Hydrazide Derivatives for Defect Passivation in Pure CsPbI Perovskite Solar Cells.

All-inorganic CsPbI perovskite presents preeminent chemical stability and a desirable band gap as the front absorber for perovskite/silicon tandem solar cells. Unfortunately, CsPbI perovskite solar cells (PSCs) still show low efficiency due to high density of defects in solution-prepared CsPbI 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 CsPbI . Calculation and characterization results corroborate that the carboxyl and hydrazine groups in BH form strong chemical bonds with Pb 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 CsPbI -based PSCs reported to date. In addition, an unencapsulated device showed excellent stability in ambient air.