Tailored Phase Transformation of CsPbI₂Br Films by Copper(II) Bromide for High-Performance All-Inorganic Perovskite Solar Cells

All-inorganic-based perovskites achieved by replacing the organic component with cesium (Cs) have drawn more attention because of their intrinsic inorganic stability. However, the cell efficiency in all-inorganic perovskite solar cells is still far below that in organic-inorganic hybrid perovskite-based devices. Here, we develop a new strategy to mediate the CsPbI₂Br crystallization by directly doping copper(II) bromide (CuBr₂) into a perovskite precursor. The incorporation of CuBr₂ played a role in retarding the crystallization dynamics process of CsPbI₂Br film, resulting in a high-quality all-inorganic perovskite film with enlarged grain size, improved carrier mobilities, and reduced trap states. The fabricated perovskite solar cells delivered a champion power conversion efficiency of 16.15%, which is the highest efficiency in CsPbI₂Br based all-inorganic perovskite solar cells and largely higher than 13.24% for pristine CsPbI₂Br based device. The developed doping method paves a new route to fabricate high-performance all-inorganic perovskite solar cells.