The influence of microstructure on charge separation dynamics in organic bulk heterojunction materials for solar cell applications

Mariateresa Scarongella, Arun Aby Paraecattil, Ester Buchaca-Domingo, Jessica D. Douglas, Serge Beaupré, Thomas McCarthy-Ward, Martin J. Heeney, Jacques Edouard Moser, Mario Leclerc, Jean Frechet, Natalie Stingelin, Natalie Banerji

Research output: Contribution to journalArticlepeer-review

45 Scopus citations

Abstract

Light-induced charge formation is essential for the generation of photocurrent in organic solar cells. In order to gain a better understanding of this complex process, we have investigated the femtosecond dynamics of charge separation upon selective excitation of either the fullerene or the polymer in different bulk heterojunction blends with well-characterized microstructure. Blends of the pBTTT and PBDTTPD polymers with PCBM gave us access to three different scenarios: either a single intermixed phase, an intermixed phase with additional pure PCBM clusters, or a three-phase microstructure of pure polymer aggregates, pure fullerene clusters and intermixed regions. We found that ultrafast charge separation (by electron or hole transfer) occurs predominantly in intermixed regions, while charges are generated more slowly from excitons in pure domains that require diffusion to a charge generation site. The pure domains are helpful to prevent geminate charge recombination, but they must be sufficiently small not to become exciton traps. By varying the polymer packing, backbone planarity and chain length, we have shown that exciton diffusion out of small polymer aggregates in the highly efficient PBDTTPD:PCBM blend occurs within the same chain and is helped by delocalization. This journal is © the Partner Organisations 2014.
Original languageEnglish (US)
Pages (from-to)6218-6230
Number of pages13
JournalJ. Mater. Chem. A
Volume2
Issue number17
DOIs
StatePublished - 2014

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Materials Science(all)
  • Chemistry(all)

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