
Affiliations : 1 LEA, Department of Electronics, University Mostefa Benboulaid-Batna 2, Batna 05000, Algeria. E-mail: Tel/Fax: 0021333805494

Resume : The multijunction solar cells promise to reduce the cost of solar photovoltaic energy production significantly through high power conversion efficiencies. Nevertheless, monolithic multijunction solar cells often have efficiency losses due to current‐mismatching tolerated in the interests of lattice matching. Therefore, new approaches should be developed to reduce these losses. One of the proposed techniques for enhancing the power conversion efficiency is to split sunlight into suitable spectral bands for a set of solar cells with appropriate energy band gaps. In this paper, metal/Oxide/metal meshing is used as a new concept to enhance the light splitting properties. Finite difference time domain (3D-FDTD) modeling is carried out to investigate the impact of engineered layers on the spectral beam splitter performances. Our investigation demonstrates that metal layer and Oxide material are responsible for light splitting effects, where their geometry and position play an important role in modulating the spectral beam splitter optical properties. Besides, an enhanced optical performance over the conventional spectral splitter is recorded by developing a new hybrid modeling approach based on 3D-FDTD supported by Genetic Algorithm (GA) optimization to identify the intermediate metallic layer and oxide films. Therefore, the proposed approach can offer a novel systematic strategy for designing high-performance spectral beam splitter coating layers for multijunction photovoltaic applications.

Authors : G. El Hallani1, M. Khuili1, S. Nasih2, N. Fazouan1,2,*, A. Liba1, L. Laanab 3, O. Mounkachi 4, A. Mzerd 5, E. H. Atmani2
Affiliations : 1 Physical Materials Laboratory. Faculty of Sciences and Technologies, Beni Mellal, Morocco 2 Physics of Condensed Matters and Renewables Energies Laboratory. Faculty of Sciences and Technologies, Mohammedia, Morocco 3 Conception Systems Laboratory, Faculty of Sciences, Rabat, Morocco 4 Condensed Matter and Interdisciplinary Sciences Laboratory, Faculty of Sciences, Rabat, Morocco 5 Group of Semiconductors and Environmental Sensor Technologies-Energy Research Center, Faculty of Science, Mohammed V University, Rabat, Morocco

Resume : Transparent Conductive Oxides (TCO) in solar cells are used as transparent electrodes. They must necessarily have a high optical transmission in order to allow efficient transport of photons to the active layer and also good electrical conductivity which is required to obtain the least losses of transport of photo-generated charges. Aluminum, Magnesium and Tin doped ZnO thin films are some of these. In this contribution, the TCO materials formed of Al, Mg and Sn doped ZnO thin films (AZO, MZO, TZO) were synthesized by spin coating method. The structural, optical and electrical properties of these films are investigated as a function of dopant concentration. X-ray diffraction patterns show that all AZO, MZO and TZO films exhibit the hexagonal würtzite structure with a preferential orientation along [002] direction with no additional peak corresponding to secondary phases. The surface morphologies show that AZO and MZO films are homogeneous and dense while TZO films showed different surface morphologies going from homogeneous to porous structure depending on Sn concentration. An enhancement of optical transmittance of about 95% with a blue shift of the gap energy was found for both Al and Mg doped ZnO layers against 70% of average level transmittance and a red shift of optical window for Sn doped ZnO films. Photoluminescence (PL) measurements at room temperature shows excitonic peaks corresponding to the AZO, MZO and TZO films with a low defects level for 1% Al doped ZnO compared to MZO and TZO films that showing a large intensive band defects centred around 514 nm characterizing the substitution defects of the zinc atoms by oxygen atoms. Electrical measurements show that all the films present an Ohmic comportment with a best electrical conductivity of 2.45 obtained for 1% AZO in accordance with the photoluminescence analysis. The reduced electrical conductivity shown in our films is attributed to the low mobility of charge carriers due to their diffusion by the grain boundaries.

Authors : D. Suchet1,2,3, A. Delamarre2,3, N. Cavassilas2,3,4, Z. Jehl2,3, Y. Okada2,3, M. Sugiyama2,3, J.-F. Guillemoles1,2,3
Affiliations : 1 IPVF, UMR 9006, Palaiseau, France 2 LIA NextPV, CNRS - The University of Tokyo, Tokyo, Japan 3 Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo, Japan 4 Aix Marseille Université, CNRS, Université de Toulon, Marseille, France

Resume : The concept of intermediate band solar cell (IBSC) was introduced 20 years ago as an innovative way to overcome the celebrated Shockley Queisser limit by harvesting low energy photons [1]. Since then, IBSC have received much attention both from a theoretical and experimental perspective. Yet, despite these efforts, no working proof of concept could be achieved, notably due to the important voltage loss induced by recombination. It was recently suggested that a slight energy shift in the intermediate transition – an electronic ratchet – could increase the efficiency of IBSC [2]. We have shown that this feature is not a mere improvement of the IBSC concept, but is actually mandatory to outmatch the Shockley Queisser limit [3] as soon as non-idealities such as non radiative recombinations and narrow transitions were taken into account [4]. Furthermore, we offer a physical explanation of the influence of the ratchet by performing an analytical optimization [5]. Using Lagrange multipliers, we show that the ratchet allows the system to match photo-currents to- and from the intermediate band while preventing voltage degradation. By lifting a constraint set on the energy gaps, the ratchet thus allows the system to take the best of both worlds: the open circuit voltage and fill factor from a single junction, but the current increase of an IBSC. [1] Luque A., Marti A., Phys Rev Lett, 78, 26 (1997) [2] M. Yoshida et al., Appl. Phys. Lett. 100, 263902 (2012) [3] A. Delamarre, D. Suchet, N. Cavassilas et al., IEEE JPV, 8, 6 (2018) [4] N. Cavassilas, D. Suchet, A. Delamarre et al., EPJ Photovoltaics 9, 11 (2018) [5] D. Suchet, A. Delamarre, N. Cavassilas et al., Prog. in PV, 26, 10, pp. 800 (2018)

Authors : Franco Josue Amaya Suazo, Katia del Carmen Martinez Guzman, Sadasivan Shaji, David Avellaneda, Bindu Krishnan
Affiliations : Facultad de Ingeniería Mecánica y Eléctrica, Universidad Autónoma de Nuevo León. San Nicolás de los Garza, Nuevo León, México.

Resume : Recently, perovskite solar cells have triggered a huge scientific interest in the photovoltaic field due to the outstanding performance of lead-based hybrid perovskite-based devices. This has led the researchers to develop cesium tin halide based perovskites such as Cs2SnI6 owing to its near ideal optoelectronic properties towards the development of stable, non- toxic and high efficient solar cells. In the present work, we report fabrication of p-n junction solar cells using spray coated Cs2SnI6-nano Si hybrid films as absorber and chemically deposited CdS as window layers. The Si-nanocolloids were formed by pulsed laser ablation in using silicon target in DMF. The best device showed a Voc higher than 0.8 V, Jsc of 1.5 mA/cm2 and FF of 0.5. Detailed studies on the changes in the crystalline structure, morphology, photophysical properties of Cs2SnI6 films due to incorporation of Si nano particles were done. A comparative analysis of X-ray diffraction patterns showed that the crystal structure remained cubic (Fm3m group) and air-stable. Nevertheless, the electrical conductivity and the photoconductivity were improved by incorporating the nanoparticles. An in-depth analysis of the devices formed at different conditions will be presented. This study provides very useful insights into the development of stable inorganic lead-free perovskites films by spray deposition, and also the in situ incorporation of nanoparticles to improve their photovoltaic properties.

Authors : Jonatan Fast, Enrique Barrigon, Mukesh Kumar, Yang Chen, Lars Samuelsson, Magnus Borgström, Adam Burke, Heiner Linke
Affiliations : Solid State Physis and Nanolund, Lund University, Lund, Sweden

Resume : The concept of hot carrier photovoltaics (HCPV) is to extract carriers excited to energies above the bandgap (hot carriers), before they have time to relax to the band edge via electron-phonon scattering. Semiconductor nanowires offer a promising platform for such devices for several reasons: the ability to grow highly lattice mismatched heterostructures [1]; observations of increased hot carrier temperatures [2]; and a geometry well suited for spatial control of light absorption. We have realized a HCPV device based on single InAs nanowires containing a small axial segment of InP at the center of the nanowire.[3] The InP segment serves as a filter that transmits only energetic electrons. This allows a current to be generated from a hot carrier distribution on one side of the filter. The device has been observed to generate an open-circuit voltage above the Shockley-Queisser limit for InAs under global illumination.[3] Using an electron beam induced current (EBIC), we have with high precision locally excited hot carriers within the nanowire to demonstrate its operational mechanism. At the spring meeting these results will be presented together with ongoing work on optimizing the performance of the device. [1] Caroff, P. et al., Nanotechnology, 2009, 20(49), 49560 [2] Tedeschi, D. et al., Nano Letters, 2016, 16(5), 3085-3093. [3] Limpert, S., Burke, A., Chen, I. et al., Nanotechnology 28, 434001 (2017).

