Regulating Crystallinity and Vertical Phase Separation via a Cyanobenzene‐Based Volatile Solid Additive Enables Efficient and Stable Binary Organic Solar Cells

ABSTRACT Halogenated benzene‐based volatile solid additives have been demonstrated to effectively regulate the morphology of active layers, thereby enhancing the performance of organic solar cells (OSCs). However, benzene‐based volatile solid additives containing a cyano group (a pseudohalogen group with chemical properties similar to those of halogen atoms) have rarely been reported. Herein, we explored the effects of three volatile solid additives: 2,5‐dibromo‐1,3‐difluorobenzene (DFBB), 5‐bromo‐2‐iodo‐1,3‐difluorobenzene (DFBI), and 4‐bromo‐2,6‐difluorobenzonitrile (DFBN) on the active layer morphology and device performance. In contrast to DFBB and DFBI containing only halogen atoms, DFBN bearing a strong electron‐withdrawing cyano group can induce the formation of ordered molecular packing, high crystallinity, and favorable vertical phase distribution in the D18:L8‐BO blend, leading to a significant improvement in charge transport and collection efficiency. Consequently, the DFBN‐treated D18:L8‐BO device achieved a power conversion efficiency (PCE) of 20.33%, along with excellent thermal stability and photostability. Furthermore, DFBN exhibits superior universality in other OSC systems. This study demonstrates that the introduction of cyanobenzene‐based solid additives is a facile and effective strategy for obtaining high‐performance OSCs.