Hydrazide Derivatives for Defect Passivation in Pure CsPbI₃ Perovskite Solar Cells

All-inorganic CsPbI₃ perovskite presents preeminent chemical stability and a desirable band gap as the front absorber for perovskite/silicon tandem solar cells. Unfortunately, CsPbI₃ perovskite solar cells (PSCs) still show low efficiency due to high density of defects in solution-prepared CsPbI₃ films. Herein, three kinds of hydrazide derivatives (benzoyl hydrazine (BH), formohydrazide (FH) and benzamide (BA)) are designed to reduce the defect density and stabilize the phase of CsPbI₃ . Calculation and characterization results corroborate that the carboxyl and hydrazine groups in BH form strong chemical bonds with Pb²⁺ ions, resulting in synergetic double coordination. In addition, the hydrazine group in the BH also forms a hydrogen bond with iodine to assist the coordination. Consequently, a high efficiency of 20.47 % is achieved, which is the highest PCE among all pure CsPbI₃ -based PSCs reported to date. In addition, an unencapsulated device showed excellent stability in ambient air.