Optimizing the NiOx/Au Interface via Postannealing of the All‐Inorganic CsPbIBr2 Perovskite Solar Cells for High Efficiency

All‐inorganic perