A polymer acceptor with grafted small molecule acceptor units for high-efficiency organic solar cells

Polymerization of small molecule acceptors (SMAs) has been proved to be an effective strategy to design polymer acceptors, in which the polymerization reaction is conducted via the coupling between the end groups of SMAs and linkers. However, polymer acceptors synthesized in this polymerization way cannot remain the favored packing modes of end groups in the original SMAs. Herein, we propose a strategy for designing polymer acceptors with grafted SMA units via the polymerization between central building blocks of SMAs and linkers. Polymer acceptors designed using this strategy can not only free the end groups to facilitate effective packing similar to SMAs but also form extended conjugation and double charge transport channels. With this strategy, a polymer acceptor SH-1 was synthesized, which shows more compact and ordered intermolecular packing in both neat and blended films compared with the corresponding SH-2 synthesized by conventional copolymerization via end groups and linkers. The all-polymer solar cells based on PM6:SH-1 showed a power conversion efficiency (PCE) of 14.14%, substantially higher than that of the PM6:SH-2 based device with an efficiency of 6.55%. This work provides a new strategy for designing polymer acceptors with great potential through further careful regulation of both main building blocks and linker groups.