Materials and devices for energy and environment applicationsR
Organic solar cells including polymers, dyes or perovskites
Introduction and scope:
During the last ten years, great attention has been devoted to organic solar cells including polymeric, dye or quantum dot sensitized and perovskite solar cells, as well as hybrid devices including polymers and nanomaterials such as graphene, CNTs, oxides, metal or semiconducting nanoparticles.
The use of the organic materials is assumed to be very promising in photovoltaic (PV) devices in comparison with inorganic based solar cells because the possibility of lowering costs due to roll-to-roll production techniques, the fabrication of flexible, wearable, lighter devices; the use of semitransparent cells integrated to architecture with bifacial absorption as well as a better disposability at the end of its duty life.
Presently, organic solar cells are widely investigated in some main directions:
- modification of active layer by applying new polymers, copolymers or small compounds as donor, or donor-acceptor component (binary and ternary active layers),
- modification of hole transporting layer by use of new polymers instead of PEDOT:PSS,
- modification of device architectures (inverted, tandem devices),
- modification of device substrate (stiff, flexible solar cells),
- modification of method of encapsulation of devices towards enhancing the stability of devices,
- modification of cathode and anode in devices
- modification of methods of layerformation in devices
- the use of hybrid configurations that integrate semiconducting polymers as well as nanomaterials such as graphene or inorganic nanoparticles.
- the interfacial chemistry that allow the integration of such materials to the polymeric phase. i.e. surface functionalization
- charge transfer mechanisms in hybrid devices
- novel architectures/materials in QDSSCs and DSSCs
The aim of this symposium is to bring together chemists, physicists, engineers, and technologists to discuss new aspects in organic solar cells towards their practical applications. The scope includes polymer and organic solar cells, dye sensitized solar cells (DSSC) and perovskite devices. Papers are also being solicited in the area of nanoparticles as they relate to photovoltaics.
Papers relating to all aspects of the following six themes are invited:
- Organic solar cells with graphene and carbon nanotubes
- Perovskite solar cells
- Nanoparticles in organic solar cells
- Dye and quantum dot sensitized solar cells
- Encapsulation of organic solar cells
- Large area organic solar cells
Hot topics to be covered by the symposium:
- Organic solar cells with graphene and carbon nanotubes
- Perovskite solar cells
- Nanoparticles in organic solar cells
- Dye and quantum dot sensitized solar cells
- Encapsulation of organic solar cells
- Large area organic solar cells
- Andreas Hinsch, Fraunhofer Institute for Solar Energy Systems ISE, Freiburg, Germany
List of invited speakers:
- Silvija Gradecak, Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, United States
- Ning Li, Institute of Materials for Electronics and Energy Technology (i-MEET), Friedrich-Alexander- University Erlangen-Nuremberg, Martensstraße 7, 91058 Erlangen, Germany
- Mohammad Khaja Nazeeruddin, Group for Molecular Engineering of Functional Materials, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, Sion, Switzerland
- Tom Savenije, Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology, Delft, Netherlands
- Ravi Silva, Nano-Electronics Centre, Advanced Technology Institute, University of Surrey, Guildford, United Kingdom
- Jizheng Wang, Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Chinese Academy of Sciences, Beijing, China
- Chuanlang Zhan, Beijing National Laboratory of Molecular Science, Key Laboratory of Photochemistry, Chinese Academy of Sciences, Beijing, China, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China
- Mohite Aditya, Materials Synthesis and Integrated Devices, Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, NM, United States
- John Grey, Department of Chemistry and Chemical Biology, MSC03 2060, University of New Mexico, Albuquerque, NM, United States
- Aldo Di Carlo, C.H.O.S.E. (Centre for Hybrid and Organic Solar Energy), Department of Electronic Engineering, University of Rome Tor Vergata, via del Politecnico 1, Rome, Italy
- Itaru Osaka, RIKEN Center for Emergent Matter Science (CEMS), 2-1 Hirosawa, Wako, Saitama, Japan
- Masayuki Chikamatsu, Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan
- Uli Würfel, Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstrasse 2, Freiburg, Germany
- Feng Yan, Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China
- Denis Andrienko, Max Planck Institute for Polymer Research, Mainz, Germany
- Konrad Wojciechowski, Saule Technologies, Wroclaw, Poland
- Filippo De Angelis, Computational Laboratory for Hybrid/Organic Photovoltaics (CLHYO), CNR-ISTM, Perugia, Italy
- Joel Jean, Organic and Nanostructured Electronics Lab, Massachusetts Institute of Technology
- Johan Bijleveld, Technische Universiteit Eindhoven, Molecular Materials and Nanosystems, Eindhoven, Netherlands
- Bernardo A. Frontana-Uribe, Laboratorio de electroquímica y electrosíntesis, Centro Conjunto de Investigación en Química Sustentable UAEMéx-UNAM, Toluca, Estado de México, México
- Christoph J. Brabec, University of Erlangen-Nürnberg, DE
- Theo Dingemans, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg, The Netherlands
- Marek Godlewski, Institute of Physics, Polish Academy of Sciences, Warsaw, Poland
- Maria Kaminska, Faculty of Physics,University of Warsaw, Poland
- Malgorzata Lewandowska, Faculty of Materials Science and Engineering, Warsaw University of Technology, Poland
- Jean-Michel Nunzi, Queen’s University, Ontario, Canada
- Niyazi Serdar Sariciftci, Linz Institute for Organic Solar Cells, Austria
- Tomasz Szoplik, Faculty of Physics,University of Warsaw, Poland
- Marek Tłaczała, Faculty of Microsystem Electronics and Photonics, Wrocław University of Technology, Poland
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Perovskites solar cells I : Agnieszka IWAN
Authors : Andreas Hinsch
Affiliations : Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstraße 2, 79110 Freiburg, Germany, firstname.lastname@example.org
Resume : Perovskite solar cells (PSC) are still mostly at the stage of university research. After a certified laboratory efficiency value over 20 % was attained in 2015 for solution deposited perovskite solar cells, a strong research interest has been triggered world-wide. In particular the double nature of the electronic and ionic behavior in perovskite solar cells has to be understood better. Parallel to fundamental research, it is now necessary to develop suitable concepts for up-scaling the cells in a cost-effective process. Over the past years, large-area stable dye solar modules on glass substrates have been successfully developed at Fraunhofer ISE . The solar cells are fabricated from solutions within a module that is first hermetically sealed by low-melting glass solder. As the recent work demonstrates, this technology can be transferred very well to the field of perovskite solar cells. The perovskite is recrystallized in-situ in the porous electrode structure. The procedure enables future perovskite solar modules to be produced with minimal consumption of resources and at very low costs. In this presentation, material, characterization and stability related questions arising from the in-situ concept will be discussed and latest results from on-going work on test cell and module level will be reported.  A. Hinsch et al.,: Status of Dye Solar Cell Technology as a Guideline for Further Research. In: ChemPhysChem 15 (6), S. 1076–1087. (2014) DOI: 10.1002/cphc.201301083.
Authors : Edoardo Mosconi, Daniele Meggiolaro, Filippo De Angelis
Affiliations : Computational Laboratory for Hybrid/Organic Photovoltaics (CLHYO), CNR-ISTM, I-06123, Perugia, Italy; CompuNet, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy.
Resume : Organohalide lead-perovskites have revolutionized the hybrid/organic photovoltaics landscape. Despite the fast efficiency increase, some of the materials properties related to their extraordinary photovoltaic performance remain largely not understood. Further advances in the perovskite solar cells (PSCs) field may be boosted by computational design and screening of new materials, with researchers examining material characteristics that can improve device performance and/or stability. Suitable modeling strategies may allow researchers to observe the otherwise inaccessible but crucial hetero-interfaces that control the operation of PSCs, allowing researchers the opportunity to develop new and more efficient materials and to further optimize the solar cells photophysics. We illustrate the results of ab initio molecular dynamics simulations coupled to first principles electronic structure calculations on the interplay of nuclear dynamics and electronic properties in the prototypical MAPbI3 and related perovskites. The role of the organic cation dynamics and of ion/defect migration is analyzed in relation to photoinduced structural transformations and solar cell operation. We also show how the fluctuations of the organic cations may locally (in space and time) impart the otherwise centrosymmetric perovskite lattice with spin-orbit coupling dependent properties which are typical of ferroelectric crystals characterized by lack of inversion symmetry. A possible polaronic mechanism, triggered by a photoinduced structural deformation, is finally presented which may be responsible for the reduced electron/hole recombination observed in organohalide perovskites. References: • F. De Angelis Acc. Chem. Res 2014, 47, 3349. • F. De Angelis et al. Chem. Rev. 2014, 114, 9708. • A. Amat et al. Nano Lett. 2014, 14, 3608. • P. Umari et al. Sci. Rep. 2014, 4, 4467. • V. Roiati et al. Nano Lett. 2014, 14, 2168. • E. Mosconi et al. J. Phys. Chem. Lett. 2014, 5, 2619. • J.M. Azpiroz et al. Energy Env. Sci. 2015, 8, 2118. • C. Quarti et al. Energy Env. Sci. 2016, 9, 155.
Authors : Antonio Abate
Affiliations : University of Fribourg, Adolphe Merkle Institute Chemin des Verdiers 4, CH-1700, Fribourg, Switzerland
Resume : Perovskite solar cells are currently one of the most promising photovoltaic technologies for highly efficient and cost-effective energy production. In only several years, an unprecedented progression of preparation procedures and material compositions delivered a prototype technology that exploits most of the potential for perovskites as photovoltaic materials. However, there still remains a huge scope to demonstrate that perovskite solar cells are stable under working conditions. Migration of ions and associated trap states within the perovskite crystal lattice have been widely investigated to explain the “hysteresis” of current-voltage (J-V) characteristic of perovskite solar cells. The results of these studies indicated that, regardless of the particular device architecture and materials composition, ion (and ion vacancies) migrate within the perovskite layer and accumulate at the interface with charge selective contacts. Depending on particular voltage and light bias conditioning, accumulation of ions and associated trap states may induce a charge extraction barrier and recombination losses. This mechanism has been suggested as the most likely cause of J-V “hysteresis”, but it may also have a significant impact on the long-term stability of devices under working conditions. Understanding the impact of ion migration on device long-term performance is of paramount importance because it will answer the question whether or not there is an intrinsic instability that may ultimately prevent using perovskites for photovoltaics. In this talk, I will demonstrate ion migration in perovskite solar cells working under different voltage bias conditions and I will discuss the impact of ion migration on the initial device power conversion efficiency and long-term stability.
Perovskites solar cells II : Jean-Michel NUNZI
Authors : Masayuki Chikamatsu
Affiliations : Research Center for Photovoltaics (RCPV), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, JAPAN
Resume : Stability is one of the important issue for application of organic solar cells. For realization of higher stability, we should analyze the degradation mechanism and improve organic semiconductor materials, device structures and encapsulation techniques. In this work, we performed photo-oxidation studies on DTS(FBTTh2)2:fullerene bulk-heterojunction (BHJ) films, one of the promising small-molecule materials for organic solar cells. The results of two-dimensional grazing-incidence wide-angle X-ray scattering and absorption spectroscopic analyses indicate that increasing the crystallinity of DTS(FBTTh2)2: fullerene BHJ films improved their photostability . In addition, for the development of encapsulation of flexible devices, we examined the influence of temperature and humidity on the stability of polymer solar cells encapsulated using various dam and fill materials. Optimized flexible solar cells showed high stabilities (650 hours at 85ºC, 85%RH and 1700 hours at 60 ºC, 90%RH). We have also investigated perovskite solar cells focusing on fundamental studies such as in-situ x-ray measurement of perovskite thin-film growth by solution process  and ellipsometry analysis of the perovskite film by laser deposition process [3,4].  S. Yamane et al. Sol. Energy Mater. Sol. Cells., 151, 96-101 (2016).  T. Miyadera et al., Nano Lett., 15, 5630-5634 (2015).  M. Shirayama, et al, Phys. Rev. Appl., 5, 014012 (2016).  M. Shirayama, et al, J. Appl. Phys., 119, 115501 (2016).
Authors : Konrad Wojciechowski
Affiliations : Saule Technologies Ltd, Wroclaw, Poland
Resume : Metal halide perovskites constitute a very attractive class of materials for optoelectronic applications, such as solar cells, light emitting diodes, lasers and photodetectors.1 Most notably, solid-state photovoltaic devices based on these materials have reached power conversion efficiencies (PCEs) of 22% after just five years of academic research.2 Perovskite solar cells have a great commercial potential, but there still remain few challenges, which need to be resolved to prove the viability of the technology. Some of the well-known issues include material stability and presence of lead in the active layer. Furthermore, cost-effective, reliable fabrication process capable of delivering highly efficient, large-area perovskite modules is yet to be demonstrated. Here, we present a fully scalable ink-jet printing process of the entire perovskite PV stack, carried out in ambient atmosphere, with PCEs exceeding 10% for the active areas larger than 1cm2. Furthermore, we present cost evaluation of the technology which has potential to disrupt the market of flexible photovoltaics, with a number of future applications being discussed. Finally, we present a regulatory status of Pb-based perovskites, and show different avenues for providing durable and robust product based on these materials. References: 1. Stranks, S. D. & Snaith, H. J. Metal-halide perovskites for photovoltaic and light-emitting devices. Nat. Nanotechnol. 10, 391?402 (2015). 2. NREL. http://www.nrel.gov/ncpv/images/efficiency_chart.jpg. http://www.nrel.gov/ncpv/images/efficiency_chart.jpg
Authors : Hamed Abdy, Arash Aletayyeb, Mohammadreza Kolahdouz, Ebrahim Asl-Soleimani, Ala Mohajerzade, Zahra Heydari
Affiliations : ECE Department, School of Electrical and Computer Engineering, University of Tehran, Tehran, Iran; ECE Department, School of Electrical and Computer Engineering, University of Tehran, Tehran, Iran; ECE Department, School of Electrical and Computer Engineering, University of Tehran, Tehran, Iran; ECE Department, School of Electrical and Computer Engineering, University of Tehran, Tehran, Iran; ECE Department, School of Electrical and Computer Engineering, University of Tehran, Tehran, Iran; ECE Department, School of Electrical and Computer Engineering, University of Tehran, Tehran, Iran
Resume : Recently metal trihalide perovskite materials have excited photovoltaic research and industrial community due to their potential optoelectronic applications. Several different methods have been introduced for the synthesis of perovskite materials so far. The synthesis method highly affects the morphology of the perovskite layer. Another important factor in final morphology is clearly the effect of the substrate. In this work, two-step and solvent engineering synthesis methods are compared in terms of morphology and crystallinity in ambient air condition. Different substrate morphologies using TiO2 nanoparticles have also been used for investigating the effect of substrate on final morphology. In both methods, solutions are spin-coated on TiO2 nanoparticles for obtaining the perovskite (CH3NH3PbX3, X = Br, I) layer. Since perovskite materials are so sensitive to oxygen and steam, one might expect weak layer morphology and crystallinity in ambient air condition. In this study, this assumption was shown to be correct for solvent engineering method, but in two step spin coating, despite of negative effect of ambient air condition, we have succeeded to reach uniform morphology and good crystallinity without using glovebox. Different techniques have used for characterization of synthesized perovskite layers. An image processing tool has also developed and used on scanning electron microscope (SEM) pictures for measuring the amount of perovskite layer coverage in different samples.
