Optimizing Molecular Packing and Film Morphology in Organic Solar Cells via Additive‐Modulated Growth Processes

Abstract Controlling the packing feature and film morphology of active layers is the precondition for achieving highly efficient organic solar cells (OSCs). The growth transition of donors and acceptors from solution to solid films plays an intrinsic role in shaping these features. In this study, two simple additives, cyanobenzene (CNB) and 1,4‐dicyanobenzene (DCNB), are presented to modulate the growth process of active layers to investigate the impact of growth behaviors on molecule packing quality, film morphology, and device performances. Both additives prolong the nucleation and growth period of active layers, resulting in improved molecular packing quality, domain purity, and crystallization. This optimization enhances charge extraction efficiency as well as reduces charge recombination losses. Consequently, devices based on D18:BTP‐eC9‐4F processed with additives obtain a 19.43% power conversion efficiency (PCE). Furthermore, a PCE of 14.35% is achieved for bladed‐coated organic solar modules on 5 cm × 5 cm substrates. These findings underscore the importance of growth processes on film quality and illustrate their fundamental relationship, which promises further advancements in OSC technology.