Limits for Recombination in a Low Energy Loss Organic Heterojunction

S. Matthew Menke, Aditya Sadhanala, Mark Nikolka, Niva A. Ran, Mahesh Kumar Ravva, Safwat Abdel-Azeim, Hannah L. Stern, Ming Wang, Henning Sirringhaus, Thuc Quyen Nguyen, Jean Luc Brédas, Guillermo C. Bazan, Richard H. Friend

Research output: Contribution to journalArticlepeer-review

78 Scopus citations


Donor-acceptor organic solar cells often show high quantum yields for charge collection, but relatively low open-circuit voltages (VOC) limit power conversion efficiencies to around 12%. We report here the behavior of a system, PIPCP:PC61BM, that exhibits very low electronic disorder (Urbach energy less than 27 meV), very high carrier mobilities in the blend (field-effect mobility for holes >10-2 cm2 V-1 s-1), and a very low driving energy for initial charge separation (50 meV). These characteristics should give excellent performance, and indeed, the VOC is high relative to the donor energy gap. However, we find the overall performance is limited by recombination, with formation of lower-lying triplet excitons on the donor accounting for 90% of the recombination. We find this is a bimolecular process that happens on time scales as short as 100 ps. Thus, although the absence of disorder and the associated high carrier mobility speeds up charge diffusion and extraction at the electrodes, which we measure as early as 1 ns, this also speeds up the recombination channel, giving overall a modest quantum yield of around 60%. We discuss strategies to remove the triplet exciton recombination channel.

Original languageEnglish (US)
Pages (from-to)10736-10744
Number of pages9
JournalACS Nano
Issue number12
StatePublished - Dec 27 2016
Externally publishedYes


  • charge recombination
  • charge transfer states
  • energy loss
  • high mobility
  • organic solar cell

ASJC Scopus subject areas

  • General Materials Science
  • General Engineering
  • General Physics and Astronomy


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