Authors : Azat F. Akbulatov,1 Lyubov A. Frolova,1 Serdey Luchkin,2 Keith J. Stevenson,2 and Pavel A. Troshin 2,1
Affiliations : 1 Institute for Problems of Chemical Physics of RAS, Semenov ave. 1, Chernogolovka, Moscow region, 142432, Russia. 2 Skolkovo Institute of Science and Technology, Skolkovo Innovation Center, Nobel st. 3, Moscow, 143026, Russian Federation
Resume : Hybrid lead iodide based perovskites (e.g. CH3NH3PbI3) have recently demonstrated outstanding electronic properties such as low exciton binding energy (~2 meV), high electron-hole diffusion lengths (>150 m) and excellent charge carrier mobility (>100 cm2V 1s 1). Thin-film perovskite solar cells have delivered certified efficiencies >20%, though industrial application of this technology is hindered by stability issues. While much research has been done to prevent moisture-induced decomposition of hybrid perovskites, studies on degradation pathways that influence their intrinsic stability is lacking. Here we will discuss thermal, photochemical and electrochemical degradation pathways of a series of complex iodoplumbates APbX3 (A+ = CH3NH3+, [HC(NH2)2]+, Cs+; X=I, Br, I/Cl, I/Br) in the absence of exposure to oxygen and moisture (glove box environment). We will show that the most common materials (e.g. MAPbI3) undergo strong thermal degradation at the temperatures >60 oC. Light-induced degradation occurs rapidly at 40-50 oC and cannot be completely prevented even at the temperatures as low as 10-20 oC. Significant field-induced changes in the perovskite films occur at the potentials about1 V for 250-350 nm thick films. These results strongly suggest that the current generation of perovskite absorbers are not amenable for practical applications. There is an urgent need for novel materials that can deliver sufficient performance with high stability required for industrial-scale application of the perovskite PV technology.
Perovskites solar cells III : Takeshi FUKUDA
Authors : Aldo Di Carlo, Antonio Agresti, Sara Pescetelli
Affiliations : CHOSE (Centre for Hybrid and Organic Solar Energy), Department of Electronics Engineering, University of Rome "Tor Vergata".
Resume : In the broad context of graphene applications , new generation photovoltaic underwent beneficial effects in terms of efficiency, stability and costs by inserting graphene based materials in the devices structure . In particular, the dramatic development exhibited in the last few years by perovskite solar cells (PSC) technology has triggered the scientific community efforts in findings more efficient and stable PSC structures  by employing Graphene and other 2D materials (GRM). Lithium-neutralized graphene oxide (GO-Li) has been shown to act as an efficiency electron transporting layer (ETL) , while Reduced Graphene Oxide  or functionalized Graphene Oxide in P3HT  can act as Hole Transporting Layer (HTL) improving the stability of the cell. Moreover, GRM can be efficiently used for large area Perovskite modules improving at the same time efficiency and stability. In this communication, we will report on the efforts made to scale up perovskite solar cells to modules with sizes larger than 100 cm2 and efficiency exceeding 12% exploiting the use of GRM. References  A. C. Ferrari et al., Nanoscale, 7, 4587, (2015)  E. Singh, H. Singh Nalwa, Journal of Nanoscience and Nanotechnology, 15, 6237, (2015)  N.-G. Park, Materials Today, 18, 65, (2015)  A. Agresti et al., Advanced Functional Materials, 26, 2686 (2016)  A. L. Palma et al . Nano Energy(2016) 22, 349–360  S. Casaluci et al. Proc. IEEE NANO 2015, 27th-30th July 2015, Rome (Italy)
Authors : S. Ravi P. Silva, José V. Anguita, Muhammad Ahmad, Jeremy Allam and Sajad Haq
Affiliations : S. Ravi P. Silva, José V. Anguita, Muhammad Ahmad, Jeremy Allam: Advanced Technology Institute (ATI), University of Surrey, Guildford, Surrey, GU2 7XH, United Kingdom; Sajad Haq: QinetiQ, Cody Technology Park, Ively Road, Farnborough, GU14 0LX, United Kingdom.
Resume : The development of techniques to couple light into novel forms of carbon, such as graphene, is crucial to allow the exploitation of the potential optoelectronic properties of these materials. Much research in this field is a result of highly absorbing carbon nanostructures such as tall forests of multiwalled carbon nanotubes (order of mm). These have been noted as the worlds’ darkest materials, such as Vantablack. However, despite the excellent optical absorption properties, it is difficult to incorporate this material into nanometer-sized devices. Graphene, the thinnest carbon allotrope known, exhibits unique electrical characteristics that arise from its linear dispersion and semimetal behavior. These offer new opportunities from a fundamental perspective, and thus have projected new light onto the roadmap of a diverse range of electronic applications. To unlock this potential, it is necessary to develop the technologies needed to produce this material properly over technologically relevant substrates. It is believed that graphene-based devices will form the basis for the era of the “internet of things”. Currently, graphene-based devices remain mostly blind to light, as it only absorbs ~ 2.3% of the light that is incident on it. Here, we have learned from nature (the eye of the moth) to develop technologies for enhancing the absorption of light. For millennia, moths have developed unique abilities for light-absorption that enable them to see in the dark. We reproduce the nanostructures that moths have developed over metallic substrates, and use the metal particles to nanotexture a few-layer de-coupled graphene. Our results show a strong enhancement in the ability of the graphene layers to absorb the light, over an ultra-broadband range, spanning from the mid-IR to the UV. We show, using finite-element computer analysis, how the nanostructures are able to channel and enhance the optical field into the regions where the graphene absorber is located. In our work we present the experimental realization and functioning of this nanometer-sized ultra-broadband graphene absorber, and demonstrate its applicability in the production of a blackbody absorber on top of an opto-electromechanical device.
Authors : Irene Grill, Michiel Petrus, Nadja Giesbrecht, Thomas Bein, Pablo Docampo, Matthias Handloser, Achim Hartschuh
Affiliations : Irene Grill 1,2; Michiel Petrus 1,2; Nadja Giesbrecht 1,2; Thomas Bein 1,2; Pablo Docampo 1,2; Matthias Handloser 1,2; Achim Hartschuh 1,2 1 Department of Chemistry and Center for NanoScience (CeNS), Ludwig-Maximilians-Universität München, Butenandtstr. 11, 81377 Munich, Germany 2 Nanosystems Initiative Munich (NIM), Ludwig-Maximilians-Universität München, Schellingstr. 4, 80799 Munich, Germany
Resume : Organic-inorganic hybrid perovskites currently represent one of the most promising photoactive material systems for incorporation in future solar cell devices since their power conversion efficiencies increased enormously in the last few years, pointing values which are competitive with the nowadays used commercial technologies. In addition, their fabrication is easily realized via solution processing by employing cheap and earth-abundant bulk materials and thus makes them potential candidates for photovoltaic applications with currently achieved efficiencies (PCE) exceeding 21%. [1,2] To date, a huge effort of scientists from different fields is spent on the understanding of the fundamental optoelectronic properties including charge carrier dynamics in metal-halide perovskites and the respective interlayer transport in the stacked device architecture of perovskite based thin film solar cells. The knowledge of these material properties is crucial for well performing devices and their further improvement. In this work, we determine the transport time of photoinduced charges in between the top- and bottom-electrode upon pulsed laser excitation in different metal-halide perovskite thin film solar cell devices, based on Time-of-Flight (ToF) transient photocurrent measurements. The ToF results are discussed in terms of the respective device efficiencies, optical properties and film morphologies. To extract the influence of the individual layers on the charge transport characteristics and to identify limiting factors (i.e interface effects, low mobility sheets), we carried out additional ToF studies on the respective layers of the photovoltaic device in a lateral device architecture. The direct comparison of the ToF-data obtained for the individual layers with the results of the working device allows for the optimization of fabrication techniques and device architecture to enhance light to energy conversion in novel perovskite based solar cells. References  M.A. Green and T. Bein, Nature Mater. (2015), 14, 559-561.  M. Saliba et al., Energy Environ. Sci. 2016, DOI: 10.1039/C5EE03874J.
Perovskites solar cells IV : Michiel PETRUS
Authors : Mohammad Khaja Nazeeruddin
Affiliations : Group for Molecular Engineering of Functional Materials, Institute of Chemical Sciences and Engineering, Ecole polytechnique fédérale de Lausanne, CH-1951 Sion, Switzerland
Resume : Organo-metal trihalide perovskites have revolutionized the field of thin film solar cells due to their meteoric rise of power conversion efficiency (PCE) of a record value 22%.1 The high efficiency is due to strong light absorption from the visible into the near-infrared spectral region, long carrier diffusion length, and tailorable optoelectronic properties through compositional engineering of halides and cations. These properties are subservient to the formation and nature of the crystals, morphology, and growth. One of the most fantastic features of organo-metal trihalide perovskite is its ability to self-assemble between precursors of vapour-vapour, solution, solid-solution phases into high quality crystalline thin films at ambient conditions. Despite the high efficiency and excellent opt-electronic properties the biggest problem of organo-metal trihalide perovskite is stability under heat and light soaking conditions. In this talk we present various deposition methods for perovskite absorbing layer, synthesis and characterization of novel hole transporting materials to address the stability and hysteresis issues.2,3 (1). Burschka, J., Pellet, N., Moon, S-J., Humphry-Baker, R., Gao, P., Nazeeruddin. &Grätzel, M, Nature 499, 316−319 (2013). (2). www.nrel.gov/ncpv/images/efficiency_chart.jpg. (3). A molecularly engineered hole-transporting material for efficient perovskite solar cells, Michael Saliba & Mohammad Khaja Nazeeruddin, Nature Energy 1, Article number: 15017 (2016), doi:10.1038/nenergy.2015.17
Authors : M. Kot1,*, C. Das1, K. Wojciechowski2, Z. Rouissi1, H. J. Snaith2 and D. Schmeißer1
Affiliations : 1BTU Cottbus?Senftenberg, Konrad-Wachsmann-Allee 17, 03046 Cottbus, Germany 2Clarendon Laboratory, University of Oxford, Parks Road, Oxford, OX13PU, UK *Corresponding author e-mail address: email@example.com.
Resume : Hybrid perovskites represent a new paradigm for photovoltaics, which have the potential to overcome the performance limits of current technologies and achieve low cost and high versatility. However, for the successful commercialization not only highly efficient but also long-term stable perovskite solar cells are needed. In this work, we study the Al2O3 growth by atomic layer deposition (ALD) on CH3NH3PbI3 perovskite at room temperature in order to prevent perovskite film from the thermal degradation which is known to take place already at 85°C. High energy resolution synchrotron-based X-ray photoelectron spectroscopy and atomic force microscopy studies indicate that room temperature ALD Al2O3 film grows on the perovskite surface, first in a layer by layer form, and then forming 3D islands. The stability test of the perovskite film upon air exposure has shown that an ultrathin alumina layer significantly enhances its lifetime. This finding opens new possibilities to increase the stability of the perovskite solar cells where the low temperature processing is mandatory to protect the perovskite film against degradation.
Authors : M.Kot1,*, C. Das1, K. Wojciechowski2, H. J. Snaith2 and D. Schmeißer1
Affiliations : 1BTU Cottbus?Senftenberg, Konrad-Wachsmann-Allee 17, 03046 Cottbus, Germany 2Clarendon Laboratory, University of Oxford, Parks Road, Oxford, OX13PU, UK *Corresponding author e-mail address: firstname.lastname@example.org
Resume : Solar cells based on hybrid organic?inorganic perovskites are currently one of the fastest improving new emerging photovoltaic technologies. The understanding of the fundamental electronic and optical properties of CH3NH3PbI3 and related metal halide perovskites represents a key step in the future development of hybrid perovskite optoelectronic devices. To date, there are only few reports, mostly based on theoretical calculations, describing the electronic structure of CH3NH3PbI3 perovskite based solar cells. DFT calculations revealed that the valence band maximum and the conduction band minimum are predominantly of I5p and Pb6p character, respectively. The electronic states associated with the CH3NH3 cation are located more than 5 eV away from the band edges, therefore they are not directly involved in the optical absorption . However, our synchrotron-based resonant photoelectron spectroscopy (resPES) study of the CH3NH3PbI3 perovskite films at the nitrogen K absorption edge revealed that there is a significant contribution of nitrogen to the electronic structure. In particular, we observe distinct resonances with separate energies which can be attributed to a strong interaction of nitrogen with lead and iodine as well as a weak but noticeable contribution of nitrogen to the valence band. A detailed nitrogen K-edge resPES data analysis will be presented.  Marina R. Filip and Feliciano Giustino, Physical Review B 90, 245145 (2014).
