Holmium rare earth metal ion incorporated and ambient-air processed all-inorganic ?-CsPbI2.5Br0.5 perovskite solar cells yielding high efficiency and stable performance

Cesium lead halide-based all inorganic perovskite solar cells (IPVSCs) are considered promising absorbers for photovoltaic applications owing to their exceptional thermal stability and suitability towards single, monolithic tandem and triple junction perovskite/perovskite tandem solar cells. However, their device performance and phase stability lag behind those of conventional organic-inorganic hybrid perovskite solar cells (HPVSCs). Here, we successfully incorporated different quantities of holmium (Ho3+) rare earth (RE) metal ions into the ?-CsPbI2.5Br0.5 perovskite. A noticeable improvement in power conversion efficiency (PCE) from 17.19% (?-CsPbI2.5Br0.5) to 19.59% was attained for the 3% HoCl3-based IPVSC device. Furthermore, our ambient-air processed 3% HoCl3-based device maintains >95% efficiency over 140 h at 30% relative humidity. This investigation shows that the RE metal ion incorporation is an effective approach for stabilizing and improving the device efficiency simultaneously.