MAI\nPost-treatment\nto Promote Uniform Halide Distribution\nfor Efficient Carbon-Based CsPbI<sub>2</sub>Br Perovskite Solar Cells

Hole-transport-layer-free carbon-based\nCsPbI<sub>2</sub>Br all-inorganic\nperovskite solar cells (C–IPSCs) have garnered significant\nattention due to their low cost and remarkable thermal stability.\nHowever, the power conversion efficiency (PCE) is still low. In this\nstudy, we observed an inhomogeneous halide distribution in the out-of-plane\ndirection of CsPbI<sub>2</sub>Br films. MAI (methylammonium iodide)\npost-treatment improved the distribution of halides and enhanced the\nquality of the CsPbI<sub>2</sub>Br perovskite film through recrystallization.\nMoreover, the energy level of the device exhibits a gradient alignment,\nwhile the control exhibits an energy barrier caused by inhomogeneous\nhalide distribution. This improvement obviously facilitates the extraction\nof electrons and holes, minimizes nonradiative carrier recombination,\nand ultimately enhances the overall performance of the device. The\ndevice exhibits a high conversion efficiency of 15.21%, an open circuit\nvoltage (<i>V</i><sub>oc</sub>) of 1.34 V, and a fill factor\nof 73.5%. Additionally, the PCE of the device treated with MAI remained\nat 75.26% of its original value after 300 h of storage in ambient\nair without encapsulation.