Journal
CHEMISTRY OF MATERIALS
Volume 26, Issue 14, Pages 4109-4118Publisher
AMER CHEMICAL SOC
DOI: 10.1021/cm5010483
Keywords
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Funding
- Office of Naval Research [N000141410076]
- Max Planck Research Group
- Deutsche Forschungsgemeinschaft (DFG) [SPP1355]
- Fonds der Chemischen Industrie (FCI)
- National Science Foundation Graduate Research Fellowship
- U.S. Department of Energy, Office of Basic Energy Sciences [DE-AC02-76SF00515]
- Dreyfus Teacher Scholar Award
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The photovoltaic performance and charge generation dynamics in thin film bulk heterojunction organic photovoltaic (BHJ OPV) devices comprising the small molecule donor 7,7'-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithiophene-2,6-diyl)bis(6-fluoro-4-(5'-hexyl-[2,2'-bithiophen]-5-yl)benzo[c][1,2,5]thiadiazole) (p-DTS(FBTTh2)(2)) and a perylene diimide (PDI) electron acceptor are investigated with and without the processing additive 1,8-diiodooctane (DIO). UV-vis absorption spectroscopy indicates that the use of DIO during processing increases the structural order of both p-DTS(FBTTh2)(2) and PDI compared to films cast from chlorobenzene alone. Excitation intensity dependent broadband vis-NIR transient absorption pump-probe experiments over a dynamic range from 100 fs to 100 mu s reveal that, in blends processed without DIO, essentially none of the interfacial charge transfer states generated after exciton dissociation at the donor-acceptor interface split into spatially separated charge carriers. In contrast, in blends processed with 0.4 vol% DIO, geminate recombination is significantly reduced, and spatially separated charge carriers are generated. It appears that the drastic increase in the power conversion efficiency in p-DTS(FBTTh2)(2):PDI BHJ OPV devices upon the use of DIO, from 0.13% to 3.1%, is a consequence of the increased solid state order of both p-DTS(FBTTh2)(2) and PDI, which leads to a significant improvement of the exciton dissociation efficiency and makes this system among the most efficient non-fullerene BHJ organic solar cells to date.
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