Stabilized Intermediate Phase Via Pseudo‐Halide Anions Toward Highly Efficient and Light‐Soaking Stable Perovskite Solar Cells

Abstract Long‐term stability remains challenging due to persistent defects within the perovskite material, particularly at buried interfaces. Strategies to address these issues have focused on refining interfaces and managing residual lead iodide (PbI 2 ), which impedes electron transport and compromises stability under prolonged light exposure. This study explores the impact of lead formate (PbFo 2 ) treatment on SnO 2 electron transporting layer (ETL) substrates and its subsequent influence on the performance of perovskite solar cells (PSCs). The carboxylate functionality of Fo − ions exerts multifaceted effects, influencing not only the electrical properties of the SnO 2 ETL but also the morphological characteristics and crystallization mechanism of the overlying perovskite film. The ionized Fo − ions aid in forming bulk perovskite as intermediate phases during the perovskite crystallization. By stabilizing intermediate phases, their incorporation suppresses indiscriminate phase transitions from δ ‐phase to α ‐phase perovskite, ensuring the production of highly crystalline pure α ‐phase perovskite with alleviated tensile strain throughout the perovskite film, particularly near the buried interface. Consequently, the strategy showcases enhanced performance with a power conversion efficiency (PCE) of 25.69% and enables a refined buried interface, devoid of residual PbI 2 , ensuring long‐term stability under continuous light‐soaking for 1,000 h. Overall, PbFo 2 treatment stands as a pioneering approach poised to expedite commercialization.