Relationship between interchain interaction, exciton delocalization, and charge separation in low-bandgap copolymer blends

Zhi Guo, Doyun Lee, Richard Daniel Schaller, Xiaobing Zuo, Byeongdu Lee, Tengfei Luo, Haifeng Gao, Libai Huang*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

78 Scopus citations


We present a systematic study of the roles of crystallinity, interchain interaction, and exciton delocalization on ultrafast charge separation pathways in donor-acceptor copoloymer blends. We characterize the energy levels, excited state structures, and dynamics of the interchain species by combined ultrafast spectroscopy and computational quantum chemistry approaches. The alkyl side chain of a highly efficient donor-acceptor copolymer for solar cell applications, PBDTTT (poly(4,8-bis-alkyloxybenzo[1,2-b:4,5-b']dithiophene-2,6- diyl-alt-(alkylthieno[3,4-b]thiophene-2-carboxylate)-2,6-diyl), is varied to tune the molecular packing and interchain interaction of the polymers in order to elucidate the charge separation pathways originating from intrachain and interchain species. Polymers with linear side chains result in more crystalline polymer domain that lead to preferential formation of interchain excitons delocalizing over more than one polymer backbone in the solid state. Our results demonstrate that the higher polymer crystallinity leads to slower charge separation due to coarser phase segregation and formation of the interchain excited states that are energetically unfavorable for charge separation. Such energetics of the interchain excitons in low-bandgap copolymers calls for optimized solar cell morphologies that are fundamentally different from those based on homopolymers such as P3HT (poly-3-hexylthiophene). A long-range crystalline polymer domain is detrimental rather than beneficial to solar cell performance for a low-bandgap copolymer which is in direct contrast to the observed behavior in P3HT based devices.

Original languageEnglish (US)
Pages (from-to)10024-10032
Number of pages9
JournalJournal of the American Chemical Society
Issue number28
StatePublished - Jul 16 2014

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry


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