Polymerizing M‐Series Acceptors for Efficient Polymer Solar Cells: Effect of the Molecular Shape

Abstract Currently, high‐performance polymerized small‐molecule acceptors (PSMAs) based on ADA‐type SMAs are still rare and greatly demanded for polymer solar cells (PSCs). Herein, two novel regioregular PSMAs (PW‐Se and PS‐Se) are designed and synthesized by using centrosymmetric (linear‐shaped) and axisymmetric (banana‐shaped) ADA‐type SMAs as the main building blocks, respectively. It is demonstrated that photovoltaic performance of the PSMAs can be significantly improved by optimizing the configuration of ADA‐type SMAs. Compared to the axisymmetric SMA‐based polymer (PS‐Se), PW‐Se using a centrosymmetric SMA as the main building block exhibits better backbone coplanarity thereby resulting in bathochromically shifted absorption with a higher absorption coefficient, tighter interchain π–π stacking, and more favorable blend film morphology. As a result, enhanced and more‐balanced charge transport, better exciton dissociation, and reduced charge recombination are achieved for PW‐Se‐based devices with PM6 as polymer donor. Benefiting from these positive factors, the optimal PM6:PW‐Se‐based device exhibits a higher power conversion efficiency (PCE) of 15.65% compared to the PM6:PS‐Se‐based device (8.90%). Furthermore, incorporation of PW‐Se as a third component in the binary active layer of PM6:M36 yields ternary devices with an outstanding PCE of 18.0%, which is the highest value for PSCs based on ADA‐type SMAs, to the best of the knowledge.