Downloaded from orbit.dtu.dk on: Dec 20, 2017 Upscaling of Indium Tin Oxide (ITO)-Free Polymer Solar Cells Performance, Scalability, Stability, and Flexibility Angmo, Dechan; Krebs, Frederik C Publication date: 2014 Document Version Publisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Angmo, D., & Krebs, F. C. (2014). Upscaling of Indium Tin Oxide (ITO)-Free Polymer Solar Cells: Performance, Scalability, Stability, and Flexibility. Department of Energy Conversion and Storage, Technical University of Denmark. General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Upscaling of Indium Tin Oxide (ITO)- Free Polymer Solar Cells Performance, Scalability, Stability, and Flexibility Ph.D. Dissertation Dechan Angmo September 2013 Upscaling of Indium Tin Oxide (ITO)-Free Polymer Solar Cells Performance, Scalability, Stability, and Flexibility September, 2013 By Dechan Angmo Sponsorship: The project was financed by European Commission as part of Framework 7 ICT 2009 collaborative project HIFLEX (Grant no. 248678) and ROTROT (grant no. 288565) Academic advisor: Professor Frederik C. Krebs Functional Organic Materials, Department of Energy Conversion and Storage Copyright: Reproduction of this publication in whole or in part must include the cus- tomary bibliographic citation, including author attribution, report title, etc. Cover photo: ITO-free highly flexible module, Slot-die coating of photoactive polymer, Roll-to-roll processed modules, Illustration of a typical layer stack , and Current-voltage curves of ITO-free (IOne) modules of different sizes up-to 186 cm2. Published by: Department of Energy Conversion and Storage, Frederiksborgvej 399, Building 775, 4000 Roskilde, Denmark ISBN: 978-87-92986-07-8 Preface Roskilde, September 2013 Sometimes life takes you on a journey only to prepare you for what you wished for. I have always wanted to combine my love and aptitude for science to do something meaningful to the underprivileged part of the world, having grown up in one. Second year in college, I knew I wanted to study renewable energy. Ever since then, I had carved my way to lead me to solar cells. And today, I hand in my thesis with much pride. It would not have been possible without my supervisor, Professor Frederik C. Krebs. I am indebted to him for giving me this opportunity and also for his tireless sup- port throughout the last three years. His commitment and passion to his work is very contagious and has kept me motivated throughout all these years. Dr. Mikkel Jørgen- sen is also specially thanked for always being there when I struggled with scientific problems or with the LBIC instrument. This Ph.D. has been a part of European Commission funded FP7 collaborative project titled HIFLEX. I would like to acknowledge all the people I met under HIFLEX from whom I learnt a lot. Especially, I would like to thank Dr. Yulia Galagan and Dr. Ronn Andreissen for making my research stay at Holst Center in Eindhoven, Nether- lands, a productive and a memorable one. I also extend my gratitude to all my dear colleagues who have never turned a deaf ear to my incessant questions. The camaraderie of this group is unparalleled to any other groups that I have previously worked with. Particularly, I thank Markus Hösel for reading my dissertation and more importantly for catapulting me to my current il- lustrator skills and being my walking-talking Wikipedia on industrial processing. He is always willing to listen to my questions and musings, no matter how trivial. Suren Ge- vorgyan, Henrik Friis Dam, Morten V. Madsen, Thue T. Larsen-Olsen, and Thomas R. i Anderson are especially thanked for listening to my scientific problems and sharing their knowledge without any hesitation. Nieves Espinosa is also thanked for fruitful comments on Chapter 8. I thank Birgitta Andreasen, my only female counterpart in our group for more than 2 years, for being a friend in this far away land. Thanks for lis- tening to me in hard times and sharing laughter in good times. I thank my family for their pride in me and supporting me in whatever I do, wherever I go, and whoever I become. Their love remains unconditional. Finally but most importantly, I thank my late mother. Her 3 o’clock tea in the morning when I used to pull an all-nighter during school was inexpressibly missed this time around. Words have always fallen short when I talk of my mother. Having very lit- tle education herself and coming of very remote region of the world, she has instilled in me the value of education and the need of perseverance and perspiration required to attain it. I am her sacrifices. To her, I dedicate this thesis with a note: my best is yet to come. ii Abstract Polymer solar cells (PSCs) aim to produce clean energy that is cost-competitive to en- ergy produced by fossil fuel-based conventional energy sources. From an environmen- tal perspective, PSCs already compares favorably to other solar cell technologies in terms of fewer emissions of greenhouse gases during production. The cost- competitiveness of PSCs is envisioned achievable by the use of inexpensive materials and high throughput roll-to-roll (R2R) printing and coating techniques. The state-of- the-art of the laboratory PSCs is, however, far removed from the vision of the widely disseminated low-cost solar cells as the laboratory solar cells are mostly focused on in- creasing the power conversion efficiency through materials design with little emphasis on the choice of materials, operational stability and large-scale processing. Indium-tin- oxide (ITO), the commonly used transparent conductor, represents majority of the share of cost and energy footprint in terms of materials and processing in a conven- tional PSC module. Furthermore, the scarcity of indium is feared to create bottleneck in the dawning PSC industry and its brittle nature is an obstacle for fast processing of PSCs on flexible substrates as well as for applications in flexible end products. Thus, the replacement of ITO with low-cost alternatives is crucial for the commercial feasibility of PSCs. Encompassing these concerns, my PhD study has contributed to the development and evaluation of alternatives to ITO in laboratory cells, upscaling of ITO-free concepts from laboratory cells to R2R produced large-area modules, and integration of these module in demonstrator consumer applications. Accordingly, this dissertation is orga- nized into nine chapters. Chapter 1 is aimed at contextualizing PSCs on the world ener- gy map. It aims to address the question: why should PSCs be pursued? Chapter 2 at- tempts to provide a concise yet encompassing introduction to PSCs; and the problem with ITO and possible solutions. It also lays out specific targets that were set before the beginning of PhD study which provides a frame-of-reference for the later chapters. A holistic evaluation of several ITO-free concepts was carried out to determine low-cost upscaling compatibility of these concepts (Chapter 3). The results highlighted three ar- iii chitectures that represented different competencies with regards to photovoltaic per- formance, stability, and low-cost processing. These three architectures were upscaled (Chapter 5-7) using R2R techniques described in detail in Chapter 4. One of the three upscaled architecture (Chapter 7) represented an efficient alternative to ITO in terms of photovoltaic performance and were further investigated for stability and flexibility. These modules were then integrated in a credit-card size laser pointer for demonstra- tion purposes. A colleague, Nieves Espinosa, has conducted life-cycle analyses (LCA) on all the three upscaled ITO-free architectures. Drawing upon the data from her pub- lished work, Chapter 8 provides concise and comparative LCA of the three upscaled ITO-free architectures in order to determine which technology can be pursued further among the three architectures. LCA results of the ITO-free architectures are also com- pared against ITO-based upscaled PSCs as well as against other photovoltaic technolo- gies. Finally, the last chapter (Chapter 9) puts everything in the nutshell and identifies future challenges. iv Resumé Plastsolceller (PSC) har til formål at producere ren energi, der er prismæssigt konkurren- cedygtig sammenlignet med energi produceret af konventionelle fossile brændsler. Fra et miljømæssigt perspektiv sammenlignes PSC allerede positivt til andre solcelle-teknologier i form af færre emissioner af drivhusgasser under produktionen. Konkurrenceevnen for prisen på PSC opnås ved brug af billige materialer og høj hastigheds rulle-til-rulle (R2R) trykning samt coating teknikker. De bedste PSC produceret i laboratorieforhold er langt fra visionen om den meget udbredte billige solcelle, da disse mest er fokuseret på at øget effektiviteten gennem design med lille vægt på valget af materialer, driftsstabilitet og om- fattende behandling. Indium-tin-oxid (ITO), den mest almindeligt anvendte transparente leder, repræsenterer størstedelen af omkostningerne og energi fodaftrykket i form af ma- terialer og forarbejdning i et konventionelt PSC modul. Desuden vil manglen på indium skabe en flaskehals i PSC industrien og samtidig er ITOs struktur en hindring for hurtig be- handling af PSC på fleksible substrater, samt for fleksibiliteten af slutproduktet. Udskift- ning af ITO med billige alternativer er således afgørende for den kommercielle succes for PSC.