Effect of molecular weight on morphology and photovoltaic properties in P3HT:PCBM solar cells |
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| Affiliation: | 1. Hasselt University, Campus Diepenbeek, Institute for Materials Research (IMO), Materials Physics, Wetenschapspark 1, 3590 Diepenbeek, Belgium;2. Hasselt University, Campus Diepenbeek, Institute for Materials Research (IMO), Design & Synthesis of Organic Semiconductors (DSOS), Agoralaan-Building D, 3590 Diepenbeek, Belgium;3. IMEC, Division IMOMEC, Wetenschapspark 1, 3590 Diepenbeek, Belgium;4. Institut für Angewandte Photophysik, Technische Universität Dresden, George-Bähr-Straße 1, 01069 Dresden, Germany;5. Department of Physical Chemistry and Polymer Science, Faculty of Engineering Sciences, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium;6. Institute of Physics, Carl von Ossietzky University, 26111 Oldenburg, Germany;1. Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, 199 Ren’ai Road, Suzhou 215123, Jiangsu, PR China;2. Shanghai Ultra-precision Optical Manufacturing Engineering Research Center, and Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Optical Science and Engineering, Fudan University, Shanghai 200433, PR China;1. School of Applied Physics, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600, Selangor, Malaysia;2. Solar Energy Research Institute, UniversitiKebangsaan Malaysia, 43600, Bangi, Selangor, Malaysia;3. Advanced Displayed Research Centre, Department of Information Display, Kyung HeeUniversity, Dongdaemoon-gu, Seoul, 130-701, South Korea;1. Departamento de Física, Centro de Ciências Exatas, Universidade Estadual de Londrina, 86051-990 Londrina, PR, Brazil;2. School of Electronic Engineering, Bangor University, Dean St., Bangor, Gwynedd LL57 1UT, Wales, UK;1. Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), 08193 Bellaterra, Spain;2. Department of Applied Physics, Technical University of Cartagena (UPCT), ETSII, 30202, Cartagena, Spain;3. Department of Electronics, Technical University of Cartagena (UPCT), Plaza Hospital 1, 30202 Cartagena, Spain |
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| Abstract: | The molecular weight of poly(3-hexylthiophene) is an important factor influencing the photovoltaic properties of bulk heterojunction organic solar cells based on this material. However, since different synthetic processes or repetitive soxhlet extractions – generally applied to obtain the different molecular weight batches under study – result in samples with simultaneously varying regioregularity (RR) and polydispersity index (PDI), it has not been possible yet to find an unambiguous correlation between the molecular weight and the photovoltaic performance. In the present work preparative gel permeation chromatography is introduced as a versatile technique to fractionate the donor polymer and thereby obtain a systematic variation of the number average molecular weight (Mn = 11–91 kg mol−1) with an almost constant PDI and RR. Polymer crystallinity and conjugation length are evaluated by UV–Vis spectroscopy, rapid heat-cool calorimetry and selected area electron diffraction, and are found to be deeply affected by Mn. This in turn influences the behavior of the charge transfer state energy, measured via Fourier transform photocurrent spectroscopy, and therefore the open-circuit voltage. The short-circuit current is also affected by Mn, but mainly due to a change in absorption coefficient. The apparent recombination order is shown to be linked to the morphology of the polymer:fullerene blend and is determined using transient photovoltage and photocurrent techniques. Finally, a correlation between recombination and fill factor is also suggested. |
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| Keywords: | Molecular weight Crystallinity Preparative gel permeation chromatography Recombination order |
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