Authors : Melanie Micali (1,2), Salvatore Cosentino (1,2), Antonio Terrasi (1,2).
Affiliations : (1) Dipartimento di Fisica, Università di Catania, via S. Sofia 64, I-95123, Catania, Italy (2) IMM-CNR, Sede Catania (Università), via S.Sofia 64, 95123 Catania, Italy

Resume : Transparent Conductive Materials (TCM) are of great importance for many opto-electrical devices and energy applications. Tin-doped indium oxide (ITO) is the most used TCM due to its high transparency (~ 80%) and low resistivity (10^(-2)-10^(-3) Ωcm). However, its large-scale usage faces the issue of scarcity, price and toxicity of In. Doping indium oxide with a transition metal (Mo, Zr, Hf, Ta) has been proposed as potential strategy to improve conductivity and transparency in ultra-thin TCM and, at the same time, reduce the amount of In. In this work, we show a highly conductive and transparent TCM based on Mo-doped ITO (ITMO). Thin films (~100nm) of ITMO with different concentrations of Mo dopant were deposited by RF magnetron co-sputtering from ITO and Mo targets. Post-deposition thermal annealing, up to 400°C, was performed to improve optical and electrical properties. Samples have been optically and electrically characterized using UV-VIS-NIR spectrophotometry and 4-points electrical probe. Our ITMO shows resistivity as low as 10^(-4) Ωcm and high wide range transparency of ~ 80% in the 400-2000 nm spectral range, after a thermal process at T lower than those reported for Indium Molybdenum Oxide (IMO). Rutherford-backscattering spectrometry and X-Ray photoelectron spectroscopy allowed us to clarify the role of Mo as effective dopant in ITMO films. These results will be discussed and help to shed light on new strategies to improve the properties of next generation TCM.

Authors : Min Kim,(1) Marcello Righetto,(2) Giovanni Perotto,(3) Michele Serri, (4) Mirko Prato,(4) Nicola Dengo,(2) Silvia Gross,(2,5) Gaudenzio Meneghesso,(5,6) Annamaria Petrozza,(1) Teresa Gatti (7) and Francesco Lamberti (2,5,6)
Affiliations : 1. Center for Nano Science and Technology, Istituto Italiano di Tecnologia, Via Pascoli 70/3, 20133 Milano, Italy 2. Department of Chemical Sciences, University of Padova and INSTM UdR Padova, Via Marzolo 1, 35131 Padova, Italy 3. Nanophysics Department, Smart Materials Lab, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy 4. Materials Characterization Facility, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy 5. Center “Giorgio Levi Cases” for Energy Economics and Technology, Via Marzolo 9, 35131 Padova, Italy 6. Department of Information Engineering, University of Padova, Via Gradenigo 6/B, 35131 Padova, Italy 7. Center for Materials Research, Justus Liebig University Giessen, Heinrich Buff Ring 17, 35392 Giessen, Germany

Resume : The development of cost-effective hole-transporting materials (HTM) that are capable of providing stable solar cells under variable or even extreme environmental conditions is of paramount importance to prospect an effective commercialization of emerging third-generation photovoltaic technologies.[1] We study here an organic-inorganic composite HTM based on a semiconducting poly(3-hexylthiophene) (P3HT) matrix used to disperse copper thiocyanate nanoplatelets. The choice of this particular materials combination comes from rational design of the HTM, based on exploiting the ease of processing a polymer as P3HT and the electron-blocking ability of a high-band gap semiconductor as CuSCN. Such composite HTM is tested in a standard architecture perovskite solar cell (PSC) maintained for one month in a water-saturated atmosphere, ensuring the maintenance of a good power conversion efficiency of more than 9%. This remarkable stability in conditions which would normally cause a fast deterioration of the perovskite layer, is interpreted as a CuSCN-mediated in-situ p-doping of the P3HT HTM, happening in the presence of water molecules permeated within the layer, that are locally converted into molecular oxygen. References [1] a) F. Lamberti, T. Gatti, E. Cescon, R. Sorrentino, A. Rizzo, E. Menna, G. Meneghesso, M. Meneghetti, A. Petrozza, L. Franco Chem 2019, 5, 1806-1817. b) T. Gatti, F. Lamberti, P. Topolovsek, M. Abdu-Aguye, R. Sorrentino, L. Perino, M. Salerno, L. Girardi, C. Marega, G. A. Rizzi, M. A. Loi, A. Petrozza, E. Menna Solar RRL, 2018, 2, 1800013.

Authors : Sourav Bose (a,b), Christyves Chevallier (a,b), Sidi Ould Saad Hamady (a,b), Jean-François Pierson (c), David Horwat (c), Nicolas Fressengeas (a,b)
Affiliations : (a) Université de Lorraine, Laboratoire Matériaux Optiques, Photonique et Systèmes, EA 4423, Metz, F-57070, France (b) CentraleSupélec, Laboratoire Matériaux Optiques, Photonique et Systèmes, EA 4423, Metz, F-57070, France (c) Université de Lorraine, Institut Jean Lamour, UMR7198, Nancy, F-54011, France

Resume : All-oxide photovoltaics is a new and very promising technology for low cost and efficient solar cells using earth-abundant and environmentally compatible materials. The main materials developed in this technology are cuprous oxide (Cu2O) and related compounds. Minami’s group [1] used a combination of costly Pulsed Laser Deposition (PLD) and thermal oxidation techniques to elaborate these promising materials and developed a solar cell with 8.1 % of photovoltaic efficiency. This efficiency, high for a proof-of-concept, was obtained with a ZnxGe1-xO buffer layer on Cu2O absorber. The germanium composition in ZnxGe1-xO can be engineered to obtain band alignment with the absorber. The complex and costly laboratory techniques used by the Minami's group permitted to show the feasibility and pave the way toward efficient all-oxide solar cells. Such techniques can however not be used in the solar cell industry where the main key is the efficiency to cost ratio. In this work, we used the low-cost ultrasonic spray pyrolysis technique (no vacuum, low temperature, large area deposition) to elaborate the high-potential oxide materials based on these compounds which can be easily transferable to industry. These materials properties were investigated, with respect to the elaboration parameters, using morphological characterization (profilometry, AFM), Raman spectroscopy and electrical transport measurements (Hall mobility, carrier concentration). The main growth parameters conditions investigated in this work are the temperature, pressure, deposition speed and flux. In addition, the impact of these parameters was evaluated in relationship to the photovoltaic application. [1] Minami et al., Applied Physics Express 9, 052301 (2016),

Authors : R. Pietruszka, B.S. Witkowski, M.Ozga, M. Godlewski
Affiliations : Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland

Resume : Atomic Layer Deposition (ALD) method found new applications in the field of photovoltaics. First of all, ALD deposited layers are used as passivating layers for silicon-based solar cells, as anti-reflective layers, and, as we show, as transparent conductive electrodes (TCO layers). Other possible applications include use of ZnO as a buffer layer and/or as a n-type emitter in modified Si-based solar cells. The latter application we demonstrated recently [1-3]. In our work, we show solar cells based on a n-type ZnO structures (layers and nanorods). ZnO/p-type Si photovoltaic cells were constructed on silicon wafers with thicknesses of 170 μm and 50 μm, using developed by us 3D electrode based on ZnO nanorods. For 170 μm thick solar cells, we received light conversion efficiency up to 14%. For thinner silicon wafers (50 μm) the Jsc value decreases from 38 mA/cm2 to 30 mA/cm2, whereas the Voc remains similar, of about 500 mV. The solar cells efficiency was ~10%. Further modification includes passivation of the rear contact (like in standard PERC solar cells). Thin aluminum oxide (Al2O3) layer is deposited between Al-contact and back side of silicon. Using laser cutter, small dot patterns are cut in the Al2O3 before deposition of Al contact. The results for these modified cells will be presented. This work was partially supported by the National Centre for Research and Development TECHMATSTRATEG1/347431/14/NCBR/2018. 1. R. Pietruszka, et al., Solar Energy 155 (2017) 1282-1288. 2. R. Pietruszka, et al., Solar Energy Materials & Solar Cells 147, (2016) 164-170. 3. R. Pietruszka, et al., Solar Energy Materials & Solar Cells 143, (2015) 99–104.

Authors : Selina Goetz (1,2), Theodoros Dimopoulos (1), Markus Valtiner (2), Giovanni Ligorio (3), Emil J.W. List-Kratoschvil (3), Christian Linke (4), Enrico Franzke (4), Jörg Winkler (4)
Affiliations : (1) AIT Austrian Institute of Technology, Giefinggasse 4, 1210 Vienna, Austria; (2) Vienna University of Technology, Applied Interface Physics, Wiedner Hauptstraße 8-10, 1040 Vienna, Austria; (3) Institut für Physik, Institut für Chemie & IRIS Adlershof, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 6, 12489 Berlin, Germany; (4) Plansee SE, Metallwerk-Plansee-Str. 71, 6600 Reutte, Austria

Resume : Molybdenum oxides (MoOx) are widely used materials in electronics, sensors, electrochromic devices, photovoltaics, organic LEDs and other applications, due to their adaptable electronic and optical properties arising from the existence of various oxide stoichiometries, such as MoO3 and MoO2. In the present study, thin MoOx films were sputter-deposited from an electrically conductive ceramic target using different oxygen partial pressures in the plasma, leading to different film stoichiometries. The films’ optical, electronic and structural properties were investigated and correlated to their stability in water that is particularly important for further applications. We show that layers with higher oxygen content have increased solubility in water. More specifically, the stability of the thin films was measured in an ICP-MS set-up, allowing to monitor the dissolution of the film in water over time, as well as the totally dissolved material. While the film’s stability increases with decreasing oxygen content, the film’s transparency rapidly decreases. Amongst others, this trade-off is unfavorable for the application of MoOx as a transparent selective contact in devices such as organic and hybrid solar cells. To this end, we show that molybdenum oxide compounds alloyed with additional elements lead to a significant increase in water stability, while maintaining favorable optical properties for the implementation in such devices.

