Influence of Fullerene Acceptor on the Performance,Microstructure, and Photophysics of Low Bandgap Polymer Solar Cells |
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Authors: | Wenchao Huang Eliot Gann Naresh Chandrasekaran Shyamal K K Prasad Sheng‐Yung Chang Lars Thomsen Dinesh Kabra Justin M Hodgkiss Yi‐Bing Cheng Yang Yang Christopher R McNeill |
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Institution: | 1. Department of Materials Science and Engineering, Monash University, Clayton, VIC, Australia;2. California NanoSystems Institute, University of California, Los Angeles, CA, USA;3. Department of Materials Science and Engineering, University of California, Los Angeles, CA, USA;4. Australian Synchrotron, Clayton, VIC, Australia;5. Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai, India;6. IITB‐Monash Research Academy, IIT Bombay, Mumbai, India;7. MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington, Wellington, New Zealand |
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Abstract: | The morphology, photophysics, and device performance of solar cells based on the low bandgap polymer poly2,6′‐4,8‐di(5‐ethylhexylthienyl)benzo1,2‐b;3,3‐b]dithiophene]3‐fluoro‐2(2‐ethylhexyl)carbonyl]thieno3,4‐b]thiophenediyl (PBDTTT‐EFT) (also known as PTB7‐Th) blended with different fullerene acceptors: Phenyl‐C61‐butyric acid methyl ester (PC61BM), phenyl‐C71 ‐butyric acid methyl ester (PC71BM), or indene‐C60 bisadduct (ICBA) are correlated. Compared to PC71 BM‐based cells – which achieve a power conversion efficiency (PCE) of 9.4% – cells using ICBA achieve a higher open‐circuit voltage (VOC) of 1.0 V albeit with a lower PCE of 7.1%. To understand the origin of this lower PCE, the morphology and photophysics have been thoroughly characterized. Hard and soft X‐ray scattering measurements reveal that the PBDTTT‐EFT:ICBA blend has a lower crystallinity, lower domain purity, and smaller domain size compared to the PBDTTT‐EFT:PC71BM blend. Incomplete photoluminescence quenching is also found in the ICBA blend with transient absorption measurements showing faster recombination dynamics at short timescales. Transient photovoltage measurements highlight further differences in recombination at longer timeframes due to the more intermixed morphology of the ICBA blend. Interestingly, a mild thermal treatment improves the performance of PBDTTT‐EFT:ICBA cells which is exploited in the fabrication of a homo PBDTTT‐EFT:ICBA tandem solar cell with PCE of 9.0% and VOC of 1.93 V. |
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Keywords: | fullerene derivatives morphology photophysics polymer solar cells tandem solar cells |
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