Secondary Anti‐Solvent Treatment for Efficient 2D Dion–Jacobson Perovskite Solar Cells

Abstract Surface defects‐mediated nonradiative recombination plays a critical role in the performance and stability of perovskite solar cells (PSCs) and surface post‐treatment is widely used for efficient PSCs. However, the commonly used surface passivation strategies are one‐off and the passivation defect ability is limited, which can only solve part of the defects in the topmost surface area. Here, a secondary anti‐solvent strategy is proposed to further reduce surface defects based on conventional surface passivation for the first time. Based on this, the crystallization quality of 2D Dion–Jacobson perovskite is enhanced and the surface defects density is further reduced by nearly two orders. In addition, a gradient structure of perovskite with n = 2 phases located at the top of the film and 3D‐like phases located at the bottom of the film can also be obtained. The modulated perovskite film boosts the efficiency of 2D perovskites ( n = 5) up to 19.55%. This strategy is also very useful in other anti‐solvent processed perovskite dipping systems, which paves a promising avenue for minimizing surface defects toward highly efficient perovskite devices.