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

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 T₇₀ (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.