Cesium Cyclopropane Acid‐Aided Crystal Growth Enables Efficient Inorganic Perovskite Solar Cells with a High Moisture Tolerance.

While all‐inorganic halide perovskites (iHPs) are promising photovoltaic materials, the associated water sensitivity of iHPs calls for stringent humidity control to reach satisfactory photovoltaic efficiencies. Herein, we report a moisture‐insensitive perovskite formation route under ambient air for CsPbI2Br‐based iHPs via cesium cyclopropane acids (C3) as a compound introducer. With this approach, appreciably enhanced crystallization quality and moisture tolerance of CsPbI2Br are attained. The improvements are attributed to the modified evaporation enthalpy of the volatile side product of DMA‐acid initiated by Cs‐acids. As such, the water‐involving reaction is directed toward the DMA‐acids, leaving the target CsPbI2Br perovskites insensitive to ambient humidity. We highlight that by controlling the C3 concentration, the dependence of power conversion efficiency (PCE) in CsPbI2Br devices on the humidity level during perovskite film formation becomes favorably weakened, with the PCEs remaining relatively high (>15 %) associated with improved device stability for RH levels changed from 25 % to 65 %. The champion solar cells yield an impressive PCE exceeding 17 %, showing small degradations (<10 %) for 2000 hours of shell storage and 300 hours of 85/85 (temperature/humidity) tests. The demonstrated C3‐based strategy provides an enabler for improving the long‐sought moisture‐stability of iHPs toward high photovoltaic device performance. [ABSTRACT FROM AUTHOR]