Authors : Wei Zhao(1), Cendra Rakotoarimanana(2), Ahmed Ben Slimane(3), Nicolas Moron(4), Jean-François Guillemoles(3), Arnaud Etcheberry(2), Anne Marie Goncalves(2), Laurent Lombez(3), Baptiste Bérenguier*(3).
Affiliations : (1) Institut Photovoltaïque d'Ile de France, 18 boulevard Thomas Gobert, 91120 Palaiseau France (2) ILV - Institut Lavoisier de Versailles UMR 8180 CNRS/UVSQ Université de Versailles Saint-Quentin-en-Yvelines (3) CNRS, UMR IPVF 9006, 18 boulevard Thomas Gobert, 91120 Palaiseau France (4) GeePs, Group of electrical engineering - Paris, CNRS, CentraleSupélec, University Paris-Sud, Université Paris-Saclay Sorbonne Universités, UPMC Univ Paris 06

Resume : III-V semi-conductors are recognized as high-performance materials for the fabrication of (opto)electronics devices such as avalanche photodiodes, light emitting diodes and lasers. In this case, advanced contactless photoluminescence characterization is known as a powerful approach to determine carriers’ dynamics and recombination mechanisms. One classical method called Time Resolved Photoluminescence (TRPL) has been commonly used for probing fast recombination mechanisms under the nanosecond regime in thin film semi-conductors. The interpretation of the TRPL temporal decays may be difficult when presenting non mono-exponential behavior. Even a mono exponential decay is not necessarily an indication of a simple recombination mechanism, as it has been already observed during our work. In order to provide complementary information, another approach, which is called High-Frequency Modulated Photoluminescence (HF-MPL) can also be used to investigate carrier lifetime by using sinusoidal illumination variation and recording the phase shift between the excitation signal and emitted signal. We upgraded this method by extending the modulation frequency range up to 100 MHz, which is the fastest MPL setup to our knowledge and suitable for probing III-V materials. HF-MPL can provide different excitation conditions and enable to focus on slow mechanisms such as carrier trapping. Measurements have been performed on bulk InP as well as AlGaAs layers and GaAs photodiodes, showing carrier trapping features invisible to TRPL. Considering the complexity of the studied systems, we firstly focused on data interpretation for InP. Other III-V data are currently under study.

Authors : Avinash Kumar, Monika Agrawal, Amartya Chowdhury
Affiliations : Centre for Energy and Environment, MNIT-Jaipur (Malaviya National Institute of Technology) J.L.N. Marg, Jaipur (India) -302 017

Resume : The electrical performance of the solar cell in an outdoor condition deteriorates due to various environmental factors and internal losses like parasitic absorption and carrier recombination. Among them, the only temperature can be reduced using active or passive cooling techniques. Due to the low heat transfer coefficient of EVA and Tedlar, the heat generated in the solar cell does not evacuate easily and that further raises the temperature of the solar module. Radiative cooling is one of the best approaches to cool down the solar cell temperature along with front and back surface convective heat transfer. With the modified double-layer ARC have properties to improve the current density and radiative emission in the range of 4-25µm wavelength. The current density of the solar cell has been improved by 1.9 % with respect to a single layer ARC (commercial) solar cell. The double-layer ARC has also improved the emissivity in the range of 4-25µm and that has reduced the temperature of the solar cell by 1-2 ºC. This temperature reduction also improves the performance of the solar cell. Due to the temperature reduction, the life of the commercial solar cell will improve.

Authors : Pablo Sanchez-Palencia, Gregorio García, Pablo Palacios, Perla Wahnón
Affiliations : ETSI Telecomunicación and Instituto de Energía Solar, Universidad Politécnica de Madrid; ETSI Telecomunicación and Instituto de Energía Solar, Universidad Politécnica de Madrid ETSI Aeronáutica y del Espacio and Instituto de Energía Solar, Universidad Politécnica de Madrid; ETSI Telecomunicación and Instituto de Energía Solar, Universidad Politécnica de Madrid.

Resume : The intermediate band solar cell stands as one of the most outstanding options to make launch the 3rd Generation of photovoltaics with improved efficiencies. High concentration doping with transition metals has been proposed previously as a useful method to obtain IB materials. Using the experience in this methodology, applied until now mainly in chalcogenides, the in some manner forgotten space of multinary nitrides is explored looking for the desired properties to favour the generation of an intermediate band. This way, the family of ternary nitrides with spinel structure and group 14 elements as cations has been selected as a promising set of materials to study in detail in search of that possibility. Specifically, Sn3Ge3N8 presents a very convenient electronic configuration with a direct gap of 2.1 eV centered in and a good charge carriers mobility. After a systematic screening of the effect of the different transition metals doping in the host structure, some of the final compounds, by means of a precise study using GW approximation, present huge improvement in their absorption features. The analysis of their absorption spectra, obtained with a BSE calculation which consider excitonic effects, shows high absorption rates below the gap energy, leading inequivocally to the IB configuration.

Authors : Ji Yeon Hyun 1), Soohyun Bae 1), Yoon Chung Nam 1), Dongkyun Kang 1), Sang-Won Lee 1), Yoonmook Kang 2), Hae-Seok Lee 2) and Donghwan Kim 1),2)
Affiliations : 1).Department of Materials Science and Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 02841, Korea 2).KU-KIST GREEN School (Graduate School of Energy and Environment), Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 02841, Korea

Resume : Al2O3/SiNx stack passivation layers are among the most popular layers used for commercial silicon solar cells. In particular, aluminum oxide has a high negative charge, while the SiNx film is known to supply hydrogen as well as impart antireflective properties. Although there are many experimental results that show that the passivation characteristics are lowered by using the stack passivation layer, the cause of the passivation is not yet understood. In this study, we investigated the passivation characteristics of Al2O3/SiNx stack layers. To identify the hydrogenation effect, we analyzed the hydrogen migration with atom probe tomography by comparing the pre-annealing and post-annealing treatments. For chemical passivation, capacitance-voltage measurements were used to confirm the negative fixed charge density due to heat treatment. Moreover, the field-effect passivation was understood by confirming changes in the Al2O3 structure using electron energy-loss spectroscopy.

Authors : A.S. Gudovskikh (1, 2), A.A. Maximova (1,2), A.V. Uvarov (1), I.A. Morozov(1), A.I. Baranov(1), D.A. Kudryashov(1), J. Alvarez (3), A.N. Fioretti (4), M. Boccard (4), S. Le Gall (3), J.-P. Kleider (3)
Affiliations : (1) St.Petersburg Academic University RAS (Alferov University), St. Petersburg, Russia; (2) St. Petersburg Electrotechnical University “LETI”, St. Petersburg, Russia; (3) GeePs, Group of electrical engineering - Paris, CNRS, CentraleSupélec, Univ. Paris-Sud, Université Paris-Saclay, Sorbonne Université, 91192 Gif-sur-Yvette Cedex, France; (4) EPFL – PV-lab, Institute of microengineering (IMT), Neuchâtel, Switzerland

Resume : Very high conversion efficiency is reached using the concept of selective contacts in silicon based heterojunction solar cells. These use a stack consisting of a very thin layer of undoped hydrogenated amorphous silicon (a-Si:H) ensuring a good chemical passivation of the surface of the c-Si, and a layer of doped a-Si:H, n-type or p-type, for contact selectivity to extract electrons or holes, respectively. A new path, based on phosphide-type materials deposited by a low temperature plasma technique is explored in this paper. Gallium (GaP) and boron (BP) phosphides have a band gap significantly larger than c-Si and even than a-Si:H, thus limiting the absorption of the solar spectrum in these layers, which augurs well for a gain on the short-circuit current compared to the use of a-Si:H. Preliminary work has shown that GaP can be highly n-type doped, and has a significant valence band offset with c-Si, making it an excellent candidate as a selective electron contact, without requiring an additional ITO layer. Similarly, BP could be p-type doped, thus providing a selective contact for the holes. Phosphide layers with a bandgap around 2 eV were successfully grown by PE-ALD and PE-CVD processes. The material and heterojunction properties will be analyzed by combining several types of characterization techniques together with modeling studies.

