Trimeric Acceptors with Fine‐Tuned Alkyl‐Linkage Sites for 20.23% Efficiency and Stable Organic Solar Cells

Giant-molecule acceptors (GMAs) have been proven to improve power-conversion-efficiency (PCE) and stability of organic solar cells (OSCs), while most high-performance GMAs only attach two monomers and primarily exhibit the properties of their monomer precursors. Herein, we develop four trimeric GMAs (named 3Y-site, including wing-sites-linked 3Y-Wing, end-sites-linked 3Y-End, hybrid wing/end-sites-linked 3Y-EWE and 3Y-WEW) with the same alkylated linker but different linking sites to fine-tune molecular optoelectronic properties. Among them, 3Y-Wing with a superior planarity and extensibility possesses broadened absorption, better crystallinity, superior packing, and higher glass transition temperature, resulting in an optimized phase separation. The optimized devices with binary PM6:3Y-Wing and ternary PM6:L8-BO:3Y-Wing achieve both champion PCEs of 15.0% and 19.1%, respectively, along with enhanced light, thermal, and storage stabilities, outperforming devices based on all other 3Y-site counterparts. In the classic D18:L8-BO host system, the effectiveness of 3Y-Wing in boosting PCE is further validated, and the resulted ternary devices deliver an excellent PCE of 20.23%, setting an efficiency record among the reported trimeric GMAs. Moreover, the 3Y-Wing based OSCs offer a better balance of high PCE and stability, further distinguishing them within 3Y-site series. Our developed wing-sites-linked trimeric 3Y-Wing is a promising candidate to achieve both high device efficiency and stability.