Journal
CHEMISTRY OF MATERIALS
Volume 22, Issue 5, Pages 1673-1679Publisher
AMER CHEMICAL SOC
DOI: 10.1021/cm903067a
Keywords
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Funding
- U S. Department of Energy [DE-AC02-05CH11231]
- Center for Advanced Molecular Photovoltaics [KUS-CI-015-21]
- King Abdullah University of Science and Technology (KAUST)
- National Science Foundation
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The solar cell performance of poly[3-(4-n-octyl)-phenylthiophene] (POPT) and poly(3-hexylthiophene) (P3HT) are compared in devices using 4,7-bis(2-(1-(2-ethylhexyl)-4,5-dicyanomidazol-2-yl)vinyl)benzo[c][1,2,5]-thiadiazole (EV-BT) as the electron acceptor. Despite their reduced light absorption, POPT EV-BT devices generate higher photocurrents in both bilayer and bulk heterojunction (BHJ) architectures than analogous P3HT.EV-BT devices. Optimized POPT EV-BT BHJ devices achieve 1 4% average efficiency, whereas the analogous P3HT devices only reach 1.1% Morphology does not account for the large difference in performance as AFM studies of the active layer suggest comparable levels of phase separation in the two systems Reverse bias analysis demonstrates that P3HT devices have a higher maximum potential than POPT devices, but P3HT devices appear to be more Severely limited by recombination losses under standard operating conditions. A possible explanation for the superior performance in POPT devices is that the pendant phenyl ring in POPT can twist out-of-plane and Increase the Separation distance with the acceptor molecule A larger donor/acceptor separation distance can destabilize the geminate pair and lead to more efficient charge separation in POPT.EV-BT devices. Our results emphasize the importance of donor/acceptor pair interactions and its effect on charge separation processes in polymer solar cells.
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