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.