Quasi-Homojunction Organic Nonfullerene Photovoltaics Featuring Fundamentals Distinct from Bulk Heterojunctions

Yifan Wang, Michael B. Price, Raja Sekhar Bobba, Heng Lu, Jingwei Xue, Yilin Wang, Mengyang Li, Aleksandra Ilina, Paul A. Hume, Boyu Jia, Tengfei Li, Yuchen Zhang, Nathaniel J.L.K. Davis, Zheng Tang, Wei Ma, Quinn Qiao, Justin M. Hodgkiss, Xiaowei Zhan

Research output: Contribution to journalArticlepeer-review

24 Scopus citations

Abstract

In contrast to classical bulk heterojunction (BHJ) in organic solar cells (OSCs), the quasi-homojunction (QHJ) with extremely low donor content (≤10 wt.%) is unusual and generally yields much lower device efficiency. Here, representative polymer donors and nonfullerene acceptors are selected to fabricate QHJ OSCs, and a complete picture for the operation mechanisms of high-efficiency QHJ devices is illustrated. PTB7-Th:Y6 QHJ devices at donor:acceptor (D:A) ratios of 1:8 or 1:20 can achieve 95% or 64% of the efficiency obtained from its BHJ counterpart at the optimal D:A ratio of 1:1.2, respectively, whereas QHJ devices with other donors or acceptors suffer from rapid roll-off of efficiency when the donors are diluted. Through device physics and photophysics analyses, it is observed that a large portion of free charges can be intrinsically generated in the neat Y6 domains rather than at the D/A interface. Y6 also serves as an ambipolar transport channel, so that hole transport as also mainly through Y6 phase. The key role of PTB7-Th is primarily to reduce charge recombination, likely assisted by enhancing quadrupolar fields within Y6 itself, rather than the previously thought principal roles of light absorption, exciton splitting, and hole transport.

Original languageEnglish (US)
Article number2206717
JournalAdvanced Materials
Volume34
Issue number50
DOIs
StatePublished - Dec 15 2022

Keywords

  • fused-ring electron acceptor
  • nonfullerene
  • organic solar cell
  • quasi-homojunction

ASJC Scopus subject areas

  • General Materials Science
  • Mechanics of Materials
  • Mechanical Engineering

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