Complex Makes It Powerful: From Unidirectional to Bidirectional via Synergistic Volatile Solid Additives Enabling 20.16% Efficient and Stable Organic Solar Cells

ABSTRACT Traditional volatile solid additives (VSAs) often regulate only the donor or acceptor phase, limiting synergistic microstructure optimization. Here, we report two halogenated nitrobenzene‐based additives, 3,5‐dichloronitrobenzene (DCNB) and 3,5‐dibromonitrobenzene (DBNB), that enable bidirectional regulation of both components. Owing to their anisotropic electrostatic potential and large dipole moments, they simultaneously promote ordered crystallization of donor D18 and enhanced packing of acceptor L8‐BO. Characterizations confirm improved molecular ordering and optimized phase separation, forming a favorable interpenetrating network. Consequently, D18:L8‐BO devices with DCNB and DBNB achieve power conversion efficiencies of 20.16% and 19.80%, respectively, versus 17.87% for the control. The 20.16% efficiency ranks among the highest for binary OSCs processed with volatile solid additives. Charge dynamics and transient absorption spectroscopy reveal enhanced exciton dissociation, suppressed recombination, and accelerated interfacial hole transfer. This strategy also shows broad universality across multiple D‐A systems, retaining >90% initial efficiency after 1000 h. This work unveils a bidirectional synergistic regulation mechanism and offers new insights into morphology engineering for stable, high‐efficiency OSCs.