Poster Session : Ravi SILVA
Authors : Claire Verrier 1.2, Romain Parize 1, Estelle Appert 1, Quentin Rafhay 2, Vincent Consonni 1, and Anne Kaminski-Cachopo 2.
Affiliations : 1. Université Grenoble Alpes, CNRS, LMGP, F-38000 Grenoble, France 2. Université Grenoble Alpes, CNRS, IMEP-LAHC, Minatec, Grenoble INP, F-38000 Grenoble, France
Resume : The development of ZnO nanowire (NW)-based dye-sensitized solar cells (DSSCs) has received increasing interest over the last years ZnO is a good candidate for the DSSCs owing to its much higher mobility than TiO2 and its ability to form nanostructures with different shapes using low cost deposition techniques. The association of ZnO NWs with ZnO nanoparticles (NPs) constitutes a nanocomposite which has already demonstrated better efficiencies in DSSCs than NWs or NPs alone : NWs confer high electron diffusion while NPs allow high dye absorption (due to an increased specific surface area). Also, the fabrication of ZnO / TiO2 core shell NW array-based DSSCs has also been efficiently achieved to improve the interface properties with dye . In that work, the combination of ZnO nanocomposites with a TiO2 shell in DSSCs is thoroughly investigated. Both ZnO NWs and NPs are grown by chemical bath deposition while the TiO2 shell is deposited by atomic layer deposition. Their structural morphologies are studied by scanning and transmission electron microscopy while their photovoltaic performances are revealed by I(V), absorption, and external quantum efficiency measurements. A special emphasis is made on the doping of ZnO NWs and its effects on the performances of the resulting DSSCs.  E. Puyoo, G. Rey, E. Appert, V. Consonni, and D. Bellet, J. Phys. Chem. C 116, 18117 (2012)  C. Xu, J. Wu, U. V. Desai and D. Gao, JACS 133, 8122 (2011)
Authors : Qana A. Alsulami, Banavoth Murali, Yara Alsinan, Manas R. Parida, Shawkat M. Aly, and Omar F. Mohammed
Affiliations : Solar and Photovoltaics Engineering Research Center King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
Resume : Remarkably High Conversion Efficiency of Inverted Bulk Heterojunction Solar Cells: From Ultrafast Laser Spectroscopy and Electron Microscopy to Device Fabrication and Optimization -------------------------------------------------------------------------------------------------------------- In organic donor–acceptor systems, ultrafast interfacial charge transfer (CT), charge separation (CS), and charge recombination (CR) are key determinants of the overall performance of photovoltaic devices. However, a profound understanding of these photophysical processes at device interfaces remains superficial, creating a major bottleneck that circumvents advancements and the optimization of these solar cells. Here, results from time-resolved laser spectroscopy and high-resolution electron microscopy are examined to provide the fundamental information necessary to fabricate and optimize organic solar cell devices. In real time, CT and CS are monitored at the interface between three fullerene acceptors (FAs) (PC71BM, PC61BM, and IC60BA) and the PTB7-Th donor polymer. Femtosecond transient absorption (fs-TA) data demonstrates that photoinduced electron transfer from the PTB7-Th polymer to each FA occurs on the sub-picosecond time scale, leading to the formation of long-lived radical ions. It is also found that the power conversion efficiency improves from 2% in IC60BA-based solar cells to >9% in PC71BMbased devices, in support of our time-resolved results. The insights reported in this manuscript provide a clear understanding of the key variables involved at the device interface, paving the way for the exploitation of efficient CS and subsequently improving the photoconversion efficiency.
Authors : Kurt Taretto, Marcos Soldera
Affiliations : PROBIEN, Dto. de Electrotecnia, CONICET, Univ. Nacional del Comahue
Resume : Current perovskite solar cells reach high efficiencies with inexpensive materials and preparation methods. In order to understand and surpass the efficiency beyond current values, the fundamental loss mechanisms of perovskite solar cells must be understood and predicted by appropriate models. Here, we adapt an analytical, drift-diffusion model for p-i-n solar cells and fit measured current voltage characteritics of planar hysteresis-free perovskite solar cells covering a range of perovskite thickness. Our results give values of carrier recombination liftimes higher than 4 µs, low effective recombination velocities at the interfaces between the perovskite layer and the surrounding layers, which are under 100 cm/s, and built-in voltages that are slightly lower than the difference of work functions of the contacting layers. Moreover, the fits yield carrier mobilities around 0.05 cm^2/Vs, considerably lower than values obtained in perovskite single crystals. These first results are discussed and compared with literature values obtained by direct measurements performed on perovskite films.
Authors : Michal Wrzecionek (1), Daniel Jastrzebski (1), Piotr Ostapowicz (1), Grzegorz Matyszczak (1), Karolina Pietak (1), Dorota Brzuska-Kamoda (1), Slawomir Podsiadlo (1)
Affiliations : (1) Faculty of Chemistry, Warsaw University of Technology; Noakowskiego 3, 00-664 Warsaw, Poland
Resume : Kesterite (CZTS) is hopeful material for solar cells. It is cheaper and more less toxic than CIGS, CdSe or CdTe. This study has focused on synthesis and characterization of nano kesterite powders. The syntheses have been carried out in organic solvents, using simply substrates. Molecular printing ink is a new method, which can be used in solar cells fabrication. The obtained materials have been characterized with X-ray powder diffraction, transmission electron microscopy and atomic force microscopy.
Authors : Bartosz Boharewicz, Agnieszka Hreniak, Agnieszka Iwan
Affiliations : Electrotechnical Institute, Division of Electrotechnology and Materials Science, M. Sklodowskiej-Curie 55/61 Street, 50-369 Wroclaw, Poland
Resume : In this paper we are presented influence of cathode buffer layer (CBL) on efficiency of organic solar cells based on PTB7:PC71BM active layer. Modified devices were treated by various alcohols such as methanol, ethanol, isopropanol, butanol, pentanol, hexanol and 2-methoxyethanol. First investigations show increase of short-circuit current (Jsc) from 16.3 mA/cm2 to 18 mA/cm2 for 2-methoxyethanol applied such a cathode buffer layer. One theory described CBL talks about dipole moments of solvents which were used on the active layer . Authors attributed them a big role to alignment the energy level between blend/CBL and/or CBL/cathode interface. From these researched solvents the biggest dipole moment had a 2-methoxyethanol, which showed the best photovoltaic performances with PTB7:PC71BM blend in device. Alcohol treatments influence also on the morphology of the created active layer. Probably this effect appearance on other combinations polymer:fullerene. From the other hand, increase of Jsc, FF and Voc was attributed to change in hole mobilities and more balanced charge transport . This promising method can be used as a cheap way to increase photovoltaic properties of polymer solar cells.  B. Qi, Z.-G. Zhang, J. Wang, Uncovering the role of cathode buffer layer in organic solar cells. Sci. Rep. 5, 7803; 2015.  Y. Wang, Y. Lu, S. Chen, R. Peng, Z. Ge. Significant Enhancement of Polymer Solar Cell Performance via Side-Chain Engineering and Simple Solvent Treatment. Chem. Mater. 25, 3196, 2013.
Authors : Tomasz Lecki, Magdalena Skompska, Kamila Zarembska
Affiliations : Laboratory of Electrochemistry, Faculty of Chemistry, Warsaw University
Resume : The purpose of this work was to obtain the solar cell based on Perovskite, and to study the influence of the methods of preparation of the cell on its performance. The prepared solar cells have following scheme: FTO/TiO2 (or ZnO)/ Perovskite(CH3NH3PbI3) /CuSCN (or P3HT)/Au FTO/TiO2 (or ZnO)/Perovskite(CH3NH3PbI3)/CuSCN (or P3HT) /Pt/ FTO The aim of the work was: - to prepare a thin and uniform layer of the electron transporting material (ETM) on FTO substrate; - to achieve good integrity of ETM and hole transporting material (HTM) with perovskite photoactive layer and improve mobility of the charge carriers through ETM and HTM; - to optimize the process of preparation of Perovskite and enhance its sustainability by protecting against degradation; - to explain the effect of each layer on the working parameters of the solar cell. The components of the cells were prepared with the use of chemical and electrochemical methods. Optical and structural properties were studied by UV-VIS and Raman spectroscopy, while morphology of the subsequent layers was examined by optical and scanning electron microscopies. The working parameters of the cells were extracted from I-V measurements under illumination with solar simulator.
Authors : Chiu-Yee Chan a, Yu-Fang Wei a, Hrisheekesh Thachoth Chandran a, Chun-Sing Lee a, b , Ming-Fai Lo a, b* and Tsz-Wai Ng a, b *
Affiliations : Center of Super-Diamond and Advanced Films (COSDAF), Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR, P. R. China.
Resume : We reported an efficient bulk-heterojunction solar cell of Boron subphthalocyanine chloride- Fullerene with Ultra-violet (UV) ozone treated zinc oxide (ZnO) buffer layer at anode. By modifying the root mean square roughness of ZnO and UV ozone treated, the power conversion efficiency increases from 2.55% to 3.2 % under under AM1.5G illumination (100mWcm-2) as well as short circuit density and open circuit voltage. The improvement in absorbance increases the short-circuit density from 5.0 to 5.9 mA/cm2 and the high work function after UV ozone treatment which reduce the leakage current increases the Voc of solar cell from 0.9V to 1.06V. We also demonstrated that the device has a better stability since the reduction of work function under 1 day high vacuum storage.
Authors : Angelika Maderitsch, Sebastian Wilken, Christof Pflumm, Herwig Buchholz, Holger Borchert, Jürgen Parisi
Affiliations : Energy and Semiconductor Research Laboratory, Department of Physics, Carl von Ossietzky University of Oldenburg; Energy and Semiconductor Research Laboratory, Department of Physics, Carl von Ossietzky University of Oldenburg; Merck KGaA; Merck KGaA; Energy and Semiconductor Research Laboratory, Department of Physics, Carl von Ossietzky University of Oldenburg; Energy and Semiconductor Research Laboratory, Department of Physics, Carl von Ossietzky University of Oldenburg
Resume : Efficient organic light-emitting diodes (OLEDs) are multilayer devices that contain a hole transport layer, an emitting layer and an electron transport layer between two electrodes, one transparent as ITO. The morphology of these layers is important for device performance. A well-established fabrication method is vapor deposition under vacuum condition. Other methods are solution processing by spin coating or ink-jet printing. Especially ink-jet printing promises an easy and cost efficient manufacturing process of OLEDs in large scales. However, differences in efficiency and life time can be observed. To get a deeper insight into the influence of the preparation method on the morphology of the layer structure, samples with an emitter layer prepared by vacuum deposition, were compared to those with solution processed layers made of the same emitter. To get direct access to the layered structure TEM-lamellas were prepared using FIB-milling. An electron transparent TEM-lamella should have a thickness of less than 100nm. Such samples may lead to a very low count rate in EDX-spectra. A special preparation method has been developed to overcome this issue. With TEM-EDX analysis, the element distribution through the layer stack was determined. The differences observed between the preparation methods are discussed. These methods can also be applied to organic solar cells.
Authors : K. P. Korona1, W. Mech1, S. Grankowska1, M. Kamińska1, M. Sobanska2, G. Tchutchulashvili2, K. Klosek2, Z. R. Zytkiewicz2, A. Iwan3
Affiliations : 1 Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland; 2 Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46, 02-668 Warsaw, Poland; 3 Division of Electrotechnology and Materials Science, Electrotechnical Institute, ul. M. Skłodowskiej-Curie 55/61, 00-369 Wroclaw, Poland;
Resume : In recent years it has been found that GaN/Si nanowires (NWs) are promising building blocks for new optoelectronic devices. Due to easy accommodation of lattice mismatch, the NWs can be easily grown even on multicrystalline silicon used for solar cells. In this work we report optical and electro-optical studies of GaN nanowires, pure and covered with polymers: poly(3-hexylthiophene) (P3HT) or polyazomethine (2252Th-DMB) that turned out to be very promising and stable material. GaN nanowires were grown catalyst-free by plasma-assisted molecular beam epitaxy on in-situ nitridized Si(111) substrates. They had diameters of about 50 nm and length of about 1 µm. Time-resolved photoluminescence measurements of the nanowire structures were performed using a streak camera. They showed that the exciton peaks have long lifetimes and are exactly in the same position as in unstrained GaN. Reflection measurement revealed clear interference fringes what proved that the ensemble of NWs works as an effective optical layer. For energy above 2.5 eV an increase of absorption was observed that could be due to photonic effects inside the NWs ensemble. Photocurrent spectroscopy of solar cells made of GaN/Si NW covered with P3HT or 2252Th-DMB revealed that photocurrent was generated by all active layers, what meant that the structure was a broad band absorption cell. There was clear input from silicon starting at 1.1 eV, from polymers starting at about 2 eV as well as from GaN starting at 3.5 eV.
