In Situ Surface Reconstruction of CsPbI3 Perovskite Films for Enhanced Phase Stability and Photovoltaic Performance

Abstract

Abstract The small ionic radius of Cs+ results in a low tolerance factor for CsPbI3 perovskite, which intrinsically triggers its spontaneous phase transition from black phase to yellow phase, severely limiting the power conversion efficiency and long-term stability of CsPbI3 perovskite solar cells. Here, we propose an in situ surface reconstruction strategy by introducing formamidinium ions (FA+) onto the CsPbI3 perovskite surface during the spin-coating process. This approach locally increases the tolerance factor in the near-surface region without altering the bulk phase, thereby raising the energy barrier for phase transition and substantially improving phase stability. Furthermore, the incorporation of FA+ boosts the perovskite crystalline quality, reduces defect density, and optimizes interface energy-level alignment. Consequently, the corresponding devices exhibit an improvement in photovoltaic performance alongside significantly enhanced stability under various harsh conditions.