Non-Fullerene Acceptor Doped Block Copolymer for Efficient and Stable Organic Solar Cells

Bulk-heterojunction organic solar cells (OSCs) often suffer from morphological instability due to thermo- or photoinduced molecular diffusion. To circumvent such instability, OSCs incorporating a single-component block copolymer with covalently bonded blocks can restrain molecular diffusion. However, the device efficiencies of such block copolymers are lagging behind those based on a blended active layer due to a nonideal morphological problem. Herein, we successfully alleviate this problem by introducing a small-molecule additive, Y6, having a structure similar to that of the acceptor block. The addition of Y6 improves the packing of acceptor blocks in the block copolymer, PM6-b-PYIT. This helps improve electron transport and enhances the device efficiency to 15.55%, representing the highest value reported for block-copolymer-based OSCs. Moreover, the device stability is significantly improved due to the padding of Y6 into the nanovoids of the copolymer matrix to restrict the molecular motion. This work presents an effective strategy to address the efficiency-stability tradeoff in OSCs.