4.7 Article

Altering alkyl-chains branching positions for boosting the performance of small-molecule acceptors for highly efficient nonfullerene organic solar cells

Journal

SCIENCE CHINA-CHEMISTRY
Volume 63, Issue 3, Pages 361-369

Publisher

SCIENCE PRESS
DOI: 10.1007/s11426-019-9670-2

Keywords

alkyl-chain branching position; small molecular acceptor; organic solar cell; power conversion efficiency; fill factor

Funding

  1. National Natural Science Foundation of China [21572171, 21702154, 51773157, 51873160]
  2. National Basic Research Program of China [2013CB834805]
  3. Shenzhen Peacock Plan [KQTD2017033011-0107046]
  4. Beijing National Laboratory for Molecular Sciences [BNLMS201905]

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The emergence of the latest generation of small-molecule acceptor (SMA) materials, with Y6 as a typical example, accounts for the surge in device performance for organic solar cells (OSCs). This study proposes two new acceptors named Y6-C2 and Y6-C3, from judicious alteration of alkyl-chains branching positions away from the Y6 backbone. Compared to the Y6, the Y6-C2 exhibits similar optical and electrochemical properties, but better molecular packing and enhanced crystallinity. In contrast, the Y6-C3 shows a significant blue-shift absorption in the solid state relative to the Y6 and Y6-C2. The as-cast PM6:Y6-C2-based OSC yields a higher power conversion efficiency (PCE) of 15.89% than those based on the Y6 (15.24%) and Y6-C3 (13.76%), representing the highest known value for as-cast nonfullerene OSCs. Prominently, the Y6-C2 displays a good compatibility with the PC71BM. Therefore, a ternary OSC device based on PM6:Y6-C2:PC71BM (1.0:1.0:0.2) was produced, and it exhibits an outstanding PCE of 17.06% and an impressive fill factor (FF) of 0.772. Our results improve understanding of the structure-property relationship for state-of-the-art SMAs and demonstrate that modulating the structure of SMAs via fine-tuning of alkyl-chains branching positions is an effective method to enhance their performance.

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