Heptafluoropentane Side Chain‐Engineered Acceptor, a Morphological Modulator for High‐Performance Ternary Organic Solar Cells ^†

Comprehensive Summary Organic solar cells (OSCs) leveraging non‐fullerene acceptors (NFAs) have achieved power conversion efficiencies (PCEs) exceeding 20%, yet their performance critically depends on the nanoscale morphology of the bulk heterojunction (BHJ). Ternary blending is a promising strategy for enhancing photovoltaic parameters and morphology control, but simultaneously optimizing phase separation size, vertical phase distribution, and crystallinity remains challenging. Herein, a new L8‐BO‐derived non‐fullerene acceptor, namely BTP‐ HFCP, featuring a heptafluorocyclopentenyloxy–octyl side chain was developed. When it was integrated as a third component into the D18:L8‐BO binary system, BTP‐HFCP acts as an effective morphological modulator. Adv. characterizations reveal that the ternary device exhibits a significantly enhanced vertical phase distribution, optimal phase separation and balanced crystallinity, thereby improving chargecollection and reducing recombination. Consequently, the ternary OSC achieves a champion PCE of 19.32%, surpassing the binary OSC. This work demonstrates that heptafluoropentane side‐chain engineering of the third component provides a rational molecular design strategy for precise morphology control in high efficiency ternary OSCs.