Authors : Baranov, A.I.*(1,2), Kudryashov, D.A.(1), Morozov, I.A.(1), Uvarov, A.V.(1), Gudovskikh, A.S.(1,2)
Affiliations : (1) Alferov University, Russia. (2) St Petersburg Electrotechnical University "LETI", Russia. * lead presenter

Resume : Multi-junction solar cells (MJ SC) on silicon wafers are very perspective concepts for terrestrial applications since it combines suggested high efficiency and low cost of wafer. Method of plasma deposition (like PECVD) is much more suitable for industry than modern epitaxial ones, and, recently, layers of GaP were deposited by adopted approach of atomic-layer deposition (PE-ALD) on Si wafer. Furthermore, multilayer GaP/Si nanoheterostructures with Si quantum wells were obtained by PE-ALD for active layers in top subcells of MJ SC [1]. Here, electrophysical properties of GaP/Si multilayer structures grown on n-GaP wafers by PE-ALD with step of argon plasma activation are studied. Firstly, capacitance-voltage measurement confirmed possibility to profile the charge carrier density in silicon quantum wells in GaP/Si multilayer structures. Further, different defect levels were detected by deep-level transient spectroscopy. In result, hole trap with Ea=0.18 eV are formed in depth of 20-30 nm from the wafer surface after PE-ALD process due to argon treatment, but no responses observed deeper in GaP wafer. Then, three types of defects were detected in GaP/Si multilayer structures: (i) complex of SiGa+Pi, (ii) extended ones associated with levels in bandgap of GaP layers grown by PE-ALD, and (iii) responses at temperature higher 300 K related to defect with higher activation energy. [1] A.S. Gudovskikh et al. Materials Today: Proceedings 19 (2019) 47-52

Authors : Jung-hwa Lee(1) , Jun-hee Cho, Seunghun Baek, Doo-Hyun Ko*(1)
Affiliations : (1) Department of Applied Chemistry, Kyung Hee University, Korea

Resume : When light transmits into the solar cell, reflection occurs at the interface between air and an absorptive medium lowers solar cell efficiency. In this study, we present micro-dome structured anti-reflection (AR) films fabricated via simple imprinting technique. The functionality of the film in photovoltaic devices is evaluated, revealing reduced reflection caused by gradient refractive index effect and omnidirectional antireflection behavior, which lead to enhance the photovoltaic performance under both outdoor and indoor lighting. In addition, the AR film does not require any manipulation of solar cells as using a simple strategy of attaching the film on the surface, and its hydrophobic property affords self-cleaning effect, which should be beneficial for building integrated photovoltaics. Combined with these properties, our detachable AR films provide a practical guideline to boost solar cell performance.

Authors : Zhirong Yao, Weiyuan Duan, Jürgen Hüpkes, Andreas Lambertz, Annabel Mikosch, Hildegard Siekmann, Manuel Pomaska, Karsten Bittkau, Hui Shen, Kaining Ding
Affiliations : Zhirong Yao, Weiyuan Duan, Jürgen Hüpkes, Andreas Lambertz, Annabel Mikosch, Hildegard Siekmann, Manuel Pomaska, Karsten Bittkau, Kaining Ding IEK-5 Photovoltaik, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany; Zhirong Yao, Hui Shen Institute for Solar Energy Systems, Guangdong Provincial Key Laboratory of Photovoltaic Technology, School of Physics, Sun Yet-sen University, 510275 Guangzhou, PR China

Resume : Aim and approach: High efficiency silicon heterojunction (SHJ) solar cells require well-performing transparent (TCO) contact materials. To be suitable as antireflection and carrier transportation layer, the material must exhibit very low absorption and sufficiently high conductivity at the same time. In this work, we aim at optimizing optoelectronic properties of direct current (DC) and radio frequency (RF) sputtered Titanium oxide doped Indium oxide (ITiO) with substrate temperatures ≤ 200 oC, and compare the difference between these two sputter methods in obtaining high quality ITiO films and the application into SHJ solar cells. Our study will be divided in two parts, one part is optimization of the sputtering process for high quality ITiO films on corning glass substrates; the other part is the application of sputtered ITiO on SHJ solar cells and investigating the influence of the sputter conditions on the cell performance. The contact resistance between ITiO layer and silicon thin films is especially studied. 100 nm-thick ITiO films are deposited on corning glass substrates and the varied process parameters are heater temperature, sputtering pressure, power density and Ar/O2 ratio. The influence of post annealing process is also taken into consideration. Transmittance and reflectance are measured by a Perkin Elmer LAMBDA 950 spectrophotometer. Carrier density and Hall mobility are characterized by Hall Effect measurements. For cell preparation, hydrogenated intrinsic amorphous silicon layers are deposited on both sides of 170 µm-thick n-type double side textured Czochralski wafers, followed by the deposition of n-type a-Si:H on the front and p-type a-Si:H layers on the rear side by plasma-enhanced chemical vapor deposition (PECVD). 70 nm-thick ITiO films are then deposited on both sides of the samples using the same sputtering conditions. In the end, Ag electrodes are screen printed on both sides of the cells. The cell aperture area is 3.6 cm2. Solar cell performances are characterized under standard test condition. Scientific innovation and relevance: ITiO is a high performance transparent conducting oxide because of the expectionally high carrier mobility > 60 cm²V-1s-1.[1] Previous studies have employed soft deposition methods for example RF sputtering, ultrasonic spray pyrolysis and high process temperatures to fabricate high mobility ITiO.[2][3][4] In the industrial fabrication of TCOs the most established deposition method is DC mode sputtering which is a hard deposition method because of the high kinetic energy of the sputtering species. So far, the influence of DC mode sputtering on the quality of ITiO films and the cell performance of SHJ solar cells has not been investigated. Our study aims at closing this gap and presents the first results on DC mode sputtered ITiO on SHJ solar cells. Additionally, we show that this material can be processed at low temperature (≤ 200 oC) and high throughput which are two beneficial factors for the industrial fabrication of high efficiency SHJ solar cells. Preliminary results and conclusions: The electrical and optical properties of RF sputtered ITiO using different deposition conditions are presented. The Hall mobility of ITiO increases with temperature and reaches its maximum value of 53.5 cm2V-1s-1 at a substrate temperature of 200 °C. The films processed at 200 °C have the lowest resistivity of 2.16 × 10-4 Ω ·cm. With increasing O2 concentration in the plasma, the carrier density in the ITiO films decrease. The absorption of the ITiO layers increases in the near infrared (NIR) range with decreasing O2 concentration and substrate temperature because the increased carrier density induces free carrier absorption. When we apply the optimized RF sputtered ITiO films on SHJ solar cells we see that higher O2 concentrations increase the current density and series resistance. This is because of the lower absorption in the NIR range and higher sheet resistance of the ITiO layers. In comparison to SHJ solar cells with Sn-doped Indium oxide (ITO), the standard TCO used in our R&D baseline at the moment, the solar cells with RF sputtered ITiO exhibit a higher fill factor of 82.7 % (81.8 % with ITO). In this study, the champion cell with RF sputtered ITiO reaches a conversion efficiency of 23.8%. The study on DC sputtered ITiO films is ongoing and solar cell results will be presented at the conference. In addition, we will compare the difference from DC and RF sputtered ITiO and discuss the observations. Acknowledgements: This work has been supported by the HEMF (Helmholtz Energy Materials Foundry) infrastructure funded by the Helmholtz Association (HGF) and Street project (No. DB001618). The author Zhirong Yao thanks for the financial support from China Scholarship Council (CSC, 201806380137). Reference [1] R. Hashimoto, Y. Abe, and T. Nakada, “High mobility titanium-doped In2O3 thin films prepared by sputtering/post-annealing technique,” Appl. Phys. Express, vol. 1, no. 1, p. 015002, 2008, doi: 10.1143/APEX.1.015002. [2] L. T. Yan, J. K. Rath, and R. E. I. Schropp, “Electrical properties of vacuum-annealed titanium-doped indium oxide films,” Appl. Surf. Sci., vol. 257, no. 22, pp. 9461–9465, 2011, doi: 10.1016/j.apsusc.2011.06.035. [3] L. T. Yan and R. E. I. Schropp, “Changes in the structural and electrical properties of vacuum post-annealed tungsten- and titanium-doped indium oxide films deposited by radio frequency magnetron sputtering,” Thin Solid Films, vol. 520, no. 6, pp. 2096–2101, 2012, doi: 10.1016/j.tsf.2011.08.060. [4] S. Panyata, S. Eitssayeam, G. Rujijanagul, T. Tunkasiri, S. Sirisoonthorn, and K. Pengpat, “Preparation of titanium-doped indium oxide films by ultrasonic spray pyrolysis method,” Ferroelectrics, vol. 454, no. 1, pp. 63–69, 2013, doi: 10.1080/00150193.2013.842791.

Authors : Jae-Min Shin, In-Hwan Ahn and Doo-Huyn Ko*
Affiliations : Department of Applied Chemistry, Kyung Hee University

Resume : The approach to adapt upconversion nanoparticles to plasmonic structures has been studied to improve their inherent low quantum efficiency. However, the metal-based plasmonic structures have limits in extending their applications since they are rigid and opaque. In this study, we demonstrate a plasmonic film composed of an array of microbeads, which provides transferability and flexibility as well as distinctive upconversion luminescence enhancement. Our proposed structure comprises plasmonic silver nanoparticle-decorated silica microbeads on the dielectric-metal substrate, thereby providing remarkable improvements in absorption efficiency of near-infrared (NIR) light, and emission of visible (Vis) light via resonance mode excitation. As a result, the observed upconversion luminescence intensity exhibited three-order enhancement compared to reference under low power excitation. In addition, transparency and wide viewing angle property of emitted light for our film further extend its applicability for various fields such as absorption enhancement of photovotaics through visible light conversion in NIR and attachable NIR detection film.

