Journal
MATERIALS
Volume 6, Issue 3, Pages 897-910Publisher
MDPI
DOI: 10.3390/ma6030897
Keywords
transient spectroscopy; organic photovoltaic; donor-acceptor blends; charge-transfer excitons
Categories
Funding
- DOE at the University of Utah [DE-FG02-04ER46109]
- U.S. Department of Energy (DOE) [DE-FG02-04ER46109] Funding Source: U.S. Department of Energy (DOE)
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We measured the picoseconds (ps) transient dynamics of photoexcitations in blends of regio-regular poly(3-hexyl-thiophene) (RR-P3HT) (donors-D) and fullerene (PCBM) (acceptor-A) in an unprecedented broad spectral range of 0.25 to 2.5 eV. In D-A blends with maximum domain separation, such as RR-P3HT/PCBM, with (1.2:1) weight ratio having solar cell power conversion efficiency of similar to 4%, we found that although the intrachain excitons in the polymer domains decay within similar to 10 ps, no charge polarons are generated at their expense up to similar to 1 ns. Instead, there is a build-up of charge-transfer (CT) excitons at the D-A interfaces having the same kinetics as the exciton decay. The CT excitons dissociate into separate polarons in the D and A domains at a later time (>1 ns). This two-step charge photogeneration process may be typical in organic bulk heterojunction cells. We also report the effect of adding spin 1/2 radicals, Galvinoxyl on the ultrafast photoexcitation dynamics in annealed films of RR-P3HT/PCBM blend. The addition of Galvinoxyl radicals to the blend reduces the geminate recombination rate of photogenerated CT excitons. In addition, the photoexcitation dynamics in a new D-A blend of RR-P3HT/Indene C60 trisadduct (ICTA) has been studied and compared with the dynamics in RR-P3HT/PCBM.
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