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

Singh, Sanjeev; Vardeny, Zeev

doi:10.3390/ma6030897

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

Journal Article · Fri Mar 01 00:00:00 EST 2013 · Materials

DOI:https://doi.org/10.3390/ma6030897· OSTI ID:1628437

Singh, Sanjeev ^[1]; Vardeny, Zeev ^[2]

Univ. of Utah, Salt Lake City, UT (United States). Dept. of Physics and Astronomy; DOE/OSTI
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.

View Accepted Manuscript (DOE)

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, Journal Name: Materials Journal Issue: 3 Vol. 6; ISSN 1996-1944; ISSN MATEG9

Publisher:: MDPICopyright Statement

Country of Publication:: United States

Language:: English

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