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 Cs 2 PbI 2 Cl 2 –CsPbI 2.5 Br 0.5 perovskite solar cell was successfully developed to address this issue. The 2D Cs 2 PbI 2 Cl 2 phase distributed among the grain boundaries of the 3D CsPbI 3– x Br x grains. The existence of Cs 2 PbI 2 Cl 2 effectively facilitated the (100) preferential crystal orientation of the CsPbI 2.5 Br 0.5 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 cm 2 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.