Donor Polymer Can Assist Electron Transport in Bulk Heterojunction Blends with Small Energetic Offsets

Hang Yin, Lik Kuen Ma, Yilin Wang, Jiachen Huang, Han Yu, Jianquan Zhang, Philip C.Y. Chow, Wei Ma, Shu Kong SO*, He Yan

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

20 Citations (Scopus)

Abstract

Conventional organic solar cell (OSC) systems have significant energy offsets between the donor and acceptor both at the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels. Because of this, in a bulk heterojunction (BHJ) system, electrons typically transport in acceptors, whereas holes typically transport in donors. It is not favorable for electrons to hop back and forth between the donor and acceptor because the hopping is energetically disfavored. In such conventional OSC systems, the addition of donor polymer to acceptor films should typically reduce the electron mobility. In this study, a surprisingly large increase (up to 30×) in electron mobility is observed in an OSC blend when introducing a polymer donor into small molecular acceptor. By ruling out morphology reasons, it is shown that the donor polymer can assist the electron transport by providing “bridges” or a “shortcut” for electron transport across the domains of small molecular acceptors. This can happen because, for these systems, the LUMO offset is small. The study shows the benefits of donor-assisted electron transport in BHJ systems with small energetic offsets. This finding could be also applied to other fields to tune the optimized charge transport property of organic materials or slush blends.

Original languageEnglish
Article number1903998
JournalAdvanced Materials
Volume31
Issue number44
DOIs
Publication statusPublished - 1 Nov 2019

Scopus Subject Areas

  • Materials Science(all)
  • Mechanics of Materials
  • Mechanical Engineering

User-Defined Keywords

  • electron mobility
  • intrinsic mobility in donors
  • low driving force
  • organic solar cells
  • topology

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