Trifluoromethylation Enables a 3D Interpenetrated Low-Band-Gap Acceptor for Efficient Organic Solar Cells

The power conversion efficiencies (PCEs) of organic solar cells have broken through 16% at a fast speed based on nonfullerene acceptors (NFAs). However, it is still a great challenge to design and synthesize ultra-narrow band-gap (Eg^opt ≤ 1.3 eV) NFAs to overcome the limited absorption in the near-infrared (NIR) region for further improvement of efficiencies. Herein, trifluoromethylation has proven to be an effective strategy to achieve an ultra-narrow band-gap NFA (named BTIC-CF3-γ). A PCE of 15.59% has been achieved, which is the highest value in reported ultra-narrow band-gap acceptors. Meanwhile, a ternary device with 16.50% efficiency is also realized, resulting from its red-shifted absorptions. More importantly, the single-crystal structure of BTIC-CF3-γ has been successfully presented that gives an insight into the solid-state molecular packings, which will help to understand the charge transportation in blend films and also provide ideas for designing high-performance molecules.
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