Authors : Dmitry Mitin; Alexey Bolshakov; Alexey Mozharov; Sergey Raudik; Vladimir Fedorov; Vladimir Neplokh; Pramod Rajanna; Albert Nasibulin; Ivan Mukhin
Affiliations : Saint Petersburg Academic University, Russia; Saint Petersburg Academic University, Russia; Saint Petersburg Academic University, Russia; Saint Petersburg Academic University, Russia; Saint Petersburg Academic University, Russia; Saint Petersburg Academic University, Russia; Skolkovo Institute of Science and Technology, Russia; Skolkovo Institute of Science and Technology, Russia; Saint Petersburg Academic University, Russia

Resume : Single walled carbon nanotubes (SWCNT) are characterized by high conductivity and transparency. In addition, SWCNT have a wide direct band gap, significant photoabsorption and high mobility of charge carriers contributing to their efficient transport. All of this makes SWCNT an ideal photovoltaic material compatible with GaAs planar semiconductor structures. So SWCNT can act as a good alternative to metal contacts in a GaAs-based solar cell (SC). The use of SWCNT can reduce ohmic losses and shading of the active region in the SC. This work is devoted to fabrication and characterization of a GaAs solar cell with a SWCNT top contact. The characteristics of a conventional solar cell with a metal contact grid and solar cell with SWCNT electrode were compared to demonstrate the benefits of a SWCNT based approach. The photoelectric properties of the solar were are studied by measuring the IV characteristics and external quantum efficiency. The contact between the SWCNT and SC was examined by means of the optical and electron beam induced current techniques. SC with SWCNT contact has shown slight increase in the short circuit current density from 16.9 to 17.9 mA/cm2 and the EQE leading to 0.9% efficiency rise compared to SC with the conventional metal grid contact. Demonstrated technology of SWCNT electrodes fabrication can be applied to a wide range of semiconductor photovoltaic devices, including flexible thin-film solar cells and solar cells based on nanowires.

Authors : Mahdi,Zamani- Simon, Escobar Steinvall- Elias, Zsolt Stutz- Rajrupa,Paul-Jean-Baptiste, Leran- Anna Fontcuberta i Morral
Affiliations : Laboratory of Semiconductor Materials

Resume : Thanks to the abundancy of zinc and phosphorous, zinc phosphide has great potential for large-scale thin film photovoltaics. In particular, it exhibits high carrier mobility, diffusion length, absorption coefficient, and furthermore, its direct bandgap of 1.5 eV is close to optimal value of the Shockley-Queisser limit. Separate source Molecular Beam Epitaxy (MBE) is an ideal platform for optimizing the growth of thin films as it provides precise control over the molecular/atomic fluxes and substrate temperature. Here, we present the growth of zinc phosphide thin films on InP(100) substrates. While there had been previous attempts to grow this material using compound and separate source MBE, none of them had been carried out of this substrate. We provide an overview of the thin film morphology and crystalline quality as a function of the zinc and phosphorous fluxes as well as V/II ratio. The temperature window resulting in high crystalline quality is assessed by X-ray diffraction, transmission electron microscopy (TEM) and Raman spectroscopy. The figure below provides an overview of a typical Raman spectrum of a high quality film. The observed peaks are analysed in terms of crystalline quality and crystalline texture. The functionality of the materials is further evaluated by photoluminescence (PL). This study provides information about the growth of zinc phosphide thin films that could be valuable for implementation of this material for photovoltaics applications.

Authors : Nicolae Spalatu, Robert Krautmann, Atanas Katerski, Erki Karber, Jaan Hiie, Ilona Oja Acik and Malle Krunks
Affiliations : Department of Materials and Environmental Technology, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia

Resume : The search for new semiconductor materials and the improvement of the existing materials represent a major focus for innovative photovoltaic applications and device integration. Doping is the usual approach for modifying and widening physical and chemical semiconductor properties, while multinary alloys allow for the simultaneous adjustment of both the band gap and lattice constant, allowing for an increase in a radiant efficiency at a broader range of wavelengths. In this study, a novel approach of deposition by close-spaced sublimation of thin-films of the Sb2Se3-SnS chalcogenide alloy is investigated. Sb2Se3-SnS thin films are obtained by in-situ addition of SnS into Sb2Se3 with concentration varying from 0.1 to 5 at%. SnS introduced p-type doping in Sb2Se3, decreases the resistivity, increases the dark-to-light resistance ration and enhances the carrier density. No evident changes in structure and morphology compared to Sb2Se3 films are observed. Sb2Se3-SnS films shows basic orthorhombic structure but with little variations in the lattice parameter and band gap are observed for high extent Sb2Se3-SnS alloying. Thin-film solar cells with Sb2Se3-SnS absorber are fabricated. Admittance spectroscopy and low-temperature photoluminescence measurements are used for defect studies and insights into the physico-chemistry of the material and devices are provided.

Authors : Camilo Chinchilla (1), Mikel Hurtado (1), Sara Cabrera (1).
Affiliations : (1) Central University, Colombia

Resume : This article presents the implementation of an automatic spray equipment for the creation of multilayer materials, which allow to growth materials for manufacturing Grätzel solar cells devices; uses of spray coating open atmosphere techniques causes different changes in physical and chemical thin film technology (TFT) properties mainly in morphology, mechanical, compositional, magnetic and optical ones, improving at the same time nanoparticle adhesion phenomena. Through the Conceive-Design-Implement-Operate or CDIO method, a system was designed to control spray type, movement, cycles, surrounding conditions and temperature sensing, and this device was developed to apply the most efficient coating technique when performing production TFT processes. Due to the development of this device were obtained significant results in the fabrication of solar cells using graphene-like material, TiO2, molecules for sensitizing semiconducting materials on substrate slides glass with accuracy thickness in the order of nm. Above materials were used to performed photovoltaic Grätzel cell devices and was found a maximum electrical potential between 120 mV and 520 mV, in a 7.0 cm2 on standard illumination conditions, these results depend of fabrication process and molecules used on.

18:30 AWARD CEREMONY followed by SOCIAL EVENT    
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09:45 Break    
Intermediate band, quantum dots and hot carrier solar cells : Laurent Lombez
Authors : Yoshitaka Okada
Affiliations : University of Tokyo, Research Center for Advanced Science and Technology (RCAST), Japan

Resume : Significant efforts are made with quantum dot intermediate band solar cells (QD-IBSCs) for achieving high conversion efficiency [1]. Presently, research on QD-IBSCs is continuing in three areas. The first is to establish method to fabricate high-density QDs array of low defect density and with long radiative recombination lifetimes. The areal density of QDs has direct influence on the generation and recombination processes via IB states and for this, we have shown that strain-compensated growth improves the QDs quality and InAs/GaAs QDSC characteristics with QD stacks up to 100 layers in self-organized heteroepitaxy by MBE [1]. However, the average QD size prepared by such dry method is still large and in-plane density is low, typically limited to the range of 15-30 nm and 1e11-1e12 cm/2, respectively. To this end, optimized QD-IBSC structure prepared by a solution process in which PbS colloidal QDs of 4 nm in size were densely dispersed in a bulk perovskite matrix with a high energy bandgap of 2.4eV has been studied [2]. The second challenge is to increase the carrier lifetime in IB states by controlling the recombination rates such as by using type-II QD heterostructure or superlattice that allows fast spatial separation of carriers, and a photon-ratchet approach. Lastly, maximizing the photocurrent generation by 2-step photoabsorption (TSPA) by optimally doping the QDs to realize partially-filled IB states is important to improve the current matching between valence band (VB)-IB and IB-conduction band (CB) current production paths. [1] Y. Okada et al, Appl. Phys. Rev. 2, 021302 (2015). [2] H. Hosokawa et al, Nature Commun. 10, 43 (2019).

Authors : Tanja Jawinski, Michael Lorenz, Roland Scheer, Marius Grundmann, Holger von Wenckstern
Affiliations : Tanja Jawinski Universität Leipzig, Felix-Bloch-Institut für Festkörperphysik, Germany; Michael Lorenz Universität Leipzig, Felix-Bloch-Institut für Festkörperphysik, Germany; Roland Scheer Martin-Luther-Universität Halle-Wittenberg, Institut für Physik, Germany; Marius Grundmann Universität Leipzig, Felix-Bloch-Institut für Festkörperphysik, Germany; Holger von Wenckstern Universität Leipzig, Felix-Bloch-Institut für Festkörperphysik, Germany

Resume : To overcome the Shockley Queisser limit of single junction solar cells (SC), an intermediate band (IB) can be introduced between the valence band (VB) and the conduction band (CB) of a wide band gap material [1]. Thus, sub-bandgap photons can be absorbed by VB to IB and IB to CB transitions. Furthermore, thermalization losses can be reduced due to the higher band gap compared to single junction SC. A promising material to realize such an IBSC is In2S3 hyperdoped with Vanadium [2]. We use physical co-evaporation of the elements as a combinatorial approach to grow In2S3:V layers with up to 14 at% V. To initiate epitaxial growth we use p-Si wafers as substrates. As transparent top electrode n-ZnO:Al grown by pulsed laser deposition is used to realize heterostructure pin-SC. Reference SC without IB are prepared using undoped In2S3. Investigations of structural properties reveal epitaxial growth even for V-doped samples. We find high rectifications of up to almost 6 orders of magnitude by current-voltage characteristics in the dark. Measurements under illumination reveal no increase in the short circuit current density for V-doped samples, which indicates that the IB is full, in agreement with [3]. We investigate defect states that are induced by Vanadium using thermal admittance spectroscopy, to determine the energetic position of the IB. [1] Luque and Martí, Phys. Rev. Lett., 1997, 78. [2] Palacios et al., Phys. Rev. Lett., 2008, 101. [3] Ghorbani et al., J. Mater. Chem. A, 2019, 7.

