Facile Hydrogen‐Bonding Assisted Crystallization Modulation for Large‐area High‐quality CsPbI2Br Films and Efficient Solar Cells

Abstract The thermally stable inorganic cesium‐based perovskites promise efficient and stable photovoltaics. Unfortunately, the strong ionic bonds lead to uncontrollable rapid crystallization, making it difficult in fabricating large‐area black‐phase film for photovoltaics. Herein, we developed a facile hydrogen‐bonding assisted strategy for modulating the crystallization of CsPbI 2 Br to achieve uniform large‐area phase‐pure films with much‐reduced defects. The simple addition of methylamine acetate in precursors not only promotes the formation of intermediate phase via hydrogen bonding to circumvent the direct crystallization of CsPbI 2 Br from ionic precursors but also widens the film processing window, thus enabling to fabricate large‐area high‐quality phase‐pure CsPbI 2 Br film under benign conditions. Combining with stable dopant‐free poly(3‐hexylthiophene), the CsPbI 2 Br solar cells achieve the record‐high efficiencies of 18.14 % and 16.46 % for 0.1 cm 2 and 1 cm 2 active area, respectively. The obtained high efficiency of 38.24 % under 1000 lux illumination suggests its potential in indoor photovoltaics for powering the Internet of Things, etc.