Ultra-smooth CsPbI2Br film via programmable crystallization process for high-efficiency inorganic perovskite solar cells

Abstract CsPbI2Br is an ideal inorganic perovskite material with a reasonable bandgap for solar cell applications because of its advantage of superior thermal and phase stability. However, the performance of CsPbI2Br based solar cells highly relied on the perovskite crystallization process along with the interfacial contact engineering process between CsPbI2Br perovskite and charge-transporting layers. In this work, a programmable crystallization method is developed to obtain ultra-smooth CsPbI2Br perovskite film with a well-engineered contact interface in perovskite solar cells. This method combines a pre-stand-by process with a programmable gradient thermal engineering process, which mediates the crystal growth dynamics process of CsPbI2Br perovskite by controlling the release of dimethyl sulfoxide (DMSO) from its coordinates with the perovskite film, leading to high-quality CsPbI2Br film with large-scale crystalline grains, reduced surface roughness, and low trap density. Fabricated perovskite devices based on CsPbI2Br film obtained by this method deliver power conversion efficiency of 14.55%; meanwhile, the encapsulated CsPbI2Br perovskite device achieves a maximum efficiency of 15.07%. This decent solar conversion efficiency demonstrates the effectiveness of the programmable crystallization method used in this work, which shows great potential as a universal approach in obtaining high-quality CsPbI2Br perovskite films for fabricating high-efficiency inorganic perovskite solar cells.