Lattice Reconstruction of La Incorporated CsPbI2Br with Suppressed Phase Transition for Air-Processed All-Inorganic Perovskite Solar Cells
Inorganic CsPbI2Br halide perovskite has received extensive attention due to its excellent thermal stability and suitable bandgap for high-performance solar cells. However, CsPbI2Br can easily transform from the perovskite phase to the non-perovskite phase due to a water vapour-induced phase transition in ambient conditions, leading to a rapid degradation of device performance. Herein, we introduced lanthanum ions (La3+) into the lattice to stabilize the perovskite phase in CsPbI2Br-based all-inorganic solar cells. A power conversion efficiency of 7.72% was obtained at an optimized La3+ doping level of 2%, leading to a 22% efficiency improvement. Moreover, the La3+-doped solar cell retained 90% of its efficiency in ambient air for 400 h, showing a significantly enhanced moisture stability compared to the pristine (undoped) device. Detailed analysis indicates that La3+ ions can induce the lattice shrinking and thus inhibit the formation of non-perovskite phase, and enhance the charge carrier lifetime, which contribute to the improved moisture stability and efficiency. Our results indicate that highly stable all-inorganic solar cells can be produced in air atmosphere, showing great potential for future commercialization.