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Title: Ultrafast Transient Spectroscopy of Polymer/Fullerene Blends for Organic Photovoltaic Applications

Journal Article · · Materials
DOI:https://doi.org/10.3390/ma6030897· OSTI ID:1628437
 [1];  [1]
  1. Univ. of Utah, Salt Lake City, UT (United States). Dept. of Physics and Astronomy

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 ~4%, we found that although the intrachain excitons in the polymer domains decay within ~10 ps, no charge polarons are generated at their expense up 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.

Research Organization:
Univ. of Utah, Salt Lake City, UT (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division
Grant/Contract Number:
FG02-04ER46109
OSTI ID:
1628437
Journal Information:
Materials, Vol. 6, Issue 3; ISSN 1996-1944
Publisher:
MDPICopyright Statement
Country of Publication:
United States
Language:
English

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