Tetragonal CsPb ₂ Br ₅ nanosheets, involving lateral shape evolution, were obtained via oriented attachment of orthorhombic CsPbBr ₃ nanocubes.

MXenes have been demonstrated as a potential candidate in the field of photovoltaics and energy storage owing to their high transmittance, metallic conductivity and tunable work function. In this work, we introduce a two-dimensional (2D) structure of Ti₃C₂-MXene nanosheets into all inorganic CsPbBr₃ solar cells as an interlayer to realize a better interfacial energy level alignment, which helps to eliminate the energy level mismatch, accelerate the hole extraction and reduce the recombination at the interface of perovskite/carbon electrode. In addition, the functional groups such as O existing in the surface of Ti₃C₂-MXene nanosheets also provide strong interactions between the MXene and under-coordinated Pb atoms, which remarkably reduces the deep trap defects in the CsPbBr₃ films. The device with the Ti₃C₂-MXene interlayer shows an impressive initial power conversion efficiency of 9.01% and long-term stability for over 1900 hours in a moisture environment and more than 600 hours under thermal conditions.