Charge pair dissociation and recombination dynamics in a P3HT–PC60BM bulk heterojunction

Andrew Barclay Matheson, Scott James Pearson, Arvydas Ruseckas, Ifor David William Samuel

Research output: Contribution to journalLetterpeer-review

18 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)4166
Number of pages4171
JournalJournal of Physical Chemistry Letters
Volume4
Issue number23
Early online date18 Nov 2013
DOIs
Publication statusPublished - 5 Dec 2013

Keywords

  • OPV
  • Polaron
  • Separation
  • Depolarization
  • Anisotropy
  • Transient absorption

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