Approaches for thermodynamically stabilized CsPbI3 solar cells

With its suitable bandgap (<1.73 eV), excellent optoelectronic properties and ideal thermo-stability, cesium lead halide, CsPbI3, is a promising candidate for next-generation photovoltaics (PVs). However, its instable structure (perovskite black phase can transform to non-perovskite yellow phase at room temperature) limits further development. Since the first report in 2014, much efforts have been made to stabilize the structure (black phase), and the corresponding inorganic perovskite solar cells (PSCs) have made great progress in terms of power conversion efficiency (PCE) which increased from 0.09% to 19.03%. In this review, we summarize the intrinsical instability of CsPbI3, and discuss the recent works in improving the stability of CsPbI3 from four aspects: (1) ionic incorporation; (2) metastable phases; (3) reduced dimensions; (4) steric hindrance. Finally, the problems that still exist and the possible directions for solving them are presented.