2D-3D Cs2PbI2Cl2-CsPbI2.5Br0.5 Mixed-Dimensional Films for All-Inorganic Perovskite Solar Cells with Enhanced Efficiency and Stability.

The phase instability of cesium lead halide perovskite is still a substantial challenge hindering its application. A 2D-3D all-inorganic Cs2PbI2Cl2-CsPbI2.5Br0.5 perovskite solar cell was successfully developed to address this issue. The 2D Cs2PbI2Cl2 phase distributed among the grain boundaries of the 3D CsPbI3-xBrx grains. The existence of Cs2PbI2Cl2 effectively facilitated the (100) preferential crystal orientation of the CsPbI2.5Br0.5 crystals, promoting the carrier transport. The smooth transition region between the (003)2D//(001)3D interface indicated the formation of a 2D-3D heterostructure. Due to the improved crystal quality, high uniformity, and repeatability, the efficiency of the solar cells with areas of 0.09, 1, and 2 cm2 significantly improved to 15.09%, 12.74%, and 10.01%, respectively. The power conversion efficiency (PCE) retained 95.3% of the initial efficiency after 60 days in a nitrogen atmosphere at room temperature and 80% of the initial efficiency at a humidity of 70 ± 10% relative humidity (RH) under continuous heating at 80 °C for 12 h.