In Situ Surface Reconstruction of FA-Based Perovskites with Rigid Molecule for Efficient and Stable Photovoltaics

Abstract In the pursuit of commercial perovskite solar cells (PSCs), formamidinium lead iodide (FAPbI3) has become a high-potential material. However, surface FA cations readily deprotonate into volatile amines under light and thermal stress, which leads to the formation of defects states on the perovskite surface. Herein, a deprotonation reaction of surface FA+ is exploited to in situ reconstruct a more stable structure, where the loosely bound surface FA+ cations are replaced by stable triethylene diamine (TEDA) cations. Moreover, TEDA+ cations anchor to the perovskite surface, forming a uniform layer and thereby generating a strong vertical dipole moment at the interface. This dipole moment produces a uniform electric field that repels minority carriers while allowing majority carriers to pass through. The resulting perovskite film exhibited uniform photoluminescence distribution, suppressed defect states, and optimized energy level alignment. Finally, the TEDA-treated PSCs exhibit an enhanced power conversion efficiency (PCE) of 25.11% with an increased VOC of 1.159 V. Moreover, the TEDA-treated PSCs demonstrate good stability, maintaining 96.52% of their initial PCE after 500 h under a maximum power point (MPP) test.