Authors : M. Morawski (1), K. Startek (1), M. Łysień (1), M. Dusza (1,2), F. Granek (1)
Affiliations : (1) Wrocław Research Centre EIT+, Stabłowicka 147, 54-066 Wrocław, Poland; (2) Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Okólna 2, 50-422 Wrocław, Poland
Resume : Oxygen and water vapor cause irreversible degradation of organic solar cells (OSC’s), being the main factor responsible for the reduction of the shelf lifetime of those devices. Especially vulnerable to degradation are OSC’s produced on thin, elastic polymer substrates such as polyethylene terephthalate (PET), which display very poor barrier properties. Therefore, novel thin layers and coatings need to be developed in order to protect chemically sensitive structure of OSC’s. Water Vapor Transmission Rate (WVTR) as low as 10-5 g/m2d is required to provide sufficient encapsulation and long-term stability of OSC’s. The primary methodology used to evaluate WVTR is based on the electrical calcium test (ECT). In this approach, the resistance of a thin calcium layer, enclosed within investigated barrier material, is constantly monitored. While water molecules diffuse through the barrier, calcium transforms from conductor to insulator. Basing on the rate of this transition, permeability properties of a given material are studied. Here, we present an overview of ECT method developed in our laboratory, which allows for a simultaneous measurement of up to 12 samples. We evaluate barrier properties of sol-gel synthesized silicone dioxide (SiO2) and graphene oxide (GO) single and multilayers prepared on PET substrates with spin-coating method. Silica coating is based on hybrid organic/inorganic materials as precursors. GO is obtained according to modified Hummers method.
Authors : Seçkin AKIN1,2,*, Recep TAŞ3, Erdinç EROL1,2, Muzaffer CAN4, Savaş SÖNMEZOĞLU1,2
Affiliations : 1Department of Metallurgical and Materials Engineering, Karamanoğlu Mehmetbey University, Karaman, Turkey 2Nanotechnology R&D Laboratory, Karamanoğlu Mehmetbey University, Karaman, Turkey 3Department of Chemistry, Gaziosmanpasa University, Tokat, Turkey 4Department of Chemistry, Kırıkkale University, Kırıkkale, Turkey
Resume : Herein, we successfully synthesized zinc-embedded polyaniline (Zn@PAni) using chemical oxidation polymerization and investigated its application as counter electrode (CE) in dye-sensitized solar cells (DSSCs). The experimental results characterized by several methods (SEM/EDAX, XRD, AAS, TGA/DTA, etc.) showed that critical properties such as crystallinity, conductivity and surface area of PAni polymers were controlled through the Zn atoms. It is found from the photovoltaic measurements that the DSSC based on Zn@PAni CE demonstrates the best performance showing an impressive photovoltaic conversion efficiency (PCE) of 8.06% which exceeds the efficiency of a Pt-based DSSC (6.93%), while the DSSC consisting of bare PAni only exhibits a PCE of 4.28%. Such an enhanced efficiency of the DSSC is attributed to the effectively enhanced surface area and improved conductivity resulting from the Zn atoms. To further investigate the electrocatalytic activities of CEs, electrochemical impedance spectroscopy (EIS) and Tafel polarization (TP) analysis have been performed by assembling dummy cells. Consequently, the Zn@PAni is expected to replace the expensive Pt as a promising CE catalyst. Keywords: Dye-sensitized solar cells, Zinc-embedded polyaniline, Counter electrode, Electrocatalytic activities.
Authors : Sebastian Wilken, Dorothea Scheunemann, Holger Borchert, Jürgen Parisi
Affiliations : Energy and Semiconductor Research Laboratory (EHF), Department of Physics, Carl von Ossietzky University of Oldenburg, Carl-von-Ossietzky-Straße 9–11, 26129 Oldenburg, Germany
Resume : The nature of the nongeminate recombination in polymer–fullerene bulk heterojunction solar cells is still subject of ongoing discussion. In particular, there is a lack of a general model taking into account the complex three-dimensional morphology of a phase-separated blend. Here, we present an experimental study on how the competition between collection and recombination of free charges is mediated by the phase separation in the model system of poly(3-hexylthiophene) (P3HT) blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). By varying the evaporation rate of the solvent during deposition, we prepared two different morphologies with average domain sizes of ~6 nm and ~10 nm, respectively, as confirmed by high-resolution electron tomography. Using a combination of steady-state and transient measurement techniques, we show that in case of the coarse phase separation, the recombination is dominated by a Langevin-type process of second order, whereas, in case of the fine phase separation, the relative strength of the direct decay is strongly reduced. Notably, this trend with domain size is opposite to what has recently been predicted by Monte Carlo simulations [Phys. Rev. Lett. 114, 136602 (2015)]. We will discuss our findings with respect to charge carrier trapping in intermixed phases, as well as the possible occurrence of two-dimensional Langevin recombination.
Authors : K. Startek, P. Kozioł, T. Baraniecki, M. Kargol, F. Granek
Affiliations : Wrocław Research Centre EIT , Stabłowicka 147, 54-066 Wrocław, Poland
Resume : UV, oxygen and water diffusion barrier are the main properties required for coating materials to ensure long term stability of the optoelectronic devices, such as solar cells. On the other hand, low-cost optoelectronic devices such as solar cells require protective layers with several functions to maintain a high efficiency during their lifetime that are usually achieved with multilayer coatings, in which one or more layer have a specific functionality. The ideal coating materials require no vacuum processing, and are deposited at high deposition rates and low-cost. In the present research work functional sol−gel based materials are synthesized at room tem-perature via the hydrolysis and polycondensation of precursors such as silicon alkoxides and organically modified metal alkoxide. In our laboratory study, the silica-based layers are de-posited by a spin-coating method on flexible polymeric support. The resulted materials showed excellent flexibility and optical properties. Next, the obtained transparent coating layers are modified by laser radiation to improve lay-ers’ properties. Various parameters for the laser treatment are tested and the obtained coatings layers are characterized by SEM and FT-IR with ATR mode. This work was funded by The National Centre for Research And Development (NCBR) within The Project POSCIS (Grant Agreement No. LIDER/09/129/L-3/11/NCBR/2012.
Authors : Maciej Klein1,2, Sayani Majumdar3, Waldemar Stampor1
Affiliations : 1Department of Physics of Electronic Phenomena Faculty of Applied Physics and Mathematics, Gdansk University of Technology, Narutowicza 11/12, 80-233 Gdansk, Poland; 2Centre for Plasma and Laser Engineering The Szewalski Institute of Fluid-Flow Machinery, Polish Academy of Science Fiszera 14, 80-231 Gdansk, Poland; 3Department of Applied Physics Aalto University School of Science, 00076 Aalto, Finland
Resume : The rapid increase in application of organic materials for manufacturing photovoltaic (PV) cells and electroluminescent (EL) diodes is nowadays accompanied by an intensive research in electrical and optical properties of organic thin films. The charge recombination and exciton dissociation are generally recognized as the basic electronic processes limiting the efficiency of organic EL and PV devices. These processes in low-mobility organic materials are usually assumed to proceed via the intermediate stage of an electron–hole (e-h) pair. If these intermediate species are endowed with the magnetic moment then external magnetic field can interact with them and this way change the generated photocurrent. In this work we show the influence of external magnetic field on a photocurrent (the MPC signal) in squaraine:PCBM organic bulk heterojunction solar cells. Studies were carried out in a wide range of magnetic field (since less than 1 mT up to 9 T) as well as in the function of temperature (200 – 300 K), photon flux and electric field. Depending on PCBM concentration and magnetic field strength the MPC results are ascribed to hyperfine (electron-nucleus) interaction modulation (HFM), fine (electron-electron) structure modulation (FSM) or Δg mechanism determined by different values of Lande g-factor for electron and hole entities forming e-h pairs. This work was supported by the Polish Ministry of Science and Higher Education under “Diamond Grant” 0228/DIA/2013/42.
Authors : P. Kwaśnicki1, M. Inglot2
Affiliations : 1 Research & Development Centre for Photovoltaics, ML System S.A Zaczernie 190 G, 36-062 Zaczernie, Poland, 2 Dpartments of Physics and Medical Engineering, Rzeszów Unieversity of Technology al. Powstańców Warszawy 6, 35-959 Rzeszów, Poland
Resume : Nanoscale materials has attracted grate attention over lasts years due to their suitable properties for many different fields. Low dimensions structure such as quantum dots has also been used in photovoltaic to increase the conversion efficiency and the final performance of solar cells due to its potential to increase the maximum attainable thermodynamic conversion efficiency of solar photon conversion up to about 66% by utilizing hot photogenerated carriers to produce higher photovoltages or higher photocurrents  and also by widening the absorption range of electromagnetic wave. So far many of deposition process have been studied in order to achieve suitable distribution of quantum dots , ,  nonetheless to obtain homogeneous layer not only on the surface but also in depth in a easily scalable process is still of an issue. We propose spin coating as a method of deposition and thermal annealing in low pressure in order to enhance penetration of the quantum dots into porous layer of TiO2. So far the annealing process was mostly us conducted to improve the solar cell performance . The main goal is to find cheap easy scalable method of deposition that can be used for future production process. Depth profile measurement done using Secondary Ion Mass Spectroscopy showed that indeed annealing increase significantly quantum dots penetration in Z axis. Furthermore we also noticed increase in IPCE for samples after thermal process. 1.Prashant V. Kamat et al. J. Phys. Chem. C, 2008, 112 (48), pp 18737–18753 2.J. Mater et al. J. Mater. Chem. A, 2015,3, 12539-12549 3.Yan Zhang et al. Phys. Chem. Chem. Phys., 2011,13, 13182-13184 4.Tracey M. Clarke et al. Advanced Energy Materials Nov., 2011,Vol. 1, Issue 6, p 1169–1175, 5.Yitan Li et al. Journal of Nanomaterials Vol. 2012 ID 103417,
Authors : S. J. Montiel-Perales, J.A. Baron-Miranda, C. Zafiro-Ortega, L. Ponce, C. Guarneros-Aguilar, F. Chalé-Lara, F. Caballero-Briones
Affiliations : S. J. Montiel-Perales; J.A. Baron-Miranda; F. Chalé-Lara; F. Caballero-Briones 1. Instituto Politécnico Nacional, Laboratorio de Materiales Fotovoltaicos, CICATA Altamira. C. Zafiro-Ortega; L. Ponce 2.Instituto Politécnico Nacional, Laboratorio de Tecnología Láser, CICATA Altamira C. Guarneros-Aguilar 3.Consejo Nacional de Ciencia y Tecnología, CONACYT
Resume : CdTe films were prepared onto Cu-cladded boards by pulsed electrodeposition in a two electrode configuration at different pulse frequencies. Commercial graphene oxide solution 0.05 mg/mL was deposited on top of the CdTe films by electrophoretic deposition using the same potential routines. The heterostructures consisted in 10 layers of each material. The structure was studied by X-ray diffraction, the relative composition by laser induced breakdown spectroscopy and the optical absorption by diffuse reflectance. The morphology and local electrical response of the films was studied by current sensing atomic force microscopy and the photocurrent response was studied in the constant wave mode using an indium tin oxide covered glass as counter-electrode. The heterostructures were compared with CdTe films and the results are discussed in terms of the current separation efficiency due to the influence of the graphene oxide interlayer. Novel architectures to incorporate the deposited structures in hybrid solar cells are proposed. FCB and FCL acknowledge financial support from SIP-20161804 multidisciplinary project
Authors : Francisco C. Franco Jr.
Affiliations : Chemistry Department, De La Salle University, 2401 Taft Avenue, 0922 Manila, Philippines
Resume : Organic photovoltaics is now gaining attention due to its various potential commercial advantages, such as, lightweight, easily fabricated, and low-cost devices. In order to improve the conversion efficiencies of organic solar cells, various studies has to be done, and one of which is the study of material design and its intrinsic properties. In this study, the optoelectronic properties of P3HT oligomers were altered via chemical modifications using different substituents and the solar cell characteristics of the modified oligomers were predicted. The optoelectronic properties of various poly(3-hexylthiophene-2,5-diyl) (P3HT) derivatives were investigated via density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Substituents with various acceptor and donor characteristics were attached to the P3HT oligomers. The optoelectronic properties for the polymer derivatives were approximated using the oligomer energy values. The frontier orbitals: EHOMO and ELUMO, and the fundamental energy gap, EGap were calculated using DFT while the first singlet excited state EOpt were calculated using TD-DFT. Results show that the electronic and optical properties of P3HT can be adjusted depending on the substituent attached. Properties relevant to organic solar cells were also investigated: exciton binding energy (EB), ionization potential (IP), and open-circuit voltage (VOC), and were also observed to be influenced by chemical modifications. P3HT-F and P3HT-CN were observed to have better properties: VOC, EGap, and IP compared to the unsubstituted P3HT. Chemical modifications can be a simple and cheap way to vary the intrinsic properties of organic polymers for solar cells.
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Organic solar cells I : Andreas HINSCH
Authors : Silvija Gradecak
Affiliations : Department of Materials Science and Engineering, MIT
Resume : Emerging PV devices based on solution-processable materials offer opportunities for the production of low-cost solar cells. To obtain high efficiencies of exciton dissociation and high photocurrent, it is desirable to have an interpenetrating network of electron-donor and electron-acceptor components within the device, referred to as a bulk heterojunction (BHJ). However, current limitations of these devices are inefficient hopping charge transport through the discontinuous percolation pathways in the BHJ films, and therefore modest power conversion efficiencies or non-competitive cost. We have developed an alternative type of nanowire-based solar cells that are based on organic/inorganic hybrid device structures and demonstrated two distinct hybrid BHJ architectures with enhanced power conversion efficiencies. Furthermore, we have developed a simple method to grow high-quality ZnO nanowires on graphene via the hydrothermal method. Based on the graphene/ZnO nanowire structure, we have demonstrated graphene cathode-based hybrid solar cells by using two different solution-processed photoactive materials – PbS quantum dots (QDs) and poly(3-hexylthiophene) (P3HT) conjugated polymers – and ZnO nanowires as hole and electron transport layers, respectively. We have also identified several critical parameters to further boost the device efficiency and enable scalable, cost-efficient production, and these will be discussed. In another example, the impact of microscale film inhomogeneities on performance of organic-inorganic perovskite solar cells (PSCs) remains poorly understood, despite the recent astronomical success of this class of PV devices. We show that localized regions with increased luminescence in CH3NH3PbI3 perovskite films correspond to iodide-enriched regions. These observations constitute direct evidence that nanoscale stoichiometric variations produce corresponding inhomogeneities in film luminescence intensity. Moreover, we observe the emergence of high-energy transitions attributed to beam induced iodide segregation, which may mirror the effects of ion migration during PSC operation. Our results address the observed complex behavior in PSC devices.
Authors : Zhan, Chuanlang
Affiliations : Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, P.R. China
Resume : Bulk-heterojunction organic solar cell (BHJ-OSC) utilizes a nanostructured electron donor and electron acceptorblended film to capture and convert solar photons into electrons. Recently, much attention has been focused on non-fullerene organic acceptors, which are used as acceptor materials to replace the traditional fullerene acceptor materials. The exciton-type photon-to-electron conversion efficiencies such as exciton generation and charge separation and transport are largely dependnet on the material absorption, frontier molecular orbitals and film-morphology. In this report, I will show our group’s results on the molecular strategies towards efficient small-molecule photovoltaic materials. The results include (1) the photovoltaic properties from the twisted perylene-dimide dimer acceptors, (2) the photovotaic properties from BODIPy based small molecule donor and acceptor, and (3) the photovoltaic properties from diketopyrrolopyrrole (DPP) and Quinoidal Methyl-Dioxocyano-Pyridine based small molecule donors, in particular, the effects of the end units capping on the DPP mainchain and the influences from the anchoring groups terminated on the flexible alkyl chains. References: 1. Chuanlang Zhan, and Jiannian Yao, Chem. Mater. 2016, 28 (7), 1948-1964. 2. Chuanlang Zhan, and Xinliang Zhang, and Jiannian Yao, RSC Adv. 2015, 5(113), 93002 - 93026 3. Ailing Tang, Chuanlang Zhan, Jiannian Yao, Chem. Mater. 2015, 27 (13), 4719-4730. 4. Ailing Tang, Chuanlang Zhan, and Jiannian Yao, Adv. Energy Mater. 2015, 5(13), 1500059. 5. Yuxia Chen, Xin Zhang, Chuanlang Zhan, and Jiannian Yao, ACS Appl. Mater. Interface, 2015, 7 (12), 6462 – 6471. 6. Xin Zhang, Chuanlang Zhan and Jiannian Yao, Chem. Mater. 2015, 27 (1), 166-173. 7. Wenxu Liu, Ailing Tang, Chuanlang Zhan, and Jiannian Yao, ACS Appl. Mater. Interface 2014, 6 (24), 22496 – 22505. 8. Zhenhuan Lu, Bo Jiang, Xin Zhang, Ailing Tang, Lili Chen, Chuanlang Zhan and Jiannian Yao, Chem. Mater. 2014, 26 (9), 2907-2914. 9. Xin Zhang, Zhenhuan Lu, Long Ye, Chuanlang Zhan, JianhuiHou, Shaoqing Zhang, Bo Jiang, Yan Zhao, Jianhua Huang, Shanlin Zhang, Yang Liu, Qiang Shi, Yunqi Liu, and Jiannian Yao, Adv. Mater. 2013, 25 (40), 5791-5797.
Authors : Joana Farinhas a), Ricardo Oliveira a), Quirina Ferreira a), Jurgen Kesters b), Dirk Vanderzande b), Wouter Maes b), Ana Charas a), Jorge Morgado a,c)
Affiliations : a) Instituto de Telecomunicações, Avenida Rovisco Pais, P-1049-001 Lisboa, Portugal b) Institute for Materials Research (IMO), Hasselt University, Agoralaan 1–Building D, B-3590 Diepenbeek, Belgium c) Department of Bioengineering, Instituto Superior Técnico, Universidade de Lisboa, Avenida Rovisco Pais, P-1049-001 Lisboa, Portugal E-mail: email@example.com
Resume : The use of selective charge extraction/blocking layers has allowed significant improvements of bulk heterojunction organic solar cells performance. We have been investigating the use of a phenantroline derivative, BPhen, as electron-extraction layer and found that it leads to improvements of power conversion efficiencies, for some polymers, in particular when LiF/Al low workfunction electrodes as used. In addition, we found that the deposition of BPhen by thermal evaporation over the polymer:PCBM films leads, in general, to nanostructured films, as shown by AFM analysis, with rather tall motives in comparison to the average thickness. In this communication we present results of efficiency and BPhen films morphology for various polymers and different surface PCBM contents. Acknowledgments: We thank FCT Portugal for financial support under the contracts M-ERA.NET/0001/2012, UID/EEA/50008/2013 and UID/NAN/50024/2013 and for a PhD grant to Joana Farinhas.
Authors : Dong Chan Lim
Affiliations : urface Technology Division, Korea Institute of Materials Science (KIMS), Changwon, R.O. Korea
Resume : Polymer bulk heterojunction (BHJ) solar cells based on composites of semiconducting conjugated polymers and soluble fullerene derivatives have received much attention because of their potential application in low-cost, printable, portable, and flexible renewable energy sources even though low power conversion efficiency. Insufficient solar light absorption is usually considered to be a crucial hindrance for BHJ solar cells towards achieving higher efficiency. Several light trapping approaches, such as diffraction gratings, photonic crystals, and surface plasmon resonance (SPR), have been investigated and have been demonstrated to increase the light absorption of organic thin films. Among these, utilizing SPR effects with various metal nanoparticles (NPs) like Au or Ag NPs in a few tens of nm-meter size has been the most successful approach. In this work, we have incorporated glutathione (GSH) monolayer-protected Au nanoclusters (Au:SR) with sub-nm-sized Au38 cores on inverted BHJ solar cells, instead of tens of nm-sized metal NPs. Because of effective energy transfer, based on protoplasmonic fluorescence of Au:SR, the highest performing solar cells, ~20% increase in the efficiency, fabricated with the Au:SR cluster.  In addition, the solar cell with Au:SR nanocluster showed more stable performance under light soaking condition.
Organic solar cells II : Masayuki CHIKAMATSU
Authors : U. Würfel, A. Spies, M. List, M. Kohlstädt
Affiliations : Fraunhofer Institute for Solar Energy Systems ISE Heidenhofstr. 2, 79110 Freiburg, Germany; Freiburg Materials Research Center FMF, Albert-Ludwigs-University Freiburg, Germany
Resume : Organic semiconductors used in the photoactive layer of organic solar cells usually comprise rather low charge carrier mobilities. Under current flow this can lead to considerable accumulation of charge carriers causing enhanced recombination. An important consequence is that the voltage applied at the contacts does not equal the voltage inside the photoactive layer. For this reason the current-voltage characteristics of such a transport-limited solar cell differs significantly from the the well-known Shockley diode equation. A model will be presented which considers the effect of limited mobility explicitly and which allows to determine the correct value for the voltage required for the application of the Shockley equation . In addition, the model can be used to evaluate efficiency potentials in a more realistic manner. Surface recombination is a loss mechanism in addition to the recombination (radiative and non-radiative) in the bulk of the photoactive layer . To minimize it in organic solar cells charge carrier selective layers are used between the photoactive layer and the electrode. These layers (e.g. PEDOT:PSS, TiOx, ZnO, WoOx, MoOx) often have a rather large band gap and thus can block the “wrong” type of charge carrier quite efficiently. However, surface states within the band gap of these materials at the interface with the photoactive layer can still act as recombination centers. Recently, there are numerous examples of polar (organic) molecules providing a high degree of charge carrier selectivity, one prominent example being the work of He et al. on PFN . Some of these materials are however rather expensive. We used simple, harmless, extremely cheap and easy-to-process organic molecules with permanent dipole moments. These molecules alter the effective work function of the electrode as confirmed by scanning Kelvin probe force microscopy and ultraviolet photoelectron spectroscopy (UPS) which revealed a corresponding shift of the surface potential. This leads to a strong increase (decrease) of the electron (hole) concentration in the adjacent photoactive layer. It will be shown in detail that this is the main reason for the enhanced selectivity causing an increase of the open-circuit voltage (and fill factor) for different photoactive layers. A theoretical model was set up and the results of the numerical simulations are in full accordance with the experimental data. Interestingly, DFT-calculations prove that the energy levels of the dipole molecules used are not suited to conduct charge carriers from the photoactive layer to the electrode but that a tunneling mechanism is involved. Implementing this into our model, it is found that there is no necessity to assume preferential tunneling for electrons. Their accumulation and the depletion of holes due to the altered work function are sufficient to explain the observed behavior .  U. Würfel, D. Neher, A. Spies, S. Albrecht: "Impact of charge transport on current-voltage characteristics and power conversion efficiency of organic solar cells", Nature Communications 2015, 6, 6951.  J. Reinhardt, M. Grein, C. Bühler, M. Schubert and U. Würfel: "Identifying the Impact of Surface Recombination at Electrodes in Organic Solar Cells by Means of Electroluminescence and Modeling", Advanced Energy Materials, 2014, 4, 1400081.  Z. He, C. Zhong, X. Huang, W.-Y. Wong, H. Wu, L. Chen, S. Su, Y. Cao, Advanced Materials 2011, 23, 4636  U. Würfel et al. "How Molecules with Dipole Moments Enhance the Selectivity of Electrodes in Organic Solar Cells - a Combined Experimental and Theoretical Approach", under review.
Authors : Feng Yan
Affiliations : Department of Applied Physics, The Hong Kong Polytechnic University
Resume : High-performance organic solar cells have been developed by our group based on various nanotechnology in recent years. First, the efficiency of organic solar cells have been improved by introducing plasmonic nanoparticles, high mobility conjugated polymers or 2-D materials. Pronounced effects have been observed in the devices due to the improvement of the carrier mobility or light absorption in the active layer. Graphene has shown promising applications in photovoltaic devices for its high carrier mobility and conductivity, high transparency, excellent mechanical flexibility and ultrathin thickness and can be used in solar cells as transparent electrodes or interfacial layers. Package-free flexible organic solar cells are fabricated with multilayer graphene as top transparent electrodes, which show high power conversion efficiency, excellent flexibility and bending stability. Semi-transparent organic solar cells and perovskite solar cells were prepared by using graphene transparent electrodes. For the perovskite solar cells, the devices show high power conversion efficiencies (~12%) when they are illuminated from both sides. Considering the poor stability of perovskite solar cells in ambient air especially with high humidity, we have recently developed a novel technique to improve the device stability by introducing SCN- to partially replace I- in the perovskite material, which can dramatically improve the lifetime of package-free device in air. All of the techniques will be very useful for the practical applications of the novel photovoltaic devices.
Authors : Quyet Van Le, Soo Young Kim*
Affiliations : School of Chemical Engineering and Materials Science, Chung-Ang University, 84 Heukseok-ro, Dongjak-gu, Seoul 06974, Republic of Korea
Resume : Inorganic material such as MoS2, WS2, TaS2 (MeSx), WOx, and graphene oxide (GO) were successfully applied as hole extraction layer (HEL) for organic photovoltaic cells (OPVs). WOx thin film was obtained via thermal decomposition of (NH4)2WS4 under air ambient condition. Whereas MeSx was obtained through the ultra-sonication method and GO was fabricated by Hummer’s method. The WOx layer which was obtained by thermal decomposition at 160 oC shows smooth surface (~ 2 nm) as well as high work function (~ 5 eV), resulting OPVs with high power conversion efficiency of 3.14 %. On the contrary, the synchrotron radiation photoelectron spectroscopy data show that the work functions (WFs) of pristine MeSx and GO are relatively low (WFMoS2 = 4.6 eV, WFWS2 = 4.9 eV, WFTaS2 = 4.4 eV, WFMoS2 = 4.4 eV, WFGO = 4.8 eV), indicating that they are not suitable for the use as HELs in organic photovoltaic cells. The power conversion efficiency of OPVs with MoS2, WS2, TaS2 and GO as HELs are 1.08, 1.84, 0.01, 2.06 %, respectively. The WFs of MeS2 were then modified using UV-ozone (UVO) treatment while the WF of GO was modulated through the silane-functionalization. Upon UVO treatment for a certain time (15 – 30 min) for MeS2 or silane-functionalization for graphene (SF-Gr), the WF of MeSx as well as GO increased up to approximately 5 eV which are comparable to that of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The increment in WF of MeS2 and GO lead to increase of OPVs power conversion efficiency (PCE = 2.44, 2.4, 3.06, 3 % with UVO-MoS2, UVO-WS2, UVO-TaS2 and SF-Gr as HELs, accordingly). These results provide a versatile method for the fabrication HEL to replace highly hygroscopic PEDPT:PSS in terms of high efficiency and stability.
