All-Inorganic CsPb2I4Br/CsPbI2Br 2D/3D Bulk Heterojunction Boosting Carbon-Based CsPbI2Br Perovskite Solar Cells with an Efficiency of Over 15%

The introduction of a two-dimensional (2D) perovskite into a three-dimensional (3D) perovskite has been proven to be effective in minimizing defect state density and improving the performance and stability of the corresponding perovskite solar cells (PSCs). However, it is a challenge to construct a 2D perovskite in 3D inorganic perovskites (CsPbX3, X = halogen) due to the limitation of the annealing temperature or the resistance of Cs+ toward the commonly used organic cation spacer. Here, we propose a strategy for the construction of an all-inorganic 2D/3D CsPb2I4Br/CsPbI2Br bulk heterojunction (BHJ) by the in situ reaction of excess PbI2 in a precursor solution with CsPbI2Br during the annealing process. The formed 2D/3D BHJ effectively passivates the defects at the surface and grain boundaries of 3D CsPbI2Br and reduces the nonradiative recombination loss in the resulting carbon-electrode-based perovskite solar cells (C-PSCs). The open-circuit voltage and efficiency of the champion C-PSCs are boosted to 1.32 V and 15.25%, respectively, which are the best results for CsPbI2Br-based C-PSCs.