Stable Perovskite Solar Cells Based on Direct Surface Passivation Employing 2D Perovskites

Surface passivation of 3D perovskites with highly stable 2D perovskite is an effective strategy to improve both performance and stability of perovskite solar cells (PSCs). Herein, a new approach has been employed for the synthesis of oleic acid and octylamine‐assisted 2D perovskites TEA2PbX4 (X = I, Br) in antisolvent and directly used them for the surface passivation of MAFAPbI3 (3D) perovskite. The grain boundary and interface are both optimized in 3D/2D perovskite by 2D perovskite to improve surface morphology. It is found that the 2D perovskite effectively suppresses carrier recombination by reducing the defect density and facilitates interfacial charge extraction through better energy‐level alignments. As a result, power conversion efficiency of PSCs is boosted up to 18.56% and 19.87% for passivation with TEA2PbI4 and TEA2PbBr4, respectively. The passivated perovskite devices exhibit good thermal, operational, and long‐term stability in an ambient environment because of the material robustness of 3D/2D hybrid perovskites.