LAUSR

Abstract We present the first report incorporating strongly electron-donating moiety pyrrolo[3,2-b]pyrrole into fused-ring electron acceptors, and design and synthesize two narrow-bandgap nonfullerene acceptor isomers PPIC1 and PPIC2. These two molecules bear the same electron-withdrawing terminal groups and isomeric eight-fused-ring cores. The two compounds exhibit strong light-harvesting ability in the near-infrared region beyond 1000 nm. Compared with the symmetric PPIC2, the asymmetrical PPIC1 shows remarkably blue-shifted absorption, wider bandgap, down-shifted highest occupied molecular orbital, up-shifted lowest unoccupied molecular orbital, and lower electron mobility. Paired with the classical polymer donor PTB7-Th, PPIC1-based photovoltaic devices exhibit higher open-circuit voltage, short-circuit current and efficiency than the PPIC2-based devices.