Rationalizing Star‐Shaped Nonfullerene Acceptors in Ternary Organic Solar Cells: Morphology Mediation Facilitates Exciton and Carrier Dynamics

Abstract Star‐shaped trimeric acceptors have garnered increasing attention in organic solar cells (OSCs), yet a mechanistic gap exists on regulation of morphology and carrier dynamics. Herein, a nonfullerene acceptor named BTF‐Trimer bearing a benzotrifuran core with more electronegative oxygen atoms is newly designed, which fosters intermolecular interactions with both polymer donors and small‐molecule acceptors. BTF‐Trimer possesses reduced aggregation tendencies and a high glass transition temperature, which are conducive to inhibiting excessive aggregation of acceptor phases and stabilizing film morphology, respectively. Notably, BTF‐Trimer as morphology mediator strengthened host donor‐acceptor compatibility in ternary blend active layers, forming dual‐fibril interpenetrating networks that promoted exciton dissociation and hole transfer as well as alleviated bimolecular recombination in devices. Consequently, the power conversion efficiency and T 70 (the time required to reach 70% of the initial efficiency) lifetime of the ternary OSCs in an Ar atmosphere achieved 19.13% and ≈2800 h, respectively. This study highlights the distinctive merits of star‐shaped acceptors as to suppress over‐crystallization and enhance phase continuity, offering insights into the interplay of phase‐separated morphology and carrier dynamics, which plays a critical role in ternary devices.