Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 7, Issue 48, Pages 26999-27005Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.5b09497
Keywords
organic solar cells; organic photovoltaics; charge transfer states; carrier recombination; energetic disorder
Funding
- Office of Naval Research (ONR) [N000141110245]
- National Science Foundation [CHE-115164]
- Direct For Mathematical & Physical Scien
- Division Of Chemistry [1504727] Funding Source: National Science Foundation
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The effect of polymer side chains on device performance was investigated for PBDT(EtHex)-TPD-(Oct):PC70BM and PBDT (EtHex)-TPD (EtHex) :PC70BM BHJ solar cells. Going from a linear side chain on the polymer's acceptor moiety to a branched side chain was determined to have a negative impact on the overall device efficiency, because of significantly reduced short-circuit current (J(sc)) and fill factor (FF) values. Sub-bandgap external quantum efficiency (EQE) and transient photoluminescence (PL) measurements showed more-efficient carrier generation for the polymer with linear side chains, because of a higher degree of charge-transfer (CT) state delocalization, leading to more-efficient exciton dissociation. Furthermore, the increase in pi-pi stacking distance and disorder for the bulkier ethylhexyl side chain were shown to result in a lower hole mobility, a higher bimolecular recombination, and a higher energetic disorder. The use of linear side chains on the polymer's acceptor moiety was shown to promote photogeneration, because of more-effective CT states and favorable carrier transport resulting in improved solar cell performance.
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