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

ABSTRACT 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.