Benzo[b][1,4]diazepine: a new electron-deficient unit for high-performance small-molecule acceptors.

Central-core engineering of small-molecule acceptors (SMAs) underpins performance advances in organic solar cells (OSCs), yet the development of new electron-deficient core structures remains limited. Here, we introduce benzo[b][1,4]diazepine as an electron-deficient central unit and construct two acceptors, difluoromethyl-substituted BDA-2F and trifluoromethyl-substituted BDA-3F. Enabled by F-H non-covalent interactions, moderately fluorinated BDA-2F delivers improved molecular packing, and enhanced electron mobility. D18:BDA-2F devices reach a high efficiency of 18.98%, exceeding the 16.52% for BDA-3F.