Journal
ADVANCED ENERGY MATERIALS
Volume 10, Issue 8, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/aenm.201902430
Keywords
charge generation; charge transport; morphology; nonfullerene acceptors; polymer aggregation
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Funding
- Office of Naval Research [N00014-17-1-2243, N00014-17-1-2242]
- NSF [CBET-1639429]
- ONR [N000141712204]
- Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy [DE-AC02-05CH11231]
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Understanding the correlation between polymer aggregation, miscibility, and device performance is important to establish a set of chemistry design rules for donor polymers with nonfullerene acceptors (NFAs). Employing a donor polymer with strong temperature-dependent aggregation, namely PffBT4T-2OD [poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3 '''-di(2-octyldodecyl)-2,2 ';5 ',2 '';5 '',2 '''-quaterthiophen-5,5-diyl)], also known as PCE-11 as a base polymer, five copolymer derivatives having a different thiophene linker composition are blended with the common NFA O-IDTBR to investigate their photovoltaic performance. While the donor polymers have similar optoelectronic properties, it is found that the device power conversion efficiency changes drastically from 1.8% to 8.7% as a function of thiophene content in the donor polymer. Results of structural characterization show that polymer aggregation and miscibility with O-IDTBR are a strong function of the chemical composition, leading to different donor-acceptor blend morphology. Polymers having a strong tendency to aggregate are found to undergo fast aggregation prior to liquid-liquid phase separation and have a higher miscibility with NFA. These properties result in smaller mixed donor-acceptor domains, stronger PL quenching, and more efficient exciton dissociation in the resulting cells. This work indicates the importance of both polymer aggregation and donor-acceptor interaction on the formation of bulk heterojunctions in polymer:NFA blends.
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