Low‐Temperature Processed Carbon Electrode Based Inorganic Perovskite Solar Cells with Enhanced Photovoltaic Performance and Stability

All‐inorganic perovskite solar cells have drawn widespread attention for its superior thermal stability. Carbon‐based devices are promising to demonstrate excellent long‐term operational stability due to the hydrophobicity of carbon materials and the abandon of organic hole‐transporting materials (HTMs). However, the difficulty to control the crystallinity process and the poor morphology leads to serious non‐radiative recombination, resulting in low V_OC and PCE. In this paper, the crystal formation process of all‐inorganic perovskites is controlled with a facile composition engineering strategy. By bromide incorporation, high‐quality perovskite films with large grain and fewer grain boundaries are achieved. As‐prepared perovskite films demonstrate longer carrier lifetime, contributing to lower energy loss and better device performance. Fabricated carbon‐based HTM‐free PVSCs with CsPbI_2.33Br_0.67 perovskite realized champion power conversion efficiency of 12.40%, superior to 8.80% of CsPbI₃‐based devices, which is one of the highest efficiencies reported for the carbon‐based all‐inorganic PVSCs to date. The high V_OC of 1.01 V and FF of 70.98% indicate the significance of this composition engineering method. Moreover, fabricated carbon‐based devices exhibit excellent stability, unencapsulated device retains over 90% of its initial efficiency under continuous one sun illumination for 250 hours in N₂ atmosphere and keeps ~84% of its original value after stored in ambient environment with RH 15%-20% for 200 hours. This work provides a facile way to fabricate high‐performance and stable carbon‐based all‐inorganic perovskite solar cells.