Surface Formamidine Cation Immobilization for Efficient FA‐Based Perovskites Solar Cells

State‐of‐the‐art perovskite solar cells (PSCs) continue to encounter stability challenges throughout their current commercialization process, primarily due to the instable organic components. Especially, surface (interface) imperfections, like the undercoordinated Pb 2+ and halide sites, further compromise the confinement of organic cations at the surface (interface) and provide a rapid pathway for ion migration and volatilization, decreasing stability and efficiency. Herein, the study has developed a surface Formamidine (FA) cation immobilization strategy through hydrogen bond effect, achieved by a post‐treatment of piperazine dihydrochloride (PDCl 2 ), to obtain stable FA‐based perovskites. The piperazine can immobilize surface FA + cation through hydrogen bond. Moreover, the post‐treatment of PDCl 2 can induce surface Cl – doping to establish strong coordinating bond with the uncoordinated Pb 2+ , reducing the imperfections of surface octahedral cage. Such a synergistic effect effectively constrains surface FA + cations, simultaneously alleviates surface lattice stress. Because of improved surface properties, the resultant perovskite demonstrates not only outstanding light/thermal stability, but also more pronounced n‐type characteristics and uniform potential distribution for improving charge transfer dynamics. Finally, the champion PSCs exhibit a significantly enhanced efficiency from 23.15% to 25.52%. Moreover, these PSCs exhibit excellent stability: retain 91% of their initial efficiency after over 1000 h maximum power point test.