Balanced Crystallization Enhances Morphology and Efficiency in Binary Organic Solar Cells

Abstract Achieving high‐performance organic solar cells (OSCs) relies heavily on precise morphology optimization, a challenging task due to the intrinsic differences in crystallization kinetics and interfacial compatibility between polymer donors and small‐molecule acceptors. In this work, 2,7‐dibromonaphthalene (DBN) is introduced as an innovative solid additive that uniquely regulates crystallization in both donor and acceptor phases within the PM6:Y6 system. Unlike conventional liquid additives, which often induce excessive Y6 crystallization, DBN achieves a balanced crystallization, enhancing molecular order in PM6 while mitigating over‐aggregation in Y6. This dual‐phase effect improves light absorption, exciton generation and dissociation, charge transport, and reduces recombination losses. As a result, OSCs treated with DBN achieved a remarkable power conversion efficiency (PCE) of 18.5%, with an open‐circuit voltage (V_OC) of 0.848 V, a high short‐circuit current density (J_SC) of 28.15 mA cm⁻², and an enhanced fill factor (FF) of 77.7%. Adding an anti‐reflection MgF₂ layer further boosts efficiency to 19.0%, setting a new benchmark for PM6:Y6 binary devices. This study establishes DBN as a promising crystallization regulator and presents a robust strategy for morphology control, advancing the development of high‐performance photovoltaic applications.