Synergistic Full‐Scale Defect Passivation Enables High‐Efficiency and Stable Perovskite Solar Cells

Abstract Despite remarkable progress in perovskite solar cells (PSCs), the unsatisfying stability strongly interrelated with the defect density remains the main obstacle for commercialization. Herein, a synergetic defect passivation method is judiciously designed that consists of a precursor engineering strategy based on an ionic liquid 1‐butylsulfonate‐3‐methylimidazolium dihydrogen phosphate (BMDP), and two‐stage annealing (TSA) treatment to sufficiently passivate defects and enhance performance further. It is found that the multifunctional groups from BMDP have strong chemical interactions and form chelated complexes with perovskite components thus effectively passivating the intrinsic defects. Synergized by the sequential TSA treatment, the formed hydrophobic complexes can be precisely controlled with filling along grain boundaries (GBs) and on surfaces, leading to a wrapping of perovskite grains and significant passivation of GBs. Consequently, both deep‐ and shallow‐level defects in the bulk, at GBs and surface are sufficiently passivated, resulting in a champion efficiency of 24.20%. Impressively, the resultant unencapsulated films and corresponding devices exhibit admirable stability with maintaining 83.9% of initial composition for 4000 h of aging in moist air, 81.7% original structure after continuous heating for 1600 h, and 97% initial power conversion efficiency for 1000 h under continuous illumination. This work provides an efficient strategy toward improved efficiency and stability PSCs.