Organic solar cells III : Filippo DE ANGELIS
Authors : Carl Poelking, Max Tietze, Chris Elschner, Selina Olthof, Dirk Hertel, Bjoern Baumeier, Frank Würthner, Klaus Meerholz, Karl Leo, Denis Andrienko
Affiliations : Max Planck Institute for Polymer Research
Resume : We will discuss the role of mesoscale order, electrostatic effects, defects, and roughness for charge splitting and detrapping at donor-acceptor interfaces. We will show how inclusion of mesoscale order resolves the controversy between experimental and theoretical results for the energy-level profile and alignment in a variety of photovoltaic systems, with direct experimental validation. We predict open-circuit voltages of planar heterojunction solar cells in excellent agreement with experimental data, based only on crystal structures and interfacial orientation. We show how long-range molecular order and interfacial mixing generate homogeneous electrostatic forces that can drive charge separation and prevent minority carrier trapping across a donor-acceptor interphase. Comparing a variety of small-molecule donor-fullerene combinations, we illustrate how tuning of molecular orientation and interfacial mixing leads to a trade-off between photovoltaic gap and charge-splitting and detrapping forces, with consequences for the design of efficient photovoltaic devices.  C. Poelking, M. Tietze, C. Elschner, S. Olthof, D. Hertel, B. Baumeier, F. Wuerthner, K. Meerholz, K. Leo, D. Andrienko, Nature Materials, 14, 434-439, 2015  C. Poelking, D. Andrienko, J. Am. Chem. Soc., 137, 6320-6326, 2015  M. Schwarze, W. Tress, B. Beyer, F. Gao, R. Scholz, C. Poelking, K. Ortstein, A. A. Guenther, D. Kasemann, D. Andrienko, K. Leo, Science, 2016
Authors : Itaru Osaka
Affiliations : RIKEN, Center for Emergent Matter Science
Resume : Improvement of power conversion efficiencies (PCEs) is one of the largest issues in polymer-based solar cells (PSCs). A number of new semiconducting polymers with donor–acceptor (D–A) backbones have been developed in the past decade. In this presentation, I will introduce new D–A semiconducting polymers incorporating acceptor π-bulding units, naphthobisthiadiazole (NTz) and naphthobisoxadiazole (NOz). NTz gave polymers with narrow band gaps (1.5–1.6 eV) and relatively large ionization potentials (~5.2 eV). It is also mentioned that the NTz-based polymers showed quite high crystallinity along with the face-on backbone orientation suitable for solar cells. As a result, one of the NTz-based polymers, PNTz4T, demonstrated PCEs as high as 10% in single-junction solar cells. On the other hand, NOz gave polymers with larger ionization potentials of around 5.5 eV than the NTz analogues, while having the similar band gaps. Interestingly, an NOz-based polymer, PNOz4T, afforded high PCEs of up to 8.9% with very high open-circuit voltages of ~1 V in solar cells. Thus, the photon energy loss of the cells was found to be 0.52–0.55 eV, which was reduced by ca. 0.3 eV from that of the cells using the NTz-polymers and was very small compared with the typical value for PSCs (0.7–0.8 eV). These unconventional features in PNOz4T originate in the fact that the photoinduced electron transfer between the NOz-polymer and fulluerene occurs even though the offset energy of LUMOs is ~0.1 eV, which is significantly less than the widely referenced threshold value of 0.3 eV. These results indicate that NTz and NOz are indeed fascinating building units for the development of high-performance semiconducting polymers for PSCs.
Authors : David M. Huang, Patrick C. Tapping, Kyra N. Schwarz, Simon J. Blacket, Scott N. Clafton, Tak W. Kee
Affiliations : Department of Chemistry, The University of Adelaide, Adelaide, SA 5005, Australia
Resume : Organic semiconductors have wide-ranging applications, from photovoltaics and solid-state lighting to biological imaging. But rational design of organic semiconductor materials and devices remains a challenge, as these materials are typically highly disordered, while structural and functional electronics are strongly coupled over many length scales in devices. This presentation discusses our recent work developing and applying accurate multi-scale computational models  that combine physical and electronic structure, in order to understand the role of physical structure and dynamics on fundamental processes in organic electronics, specifically energy transfer , singlet fission, and triplet-triplet annihilation. Model accuracy is verified by comparing predictions with time-resolved spectroscopic measurements. References:  K.N. Schwarz, T.W. Kee, D.M. Huang, Nanoscale 5, 2017-2027 (2013).  P.C. Tapping, S.N. Clafton, K.N. Schwarz, T.W. Kee, D.M. Huang, Phys. Chem. C 119, 7047-7059 (2015).
Authors : John Grey
Affiliations : Department of Chemistry and Center for High Technology Materials (CHTM) Associate Director, Nanoscience and Microsystems program University of New Mexico MSC03 2060 Albuquerque, NM 87131
Resume : We demonstrate that, in the limit, of large exciton coherence lengths, spin-forbidden triplet excitons can form via non-traditional pathways, namely, charge transfer state intermediates. Electric field dependent, time-resolved single molecule spectroscopy approaches are used to interrogate the presence and roles of charge transfer states in self-assembled aggregate nanofibers of poly(3-hexylthiophene) (P3HT). Importantly, this process allows only the high molecular weight fraction to self-fold into aggregated structures which suppresses typical exciton localization on sub-ps time scales. The resulting delocalized intrachain singlet excitons have a greater likelihood of encountering interchain charge transfer states owing to their longer lifetimes. Once a charge transfer state is populated, separated, and uncorrelated, carriers, may recombine on longer time scales preferentially to triplet excitons. We further demonstrate that the density of charge transfer states depends on the size of the nanofiber (i.e., number of self-folded chains) suggesting interchain contacts as the structural origins of these states. By selectively controlling formation kinetics of hierarchical organic polymer assemblies, we have demonstrated the ability to direct photophysical outcomes in these intrinsically disordered and stochastic materials.
Hybrid solar cells : Konrad WOJCIECHOWSKI
Authors : Joel Jean
Affiliations : Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology
Resume : Solar photovoltaics (PV) are the fastest-growing energy technology today and a leading candidate for terawatt-scale, carbon-free electricity generation by 2050. Commercial PV module prices have declined rapidly, but balance-of-system (BOS) costs remain high. Further cost reductions are needed to compensate for the declining value of intermittent solar power with increasing grid penetration. Emerging thin-film PV technologies such as perovskites, organics, and colloidal quantum dots open the door to new deployment formats today and could ultimately reach materials, processing, and deployment cost floors inaccessible with conventional technologies. In this talk, I will discuss potential limitations to scaling up PV deployment, emphasizing constraints on the use of commodity and PV-critical materials. I will introduce material complexity as a framework for classifying commercial and emerging PV technologies, and identify strategies to realize the unique advantages of solar PV as a room-temperature, noiseless, modular, seamlessly integrated, and mechanically imperceptible power source.
Authors : H. M. Thirimanne, K. D. I. Jayawardena, J. V. Anguita, V. Stolojan, E. New, C. A. Mills, S. R. P. Silva
Affiliations : Advanced Technology Institute, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford, Surrey, GU2 7XH, UK
Resume : Efficient charge extraction is a crucial point in many semiconductor devices. Here, we introduce a new device concept for flexible platforms; structured electrodes that can be used for improved charge extraction, enabled via charge funnelling. We further demonstrate how the concept can be used in multiple applications, such as solar cells and real-time solid state X-ray detectors. This study focuses on developing this novel concept using an organic solar cell as a representative application where the nanostructured back contact leads to an overall 30% efficiency gain. Insulating bismuth oxide (Bi2O3) nanoparticles are used to structure the cathode contact in a standard polymer solar cell, with the aim of creating a localized geometric electric field enhancement. As Bi has a high X-ray attenuation coefficient, this has a high significance on X-ray detectors as well. The presence of the insulating nanoparticles leads to the formation of a device which operates under short circuit conditions. This feature, when combined with the field enhancement, allows for the extraction of currents (which are at the short circuit condition) under maximum power point conditions. The efficient extraction of charges is determined by the size of the Bi2O3 nanoparticles, and the tuning of the dimensions is shown to be a requirement in order to achieve optimum performance. Compared to a non-structured metal back contact, this solution-based structuring of the metal back contact results in an electric field enhancement in charge extraction and leads to an efficiency improvement of 30%. The novel device concept proposed here forms a new route for efficient charge funnelling via the nanostructured contacts, which could be extended into many device platforms.
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Theory and processes in organic solar cells I : Denis ANDRIENKO
Authors : Ning Li, Christoph J. Brabec
Affiliations : N. Li; C. J. Brabec; Institute of Materials for Electronics and Energy Technology (i-MEET), Friedrich-Alexander University Erlangen-Nürnberg, Martensstrasse 7, 91058 Erlangen, Germany. C. J. Brabec; Bavarian Center for Applied Energy Research (ZAE Bayern), Haberstrasse 2a, 91058 Erlangen, Germany.
Resume : Tremendous progress has been made in the field of organic photovoltaics (OPV) in the last few years, and the power conversion efficiencies (PCEs) of organic solar cells (OSCs) were steadily improved to the 11% regime. To push the OPV technology towards commercial applications, the reliability and stability of champion OPV devices have to be examined. The performance of OSCs is determined by the delicate, optimized bulk-heterojunction (BHJ) microstructure, where the organic donor and acceptor are fine-mixed in the nano-meter regime to facilitate exciton dissociation at the donor / acceptor interface. In this contribution, we will examine the reliability and stability of BHJ microstructures for various state-of-the-art solution-processed OSCs and explore their potential for large-scale mass production. Strategies to design and develop BHJ microstructures with promising stability will be discussed. Moreover, novel organic acceptors based on fullerene derivatives and non-fullerene molecules are developed and analysed for state-of-the-art organic donors to simultaneously reduce their sub-transmission losses and bandgap to VOC losses. Recent results on novel organic acceptors-based OSCs will be in-depth discussed in this work.
Authors : Michał Wrzecionek (1), Paulina Hibner- Kulicka (3), Tomasz Plocinski (2), Dorota Brzuska-Kamoda (1), Karolina Pietak (1), Grzegorz Matyszczak (1), Daniel Jastrzebski (1), Maciej Bialoglowski (1), Jacek Ulanski (3), Slawomir Podsiadlo (1)
Affiliations : (1) Faculty of Chemistry, Warsaw University of Technology; Noakowskiego 3, 00-664 Warsaw, Poland (2) Faculty of Materials Engineering, Warsaw University of Technology, Wołoska 141, 02-0507, Warsaw, Poland (3) Department of Chemistry, Lodz University of Technology, Zeromskiego 116, 90-924, Lodz, Poland
Resume : Nowadays scientists from around the world are looking for solution of high energy consumption, which also will be friendly for environment and available for average earning people (low costs of production). Photovoltaics is a major area of research within the field of renewable energy sources. Organic Photovoltaic Cells (OPV) are an alternative for Si-cells, CIGS, CdSe-cells, and others including expensive and toxic materials, but their energy conversion is smaller. Kesterite Cu2ZnSnS4 can be functionalized with organic ligand and dedicated for selected semiconducting polymers, what allows created new hybrid solar cells, which works with better efficiency. The obtained materials have been characterized with X-ray methods, transmission electron microscopy and spectrophotometry UV/Vis/NIR.
Authors : Guanran Zhang, Tracey Clarke, Attila Mozer
Affiliations : Intelligent Polymer Research Institute, University of Wollongong, Wollongong, 2522, AU; Department of Chemistry, University College London, London, WC1H 0AJ, UK
Resume : Increasing molecular weight (Mw) of conjugated polymers as electron donor has been reported to improve solar cell performance in a number of polymer: PCBM bulk heterojunction systems, the reason of which has been attributed to the change in film morphology as a result of changing molecular weight. However, further study correlating such morphological change with photo-physics of operating devices, more specifically the bimolecular recombination kinetics of photo-generated charge carriers, is scarce. Here, bimolecular recombination in a low bandgap polymer DT-PDPP2T-TT: PCBM bulk heterojunction solar cell is found reduced (Langevin prefactor decreasing from 0.27 to 0.07) when the polymer Mw is increased from 33kDa to 80kDa. The bimolecular recombination in the high and low Mw DT-PDPP2T-TT: PCBM devices were compared using charge extraction using a nanosecond switch, combined with charge extraction by linearly increasing voltage and bulk generation time-of-flight techniques. The study revealed a high charge carrier mobility of 2.39×10-3 cm2V-1s-1 in high Mw device, which is over an order of magnitude higher than that in the low Mw device. The bimolecular recombination coefficient normalized to mobility is four times lower in the high Mw device compared to the low Mw device. The reduced bimolecular recombination, along with the fast charge carrier transport due to the high mobility, explains the high performance achieved in the high Mw device with active layer thickness of 250 nm. Such molecular weight dependence of reduced-bimolecular recombination could be explained by the presence of energetic barrier between the amorphous and crystalline phase of the polymer: PCBM blend, which could be tuned by increasing the molecular weight of the donor polymer. Grazing-incident wide-angle X-ray scattering (GIWAXS) and transient absorption spectroscopy will be performed to examine the hypothesis.
Authors : Alexis Fradon, Eric Cloutet, Georges Hadziioannou, Frédéric Castet, Cyril Brochon
Affiliations : Alexis Fradon; Eric Cloutet; Georges Hadziioannou; Cyril Brochon Laboratoire de Chimie des Polymères Organiques, Allée Geoffroy Saint Hilaire, Bâtiment B8, 33615 Pessac Cedex, FRANCE Alexis Fradon; Frédéric Castet Institut des Sciences Moléculaires, 351 cours de la Libération, Bâtiment. A12, 33405 Talence cedex, FRANCE
Resume : During the last decade, a new kind of donor polymers for photovoltaic application have been intensively studied, the low band-gap polymers. They are based on repeating units associating two different moieties, one electron-rich (ER) and one electron-poor (EP), which allow to finely tune the molecular orbitals and to induce a delocalization of the exciton generated upon the photo-excitation process. A large variety of devices are based on such low band-gap polymers, with a power conversion efficiency record around 10%, and, to increase the efficiency, it is necessary to have a better understanding of these polymers during the photo-absorption phenomenon. To do that, computational chemistry is a powerful tool that permits to predict different opto-electronic properties. For this work, we used Density Functional Theory and Time-Dependent Density Functional Theory to compute the optical properties of increasingly large oligomers involving various ER and EP subunits. The optical properties in the polymer limit were then estimated for the different systems by using an extrapolation scheme based on the Kuhn equation(1). This theoretical screening allowed us to select promising candidates for syntheses, which were performed by a Stille coupling. The obtained polymers and size-controlled oligomers were further characterized by UV-visible spectroscopy, fluorescence, size exclusion chromatography and NMR, in order to extract structure-properties relationships(2) and correlate experimental results to theoretical data. (1) Wykes, M.; Milián-Medina, B.; Gierschner, J. Frontiers in Chemistry 2013, 1, 35. (2) Oriou, J.; Ng, F.; Hadziioannou, G.; Brochon, C.; Cloutet, E. Journal of Polymer Science, Part A: Polymer Chemistry 2015, 53, 2059.
