Facile Hydrogen-Bonding Assisted Crystallization Modulation for Large-area High-quality CsPbI₂ Br Films and Efficient...

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 CsPbI₂ 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 CsPbI₂ Br from ionic precursors but also widens the film processing window, thus enabling to fabricate large-area high-quality phase-pure CsPbI₂ Br film under benign conditions. Combining with stable dopant-free poly(3-hexylthiophene), the CsPbI₂ Br solar cells achieve the record-high efficiencies of 18.14 % and 16.46 % for 0.1 cm² and 1 cm² 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.