Extended and Balanced Crystallization Kinetics via Electrostatic Potential Distribution Manipulation of Solid Additives for Organic Solar Cells Reaching 20.89% Efficiency

ABSTRACT An ideal film morphology featuring a high‐quality donor–acceptor double‐fibril interpenetrating network is crucial for achieving efficient exciton dissociation and charge transport, which are key to realizing high‐performance organic solar cells (OSCs). However, the inherent differences in crystallization kinetics between donor and acceptor materials make this a significant challenge. Herein, a series of simple‐structured chlorine‐substituted benzo[b]thiophene isomers, namely 4‐Cl‐BT, 5‐Cl‐BT, and 6‐Cl‐BT, with various spatial electrostatic potential (ESP) distributions, are designed for the regulation of crystallization kinetics. Owing to its favorable spatial ESP distribution, 5‐Cl‐BT exhibits more synergistic dipole–dipole interactions and dispersion forces, thereby strengthening its intermolecular interactions with PM6 and L8‐BO. This facilitates the formation of ordered molecular packing and enhanced phase separation, and promoting balanced crystallization kinetics during the film formation process. Consequently, the PM6:L8‐BO‐based OSCs with 5‐Cl‐BT treatment achieve a higher efficiency of 19.34%. More impressively, the D18‐based ternary devices treated with 5‐Cl‐BT deliver a remarkable efficiency of 20.89%, with an excellent fill factor of 82.56%, which ranks among the best values reported so far. This work highlights the critical role of rationally regulating the spatial ESP distribution of solid additives in modulating the crystallization kinetics of donor and acceptor materials and achieving ideal film morphology and efficient OSCs.