Benzodifuran-based polymer donors for binary all-polymer solar cells with nearly 18% efficiency

Owing to the strong intermolecular interactions and high energy levels of benzodifuran (BDF)-based copolymers, their photovoltaic performance has progressed slowly. Herein, a "strong donor–weak acceptor" design strategy is proposed that can effectively optimize the strong intermolecular interactions of BDF-based polymers by using the steric effect of long alkyl side chains to weaken the dithiophene quinoxaline-based acceptor unit. Two new high-performance polymer donors, PQR16-BFCl and PQR16-BFF, were prepared via copolymerization with BDF unit. The binary all-polymer solar cells fabricated by combining PQR16-BFCl and PQR16-BFF with PY-IT achieved power conversion efficiencies of 17.91% and 17.26%, respectively, along with high fill factors exceeding 75%. Notably, PQR16-BFCl:PY-IT set a new record efficiency for BDF-based all-polymer solar cell binary devices. This study showed that the strong interaction advantage of BDF can be utilized in a weak acceptor unit system, showing prominent advantages in stabilizing the orientation of polymer molecules, alleviating steric hindrance, and reducing aggregation. This study demonstrates the application of BDF-based donor units and will undoubtedly accelerate the development of BDF-based polymer solar cells. • Developed a novel high-performance benzofuran-based polymer donor. • “Strong donor & weak acceptor” design strategy is proposed. • A nearly 18% efficiency was obtained, one of the highest values reported so far for benzofuran-based APSCs. • Long alkyl side chains effectively optimize intermolecular interaction.