Theory and processes in organic solar cells II : Uli WÜRFEL
Authors : M.L. Petrus, R.K.M. Bouwer, J.C. Bijleveld, T.J. Dingemans
Affiliations : Delft University of Technology
Resume : Materials for organic or Perovskite-based solar cells typically require multi-step expensive synthetic routes. Alternatively, we have been considering step-growth, or (poly)condensation, chemistries as they offer easy access to large quantities of photoactive material without the need for expensive catalysts and workup procedures. Here we present an overview of organic materials based on Schiff Base and imide chemistries studied in our group over the last 10 years. Schiff base chemistry is a cheap and environmentally benign route towards producing p-type materials for organic photovoltaic cells as well as hole conducting materials for perovskite cells. Polymers based on azomethine and triphenylamine monomers in combination with PCBM are shown to have efficiencies exceeding 0.2%. Using small molecule derivatives, azomethine-based materials may reach 2.2% efficiency in an organic solar cell. We also demonstrated that azomethine-based materials are suitable as hole-conducting material in Perovskite-based solar cells reaching similar performance as SpiroOMeTAD (~11%), but at a much lower price. In addition to azomethines, a series of small molecule diimides and their performance in organic photovoltaic cells will be discussed. Changing substituents on the diimide core also changes the solar cell from p-type to n-type. Efficiencies exceeding 0.2% were obtained for PCBM-based devices and 0.5% for P3HT-based devices. Our work shows that there is potential for small molecules azomethines and imides as materials for organic solar cells. The thermal and morphological properties are tunable and their synthesis is easy, cheap and amendable to kg quantity scale-up.
Authors : Catherine Simpson, Tracey M. Clarke, Rowan W. MacQueen, Yuen Yap Cheng, Adam J. Trevitt, Attila J. Mozer, Pawel Wagner, Timothy W. Schmidt, Andrew Nattestad
Affiliations : a. School of Chemistry, The University of Wollongong, Wollongong, NSW 2522, Australia. b. ARC Centre of Excellence for Electromaterials Science (ACES), Intelligent Polymer Research Institute (IPRI), The University of Wollongong, Wollongong, NSW 2522, Australia c. School of Chemistry, University of New South Wales, Sydney 2052, Australia.
Resume : One of the biggest challenges for emerging, organic materials based, solar technologies is to utilise red and near infrared light in ways that don't have deleterious effects on the device open circuit voltage. The device reported here largely resembles a conventional Dye-Sensitised Solar Cell, however two different dyes are employed. One, a functionalised BPEA (BDCA), grafted to TiO2, absorbs high energy photons and injects charge, as per thousands of previous examples of DSCs. A Pt-porphyrin dye, also present, absorbs low energy photons. The energy from these photons is combined (as described below) to realise a novel pathway for current generation, in a two photon process. Photoexcited porphyrins undergo intersystem crossing (ISC) from S1 to T1, which is both fast and results in only a small energy loss. The T1 porphyrin can transfer its energy (Triplet Energy Transfer - TET) to the bound dye, allowing it to enter its T1 state. As two of these T1 state molecules come into proximity they can undergo Triplet-Triplet Annihilation (TTA), which can yield a high energy S1 molecule, capable of injecting an electron into TiO2.
Authors : Oliver Langmar (a),Carolina R. Ganivet (b),Tomás Torres (b),Rubén D. Costa (a),Dirk M. Guldi (a)
Affiliations : (a) Department of Physical Chemistry and Pharmacy & Cluster of Excellence Engineering of Advanced Materials (EAM), Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 3, 91058 Erlangen, Germany; (b) Universidad Autónoma de Madrid, C/Francisco Tomás y Valiente 7, 28049 Madrid, Spain
Resume : Since 1999, Nickel(II)oxide (NiO) has been the electrode material of choice in p-type dye-sensitized solar cells (p-type DSSCs). However, drawbacks such as the inability to produce thick and mechanical stable films, low conductivity, unsuitable valence band energies hindering high open-circuit voltages (Voc) and parasitic light absorption by NiO call for a paradigm shift. In particular, copper(I)delafossites (CuXO2) with X = Chromium (Cr), Gallium (Ga), or Aluminum (Al), emerged as a new class of materials due to their excellent transmission features, high conductivities, and lower valence band energies yielding a higher Voc. Major issues are the expensive synthesis methods, such as hydrothermal or high temperature solid-state synthesis, and the relatively large particle size produced by these methods, which limits dye loading. As an alternative, we focused on the long overlooked copper(II)oxide (CuO), which shows comparable valence band energies, a higher conductivity and charge carrier mobility compared to NiO, and a rich selection of synthesis methods to prepare nanoparticles in all sizes and shapes. Herein, we present p-type DSSCs consisting of CuO-based photocathodes in combination with a novel electron-accepting phthalocyanines sensitizer. By optimization of a number of key factors, such as the calcination temperature, electrode thickness, and iodine/iodide electrolyte ratio, efficiencies of 0.11% have been achieved. The latter are one order of magnitude higher than state-of-the art CuO-based DSSCs of 0.011%. The above-mentioned optimization is supported by electrochemical impedance spectroscopy assays monitoring the changes in injection and recombination processes. Overall, our current work demonstrates that CuO-based photocathodes can be implemented in p-type DSSCs and are competitive to the newly developed delafossite-based devices. References:  F. Odobel et al., J. Phys. Chem. Lett., 4, 2551 – 2564 (2013).  M. Yu et al., Phys. Chem. Chem. Phys., 16, 5026 – 5033 (2014).  Q. Zhang et al., Prog. Mater. Sci., 60, 208 – 337 (2014).  O. Langmar et al., Angew. Chem., Int. Ed., 54, 7688 – 7692 (2015).  S. Sumikura et al., J. Photochem. Photobiol., A, 194, 143 – 147 (2008).
Authors : Mona Sedighi(1), Markus Löffler(1), Falk Röder(2), Ehrenfried Zschech(1,3)
Affiliations : (1) Dresden Center for Nanoanalysis, Center for Advancing Electronics Dresden (cfaed), Technische Universität Dresden, Germany; (2) Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, Dresden, Germany; (3)Fraunhofer-Institut für Keramische Technologien und Systeme (IKTS), Dresden, Germany
Resume : To increase the efficiency of bulk heterojunctions for organic photovoltaic devices, the complicated photon-to-electron conversion process has to be understood in detail. To this aim, one challenge is to resolve the correlation between processing parameters of organic solar cells (OSC), the resulting nanoscale morphology of the absorber layer, and efficiency of the completed device. Here, we present the effect of substrate heating on the morphology of the OSC where the active layer is a blend of two small molecules; ZnPc (ZnC32H18N8) as donor and C60 as acceptor. Obtaining insights into the morphology of the active layer requires the spatial resolution and a contrast mechanism to discriminate two phases with the similar average atomic number. To tackle this challenge, we combine electron microscopy imaging with different analytical techniques; energy dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS) in TEM, as well as Energy selective Backscattered (EsB) imaging in SEM. We imaged different phases of the donor and acceptor, forming ordered and non-ordered regions, depending on the way the heterojunction is fabricated. To this aim, we fabricated samples at substrate temperatures of 110°C and 150°C, each in two different configurations: 1) Focused ion beam prepared ultrathin lamella of a complete solar cell stack with glass substrate, Indium tine oxide (ITO) electrode, ZnPc:C60 blend of the active layer between electron and hole transport layers and aluminum top electrode. 2) Plane view sample as ZnPc:C60 blend deposited on a TEM grid coated with ITO layer. It was shown that at a substrate temperature of 110°C, the solar cell device has high efficiency ., so we consider this as the optimum substrate temperature. Since identification of the composition of each phase in the plane view sample is more straight forward, we use the plane view sample to attribute each structure to one component of the blend. SEM images recorded by using secondary electron detector show that the high temperature sample consists of rod-like features and cube-shaped material in between the rods. By combination of analytical microscopy techniques, we can attribute the rod-like structures to ZnPc. An energy-selective backscatter (EsB) electron detector in SEM is used to obtain backscattered contrast of the plane view sample. Due to the atomic number difference between the donor phase and the acceptor phase, (the average atomic number of 8.6 for ZnPc and 6 for the C60) sufficient contrast can be achieved . A clear confirmation for the attribution of the ZnPc phase to the rod-like features and the attribution of C60 to the granular structure in between can be drawn from the investigation of the sample in SEM using EDX and with even higher precision in TEM using an improved EDX system. The chemical mapping of zinc and carbon, proves the correct phase assignment, in both plane view and ultrathin samples, prepared at high temperature. For the sample produced at optimum temperature, a much smaller roughness was observed because of the absence of large ordered regions. Even in the plane view sample, the imaging contrast is low due to less separated phases and smaller domains. To conclude, we clearly resolved the phase morphology of the interpenetrating network of ZnPc:C60 blends for high and optimum temperature samples in plane view and furthermore we were even able to reveal the morphology from TEM images of cross-section lamellas of the real solar cell stacks. Since the ideal active layer should have domain sizes at the range of the exciton diffusion length (10-20nm), the sample produced at high temperature does not show the desired microstructure. Due to the domain sizes of ~100nm there is no closed path for exciton dissociation. In addition to that, the sample shows a quite high roughness. Acknowledgement: Authors thank A. G. Cid for SEM images. This work was supported by the German Science Council Center of Advancing Electronics Dresden (cfaed). TEM-EDX results were achieved by funding (support code 03SF0451) through the Helmholtz Energy Materials Characterization Platform (HEMCP) initiated by the Helmholtz Association and the German Federal Ministry of Education and Research (BMBF). References:  S. Pfuetzner, C. Mickel, J. Jankowski, M. Hein, J. Meiss, C. Schuenemann, C. Elschner, A.A. Levin, B. Rellinghaus, K. Leo and M. Riede, “The influence of substrate heating on morphology and layer growth in C60:ZnPc bulk heterojunction solar cells” Org. Electron., 12 (2010), pp. 435–441  A. G. Cid, M. Sedighi, M. Löffler, W. F. van Dorp and E. Zschech, “Energy-Filtered Backscattered Imaging Using Low-Voltage Scanning Electron Microscopy: Characterizing Blends of C60:ZnPc for Organic Solar Cells”. (DOI: 10.1002/adem.201600063)
Authors : Vincent M. Le Corre, Azadeh Rahimi Chatri, L. Jan Anton Koster
Affiliations : Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands
Resume : Following the debate in the literature, we have investigated the importance of the dispersion of charge carrier motion (mobility) on device performance of organic solar cells. Recently, it has been suggested that steady-state mobilities do not reflect the extraction rates of charge carriers (see A. Melianas, Adv. Funct. Mater., 2014, 24, 4507-4514). Pulsed light experiment have shown a net dispersion of the extraction time, which charge carriers losing energy as they move to the electrodes. This would make mobility a time-dependent quantity. Recently, our group has shown that a clear correlation exists between steady-state quantities, such as mobility, and solar cell performance (see D. Bartesaghi, Nat. Comm., 6:7083) This begs the question whether charge carrier extraction can be described with steady-state mobilities. In this contribution, we demonstrate that the extraction of charge carriers from a solar cell is given by a unique steady-state mobility. We have set up a new experiment to measure the charge extraction time from a solar cell in steady-state. To do so we measure the current decay due to a small decrease in light intensity (close to 1 Sun). The lifetime (τ) extracted from the exponential decay, under well-defined conditions, can be related to the mobility (µ) by τ=8Vtµ/L2 (Eq. 1) where Vt is the thermal voltage and L is the device thickness. This new experiment has been applied to different polymer/fullerene blends. The so-obtained mobilities are very close to the values obtained by space-charge-limited mobility measurements. This proves that charge carrier extraction can be described by steady-state quantities.
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Organic solar cells IV : Johan BIJLEVELD
Authors : Nutifafa Y. Doumon* (1), Ryan C. Chiechi (1,2), L. Jan Anton Koster (1)
Affiliations : (1) Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, NL-9747 AG, Groningen-The Netherlands (2) Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, NL-9747 AG, Groningen-The Netherlands
Resume : Novel design of polymers has brought more attention to bulk heterojunction polymer:fullerene solar cells (PSCs) in the past ten years. A typical example is the synthesis, through chemical structure engineering, of the benzodithiophene-co-thieno[3,4-b]thiophene (BDT-TT) backbone based polymers leading to power conversion efficiency (PCE) of over 10%. In this work, we study both device PCE and stability for a set of PBDT-TT – based polymers (the class of PTB7 and its derivative polymers) and the effect of an additive on the solar cell performances. Our results show an enhancement in efficiency (0-84 % rise in PCE) for devices processed with additive. We also observed an accelerated UV-degradation for the same devices. For example, in the case of PTB7, for devices without additive there was ~24 % loss in PCE over 2 hours light exposure. Over the same period, we recorded ~44 % loss for the devices with an additive. Additionally, we conducted a systematic study of UV-degradation of these solar cells. We found that based on the polymer chemical structure, PSCs of polymers with alkoxy side chains are more stable (~25 % loss in PCE) than those with alkylthienyl side chains (~40% loss in PCE). These findings pave the way for new materials that yield efficient as well as stable organic solar cells.
