Enhancing High‐Humidity Stability of CsPbI ₃ Perovskite Solar Cells Through Strong Bidentate Ligand Coordination

ABSTRACT The stability of inorganic CsPbI ₃ 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 CsPbI ₃ 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 CsPbI ₃ 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 CsPbI ₃ perovskite‐based devices. Our results provide a powerful strategy for developing moisture‐independent CsPbI ₃ perovskite solar cells.