A Dual‐Functional Coordination Additive for Defect Passivation and Large‐Grain Formation in Perovskite Film

Abstract Regulating the crystallization kinetics of perovskite films to achieve large, low‐defect grains is essential for enhancing the performance of perovskite solar cells (PSCs). However, controlling the growth of micron‐sized perovskite grains remains a significant challenge. In this study, 4‐Fluorobenzenesulfonamide (4‐FBSO) is introduced into the perovskite precursor to modulate the crystallization process. Experimental results demonstrate that the 4‐FBSO effectively slows down crystallization and promotes the coalescence of small grains, leading to the formation of high‐quality perovskite films with grain sizes over 1 µm. Density functional theory (DFT) calculations suggest that both ends of the 4‐FBSO molecule coordinate with Pb 2+ ions in the perovskite, creating “grain boundary adhesion” between adjacent grains. This interaction supports the orderly growth of large grains. As a result, the fabricated device achieves an impressive power conversion efficiency (PCE) of 25.4%. This work provides a new approach to controlling the perovskite crystallization kinetics and offers valuable insights into the molecular mechanism behind grain growth.