Defect Suppression via Tailoring Functionalized Additives for Efficient and Stable CsPbI ₃ Perovskite Solar Cells

Cesium lead iodide perovskites offer promising stability and a bandgap near 1.7 eV, making them suitable as the top cell in tandem solar cells. However, the inorganic perovskite films suffer from a high defect density and substantial recombination losses, undermining their optoelectronic performances. Here, by activating the aromatic system, we develop 4‐methoxybenzoylhydrazine (MeOBH)‐modified CsPbI 3 film with regulated crystallinity, suppressed non‐radiative recombination, and improved interfacial energetic alignment. The resultant inorganic perovskite solar cells achieved a power conversion efficiency of 20.95%, along with enhanced phase stability owing to the strong coordination interaction between the lead cation and the hydrazide group. Encapsulated devices retain 90.4% of the initial performance after 624 h of maximum power point operation under the ISOS‐L‐1I protocol.