Manipulating Molecular Packing Mode and Excited‐State Dynamics via Twisted Conjugated Groups for High‐Performance Organic Solar Cells

ABSTRACT Enhancing open‐circuit voltage ( V OC​ ) in organic solar cells (OSCs) remains a critical challenge due to substantial nonradiative energy losses (Δ E nr​ ). Here, we introduce a tetraphenylethylene (TPE)‐functionalized acceptor, L8‐TPE, that selectively modulates molecular packing to reduce Δ E nr​ and enhance device performance. Single‐crystal analysis reveals that the TPE moiety mitigates end‐to‐central π – π stacking, reducing aggregation‐induced quenching while maintaining efficient charge transport. Therefore, L8‐TPE exhibits a significantly enhanced photoluminescence quantum yield of 18.1%, compared with 10.2% for L8‐BO, reflecting suppressed nonradiative decay. When incorporated as a guest acceptor in D18:L8‐BO‐based ternary OSCs, the devices exhibit a reduced Δ E nr​ of 0.195 eV, an elevated V OC ​ of 0.926 V, and a power conversion efficiency of 20.6%. Theoretical calculations, and photophysical/transient analyses, indicate that the improved device performance is associated with reductions in singlet–triplet energy gaps and enhanced spin–orbit coupling (SOC), as well as prolonged photoluminescence lifetime, reduced energetic disorder and electron–phonon coupling, and optimized charge dynamics. X‐ray scattering further reveals that the ternary blend maintains favorable face‐on orientations and well‐intermixed domains, facilitating exciton migration. This work demonstrates that rational side‐chain engineering can tune molecular packing and excited‐state behavior, providing a useful molecular design for suppressing nonradiative losses and enhancing OSC performance.