Charge pair dissociation and recombination dynamics in a P3HT–PC60BM bulk heterojunction
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The mechanism by which Coulombically bound charge pairs dissociate into free carriers in photovoltaic donor–acceptor blends is of great interest. Here, we use polarization-sensitive transient absorption (TA) to study the diffusion of photogenerated holes in a polythiophene (P3HT)–fullerene (PC60BM) blend. We observe an initial anisotropy value of 0.4 for the absorption of photogenerated holes, indicating that holes generated on a 100 fs time scale are localized on the same polymer chain as their precursor excitons. Depolarization dynamics indicate fast initial hole motion on a 0.3 ps time scale and slower migration up to 100 ps. Charge pair recombination is found to occur on a much longer time scale of 10–1000 ns via a purely bimolecular process independent of excess energy. Our results show that nearly all charge pairs get separated by at least 7 nm in the absence of an external field and indicate that high charge mobility is crucial for charge separation.
Matheson , A B , Pearson , S J , Ruseckas , A & Samuel , I D W 2013 , ' Charge pair dissociation and recombination dynamics in a P3HT–PC 60 BM bulk heterojunction ' Journal of Physical Chemistry Letters , vol 4 , no. 23 , pp. 4166 . DOI: 10.1021/jz4020426
Journal of Physical Chemistry Letters
Copyright © 2013 American Chemical Society. This work is made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://dx.doi.org/10.1021/jz4020426
The authors thank the EPSRC, SUPA, the Condensed Matter Doctoral Training Centre and the European Union Seventh Framework programme (grant agreement 321305) for financial support.
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