Enhancing High-Humidity Stability of CsPbI₃ Perovskite Solar Cells Through Strong Bidentate Ligand Coordination

The stability of inorganic CsPbI₃ perovskite solar cells (IPSCs) has been greatly limited by their accelerated degradation in a high-humidity environment. In this investigation, we design a defect-passivation approach using monodentate p-toluenesulfonyl hydrazide (TSH) and a bidentate ligand, 2-amino-6-methoxybenzothiazole (AMBT), which boosts the humidity resistance of CsPbI₃ perovskite under 80% relative humidity (RH). Based on density-functional-theory calculations, it has been found that AMBT has a significantly higher binding energy of -1.91 eV with respect to CsPbI₃ than that of TSH with a binding energy of -0.98 eV, consistent with their extremely stable Pb-N and Pb─O coordination bonds, ascertained by XPS and FTIR spectroscopy. Surface modification of AMBT effectively promotes crystal perfection, decreases trap state, and extends carrier lifetime, yielding a maximum power conversion efficiency (PCE) of 18.52% with a high fill factor of 84.35%. Unencapsulated device structures with 80% RH maintain their β-phase structure for over 60 min, and corresponding IPSCs maintain 40% of their initial efficiency over 10 days, being among the highest humidity-resistance strengths for CsPbI₃ perovskite-based devices. Our results provide a powerful strategy for developing moisture-independent CsPbI₃ perovskite solar cells.