Geometry Engineering of V/Y/X-Shaped Nonfullerene Acceptors for Ternary Organic Photovoltaics

Ternary bulk heterojunction (BHJ) organic solar cells (OSCs) hold great promise for enhancing photovoltaic performance, yet the influence of the third component's molecular geometry remains underexplored. Herein, we designed and synthesized a series of benzene-cored nonfullerene acceptors (NFAs) with V-, Y-, and X-shaped configurations-B2D-DFIC, B3D-DFIC, and B4D-DFIC-via an atom-economical direct CH arylation strategy. These NFAs exhibit complementary absorption and cascaded energy levels with the PM6:Y6 host system, enabling optimized morphology and enhanced exciton dissociation. Notably, the highly symmetric X-shaped B4D-DFIC promotes face-on molecular packing and forms a well-interpenetrated fibrous network, leading to a remarkable increase in power conversion efficiency (PCE) from 15.42% to 16.65%, along with improved charge carrier balance (μ_h/μ_e = 0.92) and reduced recombination. Our work establishes a clear geometry-performance relationship, demonstrating that enhanced molecular symmetry (V → Y → X) systematically improves device performance through optimized molecular ordering and charge transport pathways.