Hydrazide derivatives for defect passivation in pure CsPbI${}_3$ perovskite solar cells

All-inorganic CsPbI${}_3$ perovskite presents preeminent chemical stability and a desirable band gap as the front absorber for perovskite/silicon tandem solar cells. Unfortunately, CsPbI${}_3$ perovskite solar cells (PSCs) still show low efficiency due to high density of defects in solution-prepared CsPbI${}_3$ 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${}_3$. Calculation and characterization results corroborate that the carboxyl and hydrazine groups in BH form strong chemical bonds with Pb${}^{2+}$ 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${}_3$-based PSCs reported to date. In addition, an unencapsulated device showed excellent stability in ambient air. (© 2022 Wiley‐VCH GmbH)