Calix[8]arene‐Tethered Dendritic Octamer Acceptor with Ultrahigh Molecular Weight Enables 20.7% Efficiency Organic Solar Cells with Exceptional Stability

Increasing the molecular weight of the acceptor is an effective strategy to suppress excessive crystallization and molecular diffusion, thereby addressing morphological challenges in organic solar cells (OSCs). Therefore, designing high‐molecular‐weight acceptor with well‐defined structures is crucial for achieving efficient and stable OSCs towards commercialization. Herein, we report a calix[8]arene‐tethered dendritic octameric acceptor with a molecular weight of 14243 g/mol and a well‐defined structure. Owing to its dendritic structure, which facilitates multidimensional charge transport and enhances both molecular interactions, C8‐IC can operate efficiently, achieving a high power conversion efficiency (PCE) of 18.7%, despite its lower crystallinity. Moreover, it effectively acts as a crystallization manipulator, regulating the interaction and crystallization within the D18:L8‐BO system. This optimizes charge management in the ternary system, achieving a state‐of‐the‐art efficiency of 20.7%. To our knowledge, this is among the highest efficiency values reported for OSCs based on dendritic acceptors. Besides, the ultrahigh molecular weight of the dendritic acceptor effectively increases the glass transition temperature (Tg), inhibits molecular diffusion, and stabilizes the morphology, leading to significantly improved device stability. This work presents high‐performance OSCs based on a dendritic acceptor with ultrahigh molecule weight and provides valuable insights into the design of acceptor materials for highly stable OSCs.