Self‐Doped Perylene Diimide‐Based Polymers for Simultaneous Improvements in Efficiency and Thermal Stability of Organic Solar Cells

Research on electron transporting layers (ETLs) for organic solar cells (OSCs) has advanced rapidly in recent years; however, most studies have focused primarily on improving device efficiency rather than stability. Here, we report new ETL polymers, PPV and PPA, incorporating PDINN moieties through vinyl and ethynyl linkers, respectively. Among these materials, PPV‐M delivers the best photovoltaic performance, achieving power conversion efficiencies of 18.45% and 16.97% in D18:Y6‐BO‐ and PM6:BTP‐eC9‐based devices, respectively, surpassing those of PDINN‐based counterparts (17.79% and 16.85%). Under thermal aging at 65°C, PPV‐M‐based devices exhibited improved operational retention compared with PDINN‐based devices, with T 80 values of 637 h and 8 h, respectively. This improved efficiency and stability originate from the polymeric nature of PPV‐M, which enables smooth and uniform coverage of the photoactive layer and provides a higher glass transition temperature than the small‐molecule PDINN, thereby suppressing thermally induced molecular diffusion. These results demonstrate that polymerizing electron‐transporting units into well‐defined ETLs is an effective molecular design strategy for achieving both high efficiency and enhanced thermal stability in OSCs.