Buried Interface Engineering‐Assisted Defects Control and Crystallization Manipulation Enables Stable Perovskite Solar Cells with Efficiency Exceeding 25%

Abstract The presence of various defects within the electron transport layer (ETL), the perovskite (PVK) layer, and their interfaces significantly affects the efficiency, hysteresis, and stability of perovskite solar cells (PSCs) in n–i–p structure. Herein, a defect passivation strategy employing potassium 4‐methoxysalicylate (MSAK) is utilized to efficiently modulate the defects in the ETL, PVK, and ETL/PVK interface. The functional groups −COO− and −OH in MSAK molecules, along with the K⁺ cations, effectively reduce the defects of tin oxide (SnO₂) and improve the electron transport properties. Importantly, the MSAK‐SnO₂ provides a favorable substrate for the growth of highly crystallization and dense perovskite layers. The MSAK molecules also significantly passivate the bottom interface defects of the PVK layer by coordinating with under‐coordinated Pb²⁺ ions. Furthermore, K⁺ cations can migrate into the PVK layer, further enhancing crystallization and improving the photovoltaic performance of PSC devices. PSCs fabricated using the defect passivation strategy based on MSAK achieve a remarkable power conversion efficiency (PCE) of 25.47%, alongside reduced hysteresis and enhanced stability. After being stored under ambient conditions for 60 days, the device with MSAK maintains nearly 90% of its initial PCE, whereas the PCE of the pristine device decreases to 69.7% after aging.