Authors : Dimitar Kutsarov, Edward New, Francesco Bausi, Fernando Castro, S. Ravi P. Silva
Affiliations : Advanced Technology Institute, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford, Surrey, GU2 7XH, UK; Advanced Technology Institute, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford, Surrey, GU2 7XH, UK; National Physical Laboratory, Teddington, Middlesex, TW110LW, UK; National Physical Laboratory, Teddington, Middlesex, TW110LW, UK; Advanced Technology Institute, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford, Surrey, GU2 7XH, UK
Resume : The production of large area organic solar cells (OSCs) in the lab is becoming ever more important to allow the device properties to be analysed on a size scale relevant for future mass production. This requires inexpensive fabrication methodologies in a lab environment using simple coating equipment, to avoid the high investment and running cost of production scale coaters. We demonstrate how a cheap printing proofer can be converted into a sheet-to-sheet slot die coater, with the addition of a slot die head and syringe pump, to allow for production of OSC modules in ambient atmosphere. This coater is shown to produce homogeneous layers of each component of an OSC, where the thickness and morphology of the layers can be controlled by the head speed and temperature of the coating bed. Using a bulk heterojunction system of a Poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT):PC70BM we produce air processed, series connected OSC modules with an efficiency of 4 % on an area of 40 cm2. The modules show a linear increase in open circuit voltage with the connection of the single device stripes, up to 4.4 V for six connected devices. The reproducibility of the stripe coating is confirmed by light beam induced current mapping, showing the small variation in photocurrent across the module and to outline any defects within the device. This is also confirmed by the current-voltage characterisation of each stripe of the module. Our results show how this simple coating process can be used to up-scale the device production in a lab environment for more realistic determination of the real world performance of OSC material systems
Perovskites solar cells V : Itaru OSAKA
Authors : Eline M. Hutter ,Tom J. Savenije
Affiliations : Delft University of Technology, Van der Maasweg 9, 2628 HZ Delft , The Netherlands
Resume : The demand for understanding the photophysical processes in perovskite solar cells has become more evident in view of the rapid rise in device efficiency. The lifetime and mobility of light induced-carriers in photoactive layers are about the most important parameters governing the efficiency of a solar cell. However, there is limited knowledge about the relationship between e.g. preparation route, morphology and precursors and these photo-physical properties. Information on these parameters is obtained by complementary microwave photo-conductance (TRMC) and photo luminescence (PL) measurements. We developed a kinetic model to describe both TRMC and PL experiments with one set of global kinetic parameters. In this kinetic model a short laser pulse leads to photoexcitation of electrons to the conduction band, from where they can recombine with holes in the VB (K2). In competition with second order recombination, electrons can be immobilized in intra-band gap trap states with total density NT. Finally, in case of a non-intrinsic semiconductor, there are additional holes (p0, for p-type) on top of the photo-generated holes. Solving the coupled differential equations yield the time dependent concentrations of holes (np), electrons (ne) and trapped electrons (nt) from which the TRMC and PL traces can be calculated. We could successfully describe the dynamics of different systems including planar and mesoprous layers of MAPI1 and of MAPI single crystals2 using this kinetic model. From the found rate constants and mobilities the corresponding diffusion lengths for minority and majority carriers were deduced. In addition a relation could be made between the synthetic route and po and NT. Interesting findings include: i) The trap density in polycrystalline films is three orders of magnitude higher than in single crystals. ii) The minority carrier diffusion length in MAPI perovskites could exceed 10 μm if it is not limited by the crystal domain size. More recently we extended these studies by introducing a specific electron or hole transport layer allowing us to derive the charge injection rates.3 In short, our methodology gives apart from fundamental insight into the dynamics in perovskites a versatile way to optimize the electronic properties of photoactive layers and their charge transport layers. References 1Hutter, E. M.; Eperon, G. E.; Stranks, S. D.; Savenije, T. J. Charge Carriers in Planar and Meso-Structured Organic-Inorganic Perovskites: Mobilities, Lifetimes, and Concentrations of Trap States. JPCL 2015, 6, 3082-3090. 2Bi, Y.; Hutter, E. M.; Fang, Y.; Dong, Q.; Huang, J.; Savenije, T. J. Charge Carrier Lifetimes Exceeding 15 Μs in Methylammonium Lead Iodide Single Crystals. JPCL 2016, 923-928. 3Ponseca, C. S.; Hutter, E. M.; Piatkowski, P.; Cohen, B.; Pascher, T.; Douhal, A.; Yartsev, A.; Sundström, V.; Savenije, T. J. Mechanism of Charge Transfer and Recombination Dynamics in Organo Metal Halide Perovskites and Organic Electrodes, Pcbm, and Spiro-Ometad: Role of Dark Carriers. J. Am. Chem. Soc. 2015, 137, 16043-16048.
Authors : Sebastian Pont(1), Chieh-Ting Lin(1), Nicholas Aristidou(1), Daniel Bryant(1,2), James Durrant(1,2). Saif Haque(1),
Affiliations : (1) Department of Chemistry, Imperial College London, London, SW7 2AZ, UK (2) SPECIFIC, College of Engineering, Swansea University, Baglan Bay Innovation and Knowledge Centre, Central Avenue, Baglan, United Kingdom, SA12 7AX
Resume : The tunability of the ABX perovskite structure using mixed ions has been key to achieving high photovoltaic efficiencies, for example FA1−xMaxPb(I1−yBry)3. The mixed cation, mixed halide structure enables optimization of the optical band gap of the material whilst maintaining impressive optoelectrical properties. However the effect of mixed ion perovskites structures on the stability has not been critically examined. Here we have investigated the degradation of methyl ammonium lead iodide/bromide (MAPIxBrx-3, x = 0…3) under controlled environmental conditions. For MAPI, the two principal extrinsic degradation mechanisms that have been identified thus far involve sensitivity to humidity and exposure to light + oxygen. The degradation pathway by water vapor was investigated by monitoring films of varying I/Br ratio in an inert atmosphere with controlled humidity. Likewise, the light + oxygen degradation pathway was investigated in dry air and 1 sun equivalent conditions. Using image analysis and XRD we show higher bromine concentration can improve the stability of MAPIxBrx-3 under humid conditions, but a more complex effect is seen under light + oxygen. Compared to MAPI, MAPBr shows much improved material stability in light and oxygen but all mixed films start degrading at the same time. Superoxide analysis and morphological studies show no significance difference between MAPI and MAPBr, suggesting the increased intrinsic crystal stability of MAPBr is the reason for the improved stability seen. Remarkably, the factor limiting the stability of unencapsulated MAPBr solar cell devices is shown to be the organic charge extraction layer and not the perovskite material. Development of stable interlayers can enable fully stable perovskite solar cells.
Authors : Jincheol Kim, Jae S. Yun, Xiaoming Wen, Arman Mahboubi Soufiani, Cho Fai Jonathan Lau, Benjamin Wilkinson, Jan Seidel, Martin A. Green, Shujuan Huang, and Anita W. Y. Ho-Baillie*
Affiliations : The Australian Centre for Advanced Photovoltaics (ACAP), School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, Sydney, 2052, Australia.
Resume : In this work, we have demonstrated a reliable fabrication technique for HC(NH2)2PbI3 planar perovskite solar cells. This is done by controlling the nucleation and crystallization processes of the perovskite layer through a combination of adding HI additive  in the perovskite precursor and gas-assisted  spin coating of the precursor. An average power conversion efficiency (PCE) of 13% can be achieved with negligible hysteresis when measured at a scanning rate of 0.1V/s. The best performing device has a PCE of 16.0%. The narrow spread of PCE’s is due to consistent formation of dense, uniform, pinhole-free good crystalline HC(NH2)2PbI3 film without lead iodide impurities. The effect of process conditions on film growth, physical and electrical proertpies including charge extraction has been comprehensively characterized by scanning electron microscopy, x-ray diffraction, Kelvin probe force microscopy, photoluminescence, and electroluminescence. This is also the first time a combination of nitrogen purge and the addition of HI additive is used in the solution process of HC(NH2)2PbI3 film planar solar cells.  Huang, F. et al. Nano Energy (2014), 10, 10-18.  Eperon, G. E., et al. Energ Environ Sci (2014), 7 (3), 982-988.
Authors : Xiaxia Liao, Severin N. Habisreutinger, Sven Wiesner, Golnaz Sadoughi, Daniel Abou-Ras, Marc A. Gluba, Regan G. Wilks, Roberto Félix, Marin Rusu, Henry J. Snaith, and Marcus Bär Xiaxia Liao1, Severin N. Habisreutinger3, Sven Wiesner1, Golnaz Sadoughi3, Daniel Abou-Ras1, Marc A. Gluba4, Regan G. Wilks1,2, Roberto Félix1, Marin Rusu1, Henry J. Snaith3, and Marcus Bär1,2,5
Affiliations : 1Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, D-14109 Berlin, Germany; 2Energy Materials In-Situ Laboratory Berlin (EMIL), Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Straße 15, 12489 Berlin, Germany; 3Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, OX1 3PU, UK; 4Institute Silicon Photovoltaics, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, D-14109 Berlin, Germany; 5Institut für Physik und Chemie, Brandenburgische Technische Universität Cottbus- Senftenberg, Platz der Deutschen Einheit 1, D-03046 Cottbus, Germany.
Resume : Recent advances in inorganic-organic hybrid perovskite photovoltaic devices represent revolutionary steps in the exploitation of solar energy. However, the stability of perovskite based solar cells is one of the great challenges for the commercialization of this PV technology1,2. In addition to the degradation of the perovskite material under ambient conditions3, the standard hole transport material (HTM) Spiro-OMeTAD has additional issues (e.g., high cost and low conductivity) 4. In organic solar cells, the use of MoO3 as a HTM can considerably enhance the stability of the device5. MoO3 has been used as HTM in perovskite solar cells before, but did not yield high-efficiency devices6. In this contribution, we report a systematic study of the MoO3/CH3NH3PbI3-xClx interface using synchrotron-based hard x-ray photoelectron spectroscopy, scanning electron microscopy, as well as energy-dispersive x-ray, and Raman spectroscopy. A thorough understanding of the chemical and electronic structure of the MoO3/CH3NH3PbI3-xClx interface is crucial for understanding the underlying cause of the performance limitations of related solar cells. We find that the MoO3 (Mo6+) is significantly reduced in the proximity of the interface, and that the formation of Mo5+ induces defect states in the band gap. At the same time, the perovskite decomposes, resulting in PbI2 diffusing through and accumulating at the molybdenum oxide surface. All of these findings indicate that the MoO3/CH3NH3PbI3-xClx interface is inherently unstable, which provides an explanation for the lower than expected power-conversion efficiencies of corresponding devices7. In our contribution, we will discuss the underlying mechanism for the (decomposition) processes and suggest a clear path for avoiding these effects. References  M.A. Green, A. Ho-Baillie and H.J. Snaith. Nature Photonics, 8,506 (2014).  S.T. Williams, A. Rajagopal, C.C. Chueh and a. K.-Y. Jen. J. Phys. Chem. Lett., 7, 811 (2016).  Y. Rong, L. Liu, A. Mei, X. Li and H. Han. Adv. Energy Mater., 5, 1501066, (2015).  G. Sfyri, C. V. Kumar, G. Sabapathi, L. Giribabu, K.S. Andrikopoulos, E. Stathatos and P. Lianos. RSC Adv., 5, 69813 (2015).  X. Hu, L. Chen and Y. Chen. J. Phys. Chem. C, 118, 9930 (2014).  Y. Zhao, A.M. Nardes and K. Zhu. Appl. Phys. Lett., 104, 213906 (2014).  Q.K. Wang, R.B. Wang, P.F. Shen, C. Li, Y.Q. Li, L.J. Liu, S. Duhm, and J.X. Tang. Adv. Mater. Interfaces, 2, 1400528 (2015).
Authors : Małgorzata Wierzbowska, Juan J. Meléndez, Daniele Varsano
Affiliations : Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, PL-02-668, Warsaw, Poland; Department of Physics and Institute for Advanced Scientific Computing of Extremadura (ICCAEX), University of Extremadura, Avenida de Elvas, s/n, 06006, Badajoz, Spain; Center C3, CNR Institute of Nanoscience, Via Campi 231/A, 41100 Modena, Italy
Resume : The energy gap of insulators and semiconductors can change with pressure and temperature, and can be corrected with the energy of the lowest vibrational level, but is expected to be constant in time. Contrarily to this belief, we have found that the band gap in the CH3NH3PbI3 perovskite varies widely, between 0.42 eV and 2.33 eV, depending on the relative arrangement of the freely rotating methylammonium (CH3NH3) molecules in the PbI3 cubic lattice. Since the efficiency of the solar cells in the photovoltaic process depends on the absorption window, these results have very consequences for practical applications. Indeed, CH3NH3PbI3 is a light absorber for low-cost solar cells. Its dynamical gap means that a large window of the Sun spectrum may effectively enter the photovoltaic process, which points to the design of highly efficient cells made upon this compound.
Authors : Ma?gorzata Wierzbowska, Juan J. Meléndez,
Affiliations : Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, PL-02-668, Warsaw, Poland; Department of Physics and Institute for Advanced Scientific Computing of Extremadura (ICCAEX), University of Extremadura, Avenida de Elvas, s/n, 06006, Badajoz, Spain; Center C3, CNR Institute of Nanoscience, Via Campi 231/A, 41100 Modena, Italy
Resume : CH3NH3PbI3 crystal is built of a perovskite-like PbI3 cubic frame and methylammonium (CH3NH3) molecules occupying the central position in the cell. It is commonly believed that the MA molecules are cations, with net charge +1e. On the basis of ab initio calculations, we show that MA in CH3NH3PbI3 behaves instead as an anion with charge -3e. Three electrons transferred to MA from the PbI3 frame originate from the Pb atom (about 1e) and three I atoms (about 2e in total), and locate around C (0.5e), N (0.5e) and H (0.4-0.3e), with respect to the valences of the neutral atoms. As a result of this charge transfer, bands reordering occurs in the MA sublattice with respect to the band structure of the periodic lattice of MA molecules. The reordering is accompanied by a change of the bands character in the PbI3 sublattice with respect to those in the PbI3 frame. Half of the additional charge gained by MA and transferred from the PbI3 frame originates from bands in the energy region [-4.0, 0.0] eV and the rest of charge from deeper states around [-12.0, -11.0] eV.
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