Balanced Crystallization Enhances Morphology and Efficiency in Binary Organic Solar Cells

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.