The Polymer Society of Korea

Abstract

Solution-state pre-aggregation critically governs nucleation processes, phase separation, and molecular ordering during active layer formation in organic solar cells (OSCs). Nevertheless, such aggregation behavior is rarely achieved in non-fullerene acceptors (NFAs), restricting the formation of highly ordered microstructures. Here, we report a newly designed NFA, termed SHA, featuring unsaturated branched side chains as an unconventional molecular design. These unsaturated branched side chains induce extraordinarily strong aggregation in solution, which is efficiently propagated into the solid state, producing compact molecular packing, enhanced crystallinity, and a high density of crystalline domains in thin films. Owing to these microstructural advantages, SHA-based ternary OSCs exhibit markedly improved photovoltaic performance, reaching a power conversion efficiency of 19.7%. This study identifies unsaturated branched side chains as a previously unrecognized design dimension and demonstrates their general role as a pre-aggregation-mediated seeding effect for realizing high-efficiency OSCs.