Authors : Julien Marquardt, Sergej Levcenco, Alexandra Franz, Thomas Unold, Christiane Stephan-Scherb, Susan Schorr
Affiliations : Helmholtz-Zentrum Berlin for Materials and Energy, Germany; Helmholtz-Zentrum Berlin for Materials and Energ, Germany; Helmholtz-Zentrum Berlin for Materials and Energy, Germany; Helmholtz-Zentrum Berlin for Materials and Energy, Germany; Bundesanstalt für Materialforschung und –prüfung (BAM), Germany; Helmholtz-Zentrum Berlin for Materials and Energy, Germany, Freie Universitaet Berlin, Germany

Resume : Intermediate band solar absorber materials based on well-known chalcopyrite type semiconductors can be a low cost and efficient alternative in solar energy production [1]. A comprehensive analysis of the structural incorporation of manganese in the wide band gap CuGaS2 chalcopyrite type semiconductor is demonstrated by means of X-ray diffraction, neutron diffraction and photoluminescence spectroscopy. In this systematic study powder samples were prepared by solid state reaction of pure elements, following the pseudo-binary section of CuGa1-xMnxS2 and (CuGaS2)1-x(2MnS)x, respectively. The alloyed ternary phase consequently crystallizes in the chalcopyrite type structure with a maximum manganese content of 0.091 mol-%. It is shown that the actual incorporation of manganese follows rather the pseudo-binary section of a coupled substitution ((CuGaS2)1-x(2MnS)x) than of a unilateral substitution (CuGa1-xMnXS2) independent of their initial composition [2]. The increasing manganese content results in a continuous increase of the lattice parameters a and c, as respective marker for the incorporation into the crystal structure. From analysis of the average neutron scattering length of the cation sites a manganese incorporation is observed for both cation sites of the chalcopyrite host phase. The occurring extrinsic and intrinsic point defects,deduced from neutron diffraction data, were related to the photoluminescence spectra and correlated with the predictions given by density functional theory (DFT) [3]. [1] Marti et al., JAP 103, 073706 (2008) [2] Marquardt et al. Phys. Stat. Sol. A (2019) 1800882 [3] Zhao & Zunger, Phys. Rev. B 69 (2004)

Authors : Xiaolei Chu (a), Hamed Heidari (a), Alex Abelson (b), Davis Unruh (c), Chase Hansen (c), Caroline Y. Qian (b), Gergely Zimanyi (c), Matt Law (b), Adam J. Moule (a)
Affiliations : (a) University of California, Davis - Department of Chemical Engineering (b) University of California, Irvine - Departments of Chemistry and Materials Science (c) University of California, Davis - Department of Physics

Resume : Epitaxially-fused colloidal quantum dot (QD) superlattices (SL) promise to combine the unique photophysics of QDs with the efficient band transport of bulk-semiconductors. PbS and PbSe QD layers have demonstrated multiple exciton generation in response to photo excitation by high energy photons. However, devices made from epi-QDSL samples fail to demonstrate superior PV characteristics due to poor superlattice order. We would like to extend the multi-exciton generation to thick arrays of QDs, which is possible if the structural order of the film is improved to reduce electronic traps. We fabricate extended superlattice films with multi-layers of QDs and examine how the solution assembly fabrication method affects the QD structural and electronic local order. Specifically, we form ordered arrays of PbSe QDs at a liquid-liquid interface and then reduce the spacing between QDs using in-situ ligand exchange. The resulting films are characterized using high-resolution scanning transition electron tomography (STET). We are able to resolve the position of each QD in a sample encompassing 1846 QDs. In addition of the particle positions, we also resolve the presence (or lack of) of epitaxial connections between neighboring QDs and the thickness of the neck formed between neighboring QDs. We also examine a SL grain boundary and show the presence of necking across the grain boundary in spite of poor crystalline alignment between Qds. This morphological information is used to generate an electronic transport model. Our model shows that the energetic disorder caused by heterogeneous epitaxial bridging between QDs in a single domains is about one order of magnitude less important than the presence of disorder at grain boundaries between superlattice domains. This presentation will explore the link between structural and electronic order in these complex 3D samples.

Authors : E. Marino, T. Kodger, F. Messina, F. Koenderink, and P. Schall
Affiliations : Van der Waals-Zeeman Institute, University of Amsterdam, Amsterdam, The Netherlands; Physical Chemistry and Soft Matter, Wageningen University, Wageningen, The Netherlands; Dipartimento di Fisica e Chimica, Universita degli Studi di Palermo, Palermo, Italy; Center for Nanophotonics, AMOLF, Amsterdam, The Netherlands; Van der Waals-Zeeman Institute, University of Amsterdam, Amsterdam, The Netherlands

Resume : The assembly of colloidal quantum dots (QDs) into dense superstructures holds great promise for novel optoelectronic devices. The rich and unique photophysics of QDs can benefit solar cells by harvesting hot carriers, thereby decreasing thermalization losses and significantly raising the maximum power conversion efficiency. However, the working principles of these devices rely on efficient light absorption and charge carrier transport, which are both limited for quantum dots and their aggregates. A recently developed emulsion-templated assembly technique yields QD supercrystals of extraordinary structural quality, expected to feature `artificial solids' with properties beneficial for PV devices. Here, we show that these supercrystals simultaneously enhance the absorption efficiency and inter-dot coupling of QDs. By comparing optical measurements with Mie theory, we demonstrate that supercrystals can exhibit resonant optical properties resulting in absorption efficiencies greater than 1 in the visible range. By performing ligand exchange, we increase the excitonic coupling, and show via ultrafast transient absorption (TA) spectroscopy that biexcitons transits from a bound to a free state as a consequence of the increased interdot coupling. These results reveal a new state of matter with properties architecturally designed to feature simultaneously photonically and electronically coupled QDs for future optoelectronic devices.

Authors : Andreas Pusch, Milos Dubajic, Michael P. Nielsen, Stephen P. Bremner, Gavin J. Conibeer, Nicholas J. Ekins-Daukes
Affiliations : School of Photovoltaic & Renewable Engineering, UNSW Sydney, Kensington 2052, Australia

Resume : Hot carrier solar cells promise high solar energy conversion efficiencies far beyond the Shockley-Queisser limit, yet no practical improvements have been achieved. Opto-electronic reciprocity relations have proven very useful in improving the efficiency of single junction solar cells. Here, we derive opto-electronic reciprocity relations for hot carrier cells by analysing their behaviour in the dark. We find wildly differing predictions by using the two prevalent models for hot carrier solar cells, namely the particle conservation model with a finite quasi-Fermi level separation in the absorber and the purely thermal carrier model. Assuming ideally energy selective contacts, a purely thermal electron distribution in the absorber results in a temperature of the absorber that is defined by the ratio between applied bias and contact energy, independent of cooling rates. The dark I-V does not resemble a diode. In contrast, the particle conservation model predicts that the temperature in the absorber depends on the cooling rate and contact energy and is independent of applied bias in a large bias regime. The applied bias changes the quasi-Fermi level separation in the absorber resulting in diode-like behaviour. The reciprocity relations relate the magnitude of the current to the cooling rate in case of thermal carrier distributions and the temperature as function of bias in case of carrier distributions that follow the particle conservation model.

12:00 LUNCH    
Novel photovoltaic absorbers (II) : Yoshitaka Okada
Authors : Reuben Collins, Yinan Liu, William Schenken, Craig Taylor, Lakshmi Krishna, Carolyn Koh
Affiliations : Colorado School of Mines

Resume : Si clathrates are cage-like, crystalline Si inclusion compounds with potentially interesting optical and electronic properties. Typically, Na in clathrates is viewed as the interstitial guest. However, if the Na content is low enough, Si clathrate can become a semiconductor with Na as a dopant. Here we report an EPR study of Type II Si clathrate prepared with low Na concentration, which provides new insights into the properties of this cage-like Si allotrope and into Na as an n-type dopant. An EPR line arising from unterminated Si bonds in a disordered Si phase is identified in the system. The presence of this amorphous-like component helps explain the thermally activated hopping-related conductivity that has long been observed, but which is poorly understood. This study also identifies “super-hyperfine” lines surrounding each Na hyperfine line due to interactions of the donor electron with a Si29 nucleus on the cage and confirms the identification of hyperfine lines due to interactions of two or more neighboring Na nuclei. Analysis of the strength of these interactions shows nearly half of the electron wavefunction associated with the Na donor extends onto surrounding cages consistent with the identification of Na as a shallow donor and provides quantitative evidence of Na clustering. These results help to resolve outstanding questions about electron transport in Si clathrates and reinforce that Si clathrates could become an alternative n-type semiconductor.

Authors : Zewei Li,1 Sachin Dev Verma,1 Akshay Rao,1 Richard H. Friend1 and Robert L. Z. Hoye2
Affiliations : 1 Cavendish Laboratory, University of Cambridge, JJ Thomson Ave, Cambridge CB3 0HE, UK; 2 Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ, UK

Resume : There is current interest in finding non-toxic alternatives to lead-halide perovskites for optoelectronic applications. Silver-bismuth double perovskites (e.g., Cs2AgBiBr6) have recently gained attention because they maintain the perovskite crystal structure, whilst substituting the toxic lead cation for the more benign silver and bismuth cations. Recently, we showed that Cs2AgBiBr6 exhibits a long charge-carrier lifetime of 1.4 microseconds, which can sustain a large steady-state excess carrier density under 1 sun illumination.[1] However, the indirect band gap exceeds 2 eV and is too wide for single-junction or multi-junction photovoltaic applications. Recent literature suggests that alloying the Bi3+ cation with Sb3+ can lower the band gap. This talk examines the potential and challenges of this approach when realised in solution-processed thin films. The ratio of Sb:Bi is varied over the entire composition range in solution, and the effect on the bulk and surface composition of the thin films measured, along with the effect on the phase-purity and charge-carrier lifetime, measured by transient absorption spectroscopy. Band gap bowing is observed (i.e., the smallest band gap is obtained using a mixed Sb-Bi alloy) and the origin of this effect examined. A route to growing pinhole-free thin films is developed, and the effect of Sb content on the performance of the double perovskites in photovoltaic devices examined. [1] Robert L. Z. Hoye, et al., Adv. Mater. Interfaces, 2018, 5, 1800464

Authors : M. Khuili
Affiliations : (1) Superior School of Technology (EST-Khenifra), University of Sultan Moulay Slimane, PB 170, Khenifra 54000 Morocco. (2) Laboratory of Materials Physics, Faculty of Sciences and Technologies, B.P 523, 23000 Beni Mellal, Morocco.

Resume : The volatility of organic cations in hybrid perovskites based on lead (Pb), and the possibility of lead contamination are the two main subjects of concern in the manufacture of optoelectronic devices based on this type of perovskites. A promising new family of hybrid metal halide perovskites based on Titanium Cs2TiX6 (X = Cl, Br) non-toxic, abundant in earth will be an alternative to these lead (Pb)-based perovskites. In this article, we have performed calculations to reveal the optoelectronic and transport properties for this new material. The results of the calculations are in good agreement with the experimental ones available. The Gap energy calculated in the case of Cs2TiCl6 is reduced when "Cl" is replaced by "Br". Studies of optical absorption spectra carried out in the energy range from 0 to 5 eV, confirm the efficient use of these compounds in solar cells and other optoelectronic applications. In addition, calculations of transport properties made using the semi-classical Boltzmann theory show thermoelectric power near the ambient temperature range, which admits the possible use of these compounds as thermoelectric materials at low temperature.

Authors : George Volonakis, Feliciano Giustino
Affiliations : Institut des Sciences Chimiques Rennes, Université Rennes 1 FR, Department of Materials, University of Oxford, UK; Oden Institute for Computational Engineering and Sciences, The University of Texas at Austin, USA, Department of Materials, University of Oxford, UK

Resume : Recent computational design strategies towards designing new materials that do not contain Pb have been remarkably successful, and lead to the discovery of a series of novel compounds within the so-called halide double perovskites family. [1] Today there are five inorganic crystals that have been synthesized and characterized; Cs2BiAgCl6, Cs2BiAgBr6, Cs2SbAgCl6, Cs2SbAgBr6, and Cs2InAgCl6. Among these, Cs2BiAgBr6 has the narrower indirect band gap of 1.9 eV, and Cs2InAgCl6 is the only direct band gap semiconductor, yet with a large gap of 3.3 eV. All of them exhibit low carrier effective masses and consequently, are prominent candidates for opto-electronic applications including photovoltaics. Here, we probe oxide perovskites to look for potential promising oxide perovskites following our substitution-based computational design approach. We identify a new oxide double perovskite semiconductor: Ba2AgIO6 (BAIO), and report on its synthesis by low-temp solution process. BAIO has a band gap in the visible range (i.e. 1.9 eV), and a broad PL spectrum. Surprisingly, BAIO has an electronic band structure remarkably similar to that of our recently discovered perovskite Cs2AgInCl6. This allows us to further develop a universal analogy concept that can be used to identify links between oxide and halide perovskites. As such example, we show how BAIO and Cs2AgInCl6 are both analogs of the well-known transparent conductor BaSnO3, but the significantly lower band-gap of BAIO makes this new compound more promising for oxide-based optoelectronics and for novel monolithic halide/oxide devices. [1] Patent WO 2017/037448 Al (2015); JPCL 7 1254 (2016); JPCL 8 772 (2017); APL 112 243901 (2018) [2] JPCL 8 3917 (2017) [3] Patent Application 19386013.7 (2019) ; JPCL 10 1722 (2019)

Light management : Yoshitaka Okada
Authors : Hu, J.(1), Pérez, L.A.*(1), Alonso, M.I.(1), Garriga, M.(1), García-Pomar, J.L.(1), Mihi, A.(1) & Goñi, A.R(1,2).
Affiliations : (1) Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, 08193 Bellaterra, Spain. (2) ICREA, Passeig Lluís Companys 23, 08010 Barcelona, Spain

Resume : The worldwide energy demand fosters the development of new strategies to improve energy conversion efficiencies in photovoltaic devices. The alternative we propose in this work is to achieve thermionic emission of electrons in a solid-state, cold-cathode device by the absorption of infrared (IR) photons in the unused region of the solar spectrum using plasmonic nanostructures patterned on the cathode. The plasmons launched by the absorption of the IR photons generate, upon fast relaxation, a photocurrent in the semiconductor. As a proof of concept, arrays of inverted Au-coated pyramids were etched over areas of 1 square centimeter of a silicon substrate using wet chemical methods, having lateral sizes of 1-4 microns and periods of 2-7 microns. The optical properties were characterized using Fourier-transform infrared spectroscopy (FTIR). Multiple absorption bands associated with different plasmon resonances were observed in the desired spectral range, which were tuned in frequency and amplitude by modifying the structural parameters of the array. Finite-difference time-domain (FDTD) methods were used for the design optimization of the fabricated arrays regarding their optical properties. In particular, we aimed at maximizing the electromagnetic field enhancements obtained at the plasmon resonance frequencies to boost electron emission from the cold cathode. Selected structures will be implemented in a proper thermionic device and evaluated measuring the produced photocurrents.

Authors : Ankit Chauhan1, Gil Shalev1,2
Affiliations : 1. School of Electrical & Computer Engineering, Ben-Gurion University of the Negev, POB 653, Beer-Sheva 8410501, Israel; 2.The Ilse-Katz Institute for Nanoscale Science & Technology, Ben-Gurion University of the Negev, POB 653, Beer-Sheva 8410501, Israel.

Resume : Arrays of subwavelength dielectric structures has recently proved an important research venue towards the realization of thin film photovoltaics. In the following I introduce a new paradigm towards efficient light trapping and the broadband absorption of the solar radiation based on silicon surface arrays composed of subwavelength trumpet non-imaging light concentrators (trumpet arrays)1. In geometrical optics, a three-dimensional trumpet non-imaging light concentrator is a hyperboloid of revolution with an ideal light concentration ratio. We use finite-difference time-domain electromagnetic calculations to study the optical response of an infinite cubic-tiled substrate-less silicon trumpet array under normal illumination. We show that the absorptivity spectra of trumpet arrays are characterized by strong absorption peaks, some of which are just below the Yablonovitch limit. The improved light trapping is attributed solely to efficient occupation of the array Mie modes, and we show absorption improvement at the near infrared that is an order of magnitude higher than that of optimized nanopillar (NP) arrays. We show an enhanced broadband absorption of the solar radiation in trumpet arrays compared with that of optimized NP arrays (~26% enhancement). The superior optical absorption in trumpet arrays is governed by low transmissivity, in contrast with NP array in which the absorption is governed by low reflectivity. Finally, we show that low reflectivity in trumpet arrays is governed by modal excitations at the upper part of the trumpets (which is also supported by the weak dependency of the reflectivity on the array height), whereas the transmissivity is governed by modal excitations at the lower part of the trumpets. References (1) Prajapati, A*.; Chauhan, A*.; Keizman, D.; Shalev, G. Approaching the Yablonovitch Limit with Free-Floating Arrays of Subwavelength Trumpet. Nanoscale 2019.

Authors : Daniel M. Kroupa, Matthew J. Crane, Daniel R. Gamelin
Affiliations : BlueDot Photonics, University of Washington; BlueDot Photonics, University of Washington; BlueDot Photonics, University of Washington

Resume : Recent advances in lanthanide doping of CsPbX3 (X = Cl, Br, I) perovskites have opened new opportunities for their application as spectral conversion phosphors. This talk will describe recent research into understanding and controlling the photophysical process of quantum-cutting in ytterbium-doped CsPb(Cl1-xBrx)3 for photon management in solar spectral-conversion applications. A combination of variable-temperature and time-resolved spectroscopy provide insight into the quantum-cutting process that produces remarkably high photoluminescence quantum yields in these materials (>100%). The application of these materials for solar photon management in next-generation photovoltaics will also be described.

16:00 Break    
Authors : D. G. Congrave, B. H. Drummond, V. Gray, D. Credgington, A. Rao, H. Bronstein
Affiliations : Department of Chemistry, University of Cambridge, United Kingdom Cavendish Laboratory, University of Cambridge, United Kingdom

Resume : Anthracene derivatives are classic and unique luminophores which combine high photoluminescence quantum yields (PLQY), large exchange energies (ΔEST) and narrow Stokes shifts. This makes them ubiquitous in many applications, particularly organic light emitting diodes and triplet-triplet annihilation upconversion (TTAUC). Anthracenes should, therefore, be highly valuable building blocks for luminescent conjugated polymers, particularly if TTA is desired. Unfortunately this has been thwarted by the extended π system of anthracene which imparts a strong tendency for it to aggregate. This firstly suppresses materials solubility, restricting molecular weight and processability. Secondly, aggregation prompts photodimerisation,1 aggregation caused quenching (ACQ)2 and the formation of excimers in the solid state.3 These constitute PL quenching pathways and their exact extent is hard to predict and must be controlled. We have surmounted aggregation through molecular encapsulation to develop true conjugated anthracene polymers with high molecular weights and minimal ACQ which do not form excimers. These materials provide a new lease of life for an established luminophore and are ideal annihilators towards single material solid state TTAUC films. Results for this unprecedented application will be presented. 1 Zhu, L. et al., J. Am. Chem. Soc. 2011, 133, 12569–12575. 2 Egbe, D. A. M. et al., Macromolecules 2010, 43, 1261–1269. 3 Freeman, D. M. E. et al., Polym. Chem. 2016, 7, 722–730.

Advanced characterisations and concepts : Robert Hoye
Authors : Laurent Lombez,1,3, Hamidreza Esmaielpour,1, Soline Boyer-Richard,4, Alain Le Corre,4, Alexandre Beck,4, Olivier Durand,4, Julie Goffard,5, Amaury Delamarre,5, Stéphane Collin,5, Andrea Cattoni,5, Daniel Suchet,1,2,3, Jean-François Guillemoles,1,3
Affiliations : 1 Institut Photovoltaique d’Ile de France (IPVF), 18 boulevard Thomas Gobert, Palaiseau, France; 2 CNRS, Ecole Polytechnique, Institut Photovoltaïque d’Ile-de-France UMR 9006, 18 boulevard Thomas Gobert, 91120, Palaiseau, France; 3 CNRS-Institut Photovoltaique d’Ile de France (IPVF), UMR 9006, 18 boulevard Thomas Gobert, Palaiseau, France; 4 Univ Rennes, INSA Rennes, CNRS, Institut FOTON – UMR 6082, Rennes, France; 5Centre de Nanosciences et de Nanotechnologies (C2N), CNRS, Université Paris-Saclay, 10 boulevard Thomas Gobert, 91120 Palaiseau, France;

Resume : The development of advanced photovoltaic concepts that might overcome the single junction efficiency limit, as well as the development of new materials, rely on advanced characterization methods. Among all the methods the optical ones are very well adapted to quantitatively probe optoelectronic properties at any stage. We here present the use of multidimensional imaging techniques that record spectrally and time resolved luminescence images. As a typical example, we show how to harvest the available solar energy using hot carrier devices and evidence a positive contribution of the hot carrier effect on the photovoltaic performances. We can extract temperature and quasi-Fermi level splitting (internal voltage) of photo-generated carriers at various lattice temperatures and excitation powers. The device might be seen as a combination of photovoltaic and thermoelectric device and the outputs of the optical method impact both communities. The reduce thermalization mechanisms seems to positively impact PV performances of our multi-quantum well devices. To go further, we show how to obtain individual temperatures of electrons and holes from spectral analysis. The individual thermalization coefficients of each carrier as well as the individual Seebeck coefficients are also determined. This quantitative thermodynamic study also help to develop the conception of other PV devices. Finally, the optical method favors the design of nanostructures to increase the light absorption in very thin layers. It therefore boosts PV performances by enhancing physical mechanisms such as the hot carrier effect.

Authors : Bruno Lorenzi, Dario Narducci
Affiliations : Dept. of Materials Science, University of Milano Bicocca, via R. Cozzi 55, 20125 Milan, Italy

Resume : Silicon solar cells dominate the photovoltaic (PV) market. Their high efficiencies, along with their relatively low cost, make them the most valuable solution nowadays. However, it is well known that silicon solar cells are extremely sensitive to temperature, and they can lose up to 15 – 20% of their room temperature efficiency under normal operating conditions. In this perspective, less sensitive solar cells such as amorphous silicon (a-Si), Gallium Indium Phosphide (GaInP), and Perovskites, have been proposed as valuable alternative solutions. However, the room temperature efficiencies of these candidate materials are still lower than those of silicon devices, making them not competitive enough. Hybrid Thermoelectric-Photovoltaic (HTEPV) systems, which recover solar cell heat losses to produce an additional power output, are a suitable option to enhance the competitiveness of these kind of solar cells. In this communication we report on the development and the characterization of bismuth telluride thermoelectric generators with a layout optimized to hybridize aSi, GaInP or Perovskites solar cells. The results showed in all three cases, efficiency enhancements up to 3.5% depending on the solar cell and on the irradiation level. Efficiency improvements are in excellent accordance with theoretical estimations. For Perovskites solar cells the efficiency of the hybrid device was found to be higher than that of typical silicon solar cells. This experimental evaluation demonstrated in an accurate fashion the real potential of thermoelectric hybridization of solar cells.

Authors : Romaric de Lépinau 1,2, Capucine Tong 1,2, Hao Xu 3,4, Thomas Bidaud 2, Amaury Delamarre 2,4, Fabrice Oehler 2, Andrea Scaccabarozzi 2, Stéphane Collin 2, Andrea Cattoni 2
Affiliations : 1- IPVF, Institut Photovoltaïque d’Île-de-France, 91120 Palaiseau, France; 2- C2N, Centre de Nanosciences et de Nanotechnologies, 91120 Palaiseau, France; 3- RCAST, University of Tokyo, Tokyo, Japan; NextPV; 4- LIA CNRS-University of Tokyo–University of Bordeaux

Resume : Nanowires (NW) are a potential solution to grow III-V material on silicon (Si) without lattice-mismatch issues, and thus represent an attractive technology to fabricate high-efficiency III-V/Si tandem solar cells and overcome the efficiency limit of the mainstream Si technology. Fabricating NW solar cells presents several challenges: growing organized arrays of NWs with high optoelectronic quality, processing NW arrays into devices, and characterising those devices (consisting of up to 10^9cm-2 sub-µm sized junction in parallel). GaAs NW solar cells have been fabricated on patterned Si substrates by MBE. Our innovative core-shell heterostructure design consists in a p-GaAs core grown using the VLS method, and a n-GaInP high-bandgap shell. For fabricating complete devices, the NWs are encapsulated in a polymer, and contacted by a transparent conductive oxide. Our best sample has a 3.7% conversion efficiency, with a Voc = 0.66V, which is above the current record for GaAs NW solar-cells on silicon. To assess the intrinsic quality of the NWs, we have used a hyperspectral imager to determine without contact the quasi-Fermi level splitting in unprocessed samples. Under a 1 sun illumination, we find values up to 0.93eV, representing the maximum achievable Voc. It confirms the NWs high crystalline quality, and indicates a considerable scope for improvement in device processing. These results will be presented combined with in-progress cathodoluminescence measurements of single NWs.

Authors : Pascal Kaienburg, Uwe Rau, Moritz Riede, Thomas Kirchartz
Affiliations : Clarendon Laboratory, Department of Physics,University of Oxford, Oxford (UK) and IEK-5: Photovoltaics, Forschungszentrum Jülich, Jülich (Germany); IEK-5: Photovoltaics, Forschungszentrum Jülich, Jülich (Germany); Clarendon Laboratory, Department of Physics,University of Oxford, Oxford (UK); IEK-5: Photovoltaics, Forschungszentrum Jülich, Jülich (Germany) and Faculty of Engineering and CENIDE, University of Duisburg-Essen, Duisburg (Germany)

Resume : The efficiency potential of any solar cell absorber material is largely determined by three material parameters – the absorption coefficient α, charge carrier mobility μ and charge carrier lifetime τ. While the relevance of each parameter is unquestioned, their relative importance is not self-evident. One could ask for example, whether a tenfold increase in mobility or absorption coefficient is more beneficial in terms of solar cell performance. With parameter values varying over several orders of magnitude, such questions are of great practical relevance for emerging inorganic and organic solar cells. Here we present how α, μ and τ quantitatively affect solar cell efficiency. By performing numerical drift-diffusion simulations over a wide representative parameter space, we find different efficiency-(αμτ) relations for different mobility regimes. We find no fundamental difference between simulations based on monomolecular and bimolecular recombination, representative of inorganic and organic solar cells, respectively. Special attention is given to the impact of surface recombination, which may present an ultimate limit to solar cell efficiency. With a focus on organic solar cells, we assess the gain in efficiency obtained from an increase in absorption strength. As many organic absorber blends suffer from modest mobilities and recombination coefficients, we conclude that designing molecules with enhanced absorption strength are a path to overcome today’s efficiency limits.


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Symposium organizers

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Marin ALEXEUniversity of Warwick

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Mutsumi SUGIYAMATokyo University of Science

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Thomas FIX (Main)ICube laboratory, CNRS and University of Strasbourg

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