Two‐Dimensional Metal–Organic Frameworks‐Based Grain Termination Strategy Enables High‐Efficiency Perovskite Photovoltaics with Enhanced Moisture and Thermal Stability

Abstract Perovskite degradation induced by surface defects and imperfect grain boundaries of films seriously damages the performance of perovskite solar cells (PSCs). Meanwhile, conventional organic molecules cannot maintain the long‐time passivation effects under the stimulation of external environmental factors. Here, efficient and stable grain passivation in perovskite films is realized by preparing formic acid‐functionalized 2D metal–organic frameworks (MOFs) as the terminated agent. Through robust interactions between exposed active sites and PbI 2 , the 2D MOFs tightly caps the surface of PbI 2 ‐terminated perovskite grains to stabilize the perovskite phases and aids the adhesion of adjacent grains. The MOFs mainly distributed at the grain boundaries of the perovskite film is directly observed at the microscopic scale. The modified perovskite films have regular morphology, lower defect density, and superior optoelectronic properties. Benefiting from the suppressed charge recombination and faster charge extraction, a power conversion efficiency of 21.28% is achieved for the best‐performing PSC device. The unencapsulated PSCs with the MOFs modification maintain 88% and 81% of their initial efficiency after 750 h heating at 85 ° C under N 2 atmosphere and more than 1000 h storage in ambient environment (25 ° C, RH ≈ 40%), respectively.