Post‐device Dimethylamine Treatment Enables Stable and Efficient Perovskite Solar Cells

Abstract The incorporation of organic ligands via post‐device treatment is an effective strategy to improve the stability of perovskite solar cells (PSCs). Although the active area is protected by metal electrode under post‐treatment, the aggression of post‐treatment ligands into active area cannot be avoided thoroughly. Unfortunately, the size of long‐chain amines is too large, and the three‐dimensional (3D) perovskite cannot maintain its 3D perovskite structure once the cation substitution occurs during the post‐treatment. Despite that the low‐dimensional (LD) perovskites are beneficial to stability, long‐chain amines are harmful to carrier transport in PSCs. Here, we introduce dimethylamine (DMA), a slightly oversized cation that can be doped into 3D perovskite structure, for post‐device treatment to improve the efficiency and stability of PSCs. After exposure to DMA gas, the inactive area of Cs/FA/MA mixed cation perovskite device that is not covered by metal electrode is converted into LD perovskite, passivating the defects of 3D perovskite in the active region, suppressing non‐radiation recombination and ion migration. As a result, we achieved a power conversion efficiency (PCE) of 22.29 % with negligible hysteresis and better stability after DMA post‐treatment, which is much higher than that (20.40 %) of the control device.