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Materials 2013, 6(3), 897-910; doi:10.3390/ma6030897
Article

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

 and *
Department of Physics & Astronomy, University of Utah, Salt Lake City, UT 84112, USA Current address: School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
* Author to whom correspondence should be addressed.
Received: 21 December 2012 / Revised: 4 February 2013 / Accepted: 25 February 2013 / Published: 6 March 2013
(This article belongs to the Special Issue Photovoltaic Materials)
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Abstract

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.
Keywords: transient spectroscopy; organic photovoltaic; donor-acceptor blends; charge-transfer excitons transient spectroscopy; organic photovoltaic; donor-acceptor blends; charge-transfer excitons
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Singh, S.; Vardeny, Z.V. Ultrafast Transient Spectroscopy of Polymer/Fullerene Blends for Organic Photovoltaic Applications. Materials 2013, 6, 897-910.

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