Surface Passivation with Tailoring Organic Potassium Salt for Efficient FAPbI₃ Perovskite Solar Cells and Modules

Abstract Passivating surface defects on perovskite films with tailored functional materials has emerged as one of the most effective strategies for achieving high‐performance perovskite solar cells (PSCs). Among existing material selections, potassium salts stand out for their effective passivation of defects surrounding perovskite grain boundaries. However, the widely used potassium salts are inorganic and only soluble in highly polar solvents, which limits their practical application for surface passivation. Herein, a novel organic potassium salt (KCFSO), with multiple organic functional groups and good solubility in low polar isopropanol, is reported to function as a post‐treatment agent for perovskite. Combined with experimental results and theoretical calculations, the formed multiple intermolecular interactions between KCFSO and perovskite are revealed to play a vital role in determining the defect passivation effect. Thus, the KCFSO‐modified film shows a more uniform surface potential distribution, dramatically decreased defect density, and improved charge transfer, leading to a champion power conversion efficiency (PCE) of 25.11%, and good stability for the derived PSCs. As a demonstration of scalability, the centimeter‐sized PSCs and 5 cm × 5 cm mini‐modules also demonstrate impressive PCEs of 24.17% and 20.18%, respectively. These findings provide insights into passivator design principles to achieve efficient and stable perovskite photovoltaics.