Functionalized 2D/3D Heterojunction with Reversible Iodine‐Alkenes Reaction in Perovskite Solar Cells

Abstract Long‐term operational stability remains a big challenge for perovskite solar cells (PSCs), especially under ISOS protocol with high temperature. One key reason lies in the iodine loss issue during PSCs aging. Motived by the reversible iodine‐alkenes reaction, 3‐butenylamine (BEA) based 2D perovskite (BEA) 2 [PbBr 4 ] is used to construct a functionalized 2D/3D heterojunction in PSCs. (BEA) 2 [PbBr 4 ] can chemically adsorb photo‐generated iodine species during perovskite degradation through a typical reaction between neutral iodine and terminal alkenes, thus inhibiting iodine loss or diffusion in PSCs. Besides, owing to the reversible reaction nature, these adsorbed iodine species can be partially released slowly under heat conditions, further reacting with and eliminating potential metallic Pb 0 defects. The resulting PSCs exhibit a high efficiency of 24.5% with good operational stability even without encapsulation, retaining ≈94% of initial efficiency after MPP tracking for 2000 h at 65 °C with ISOS‐L‐2 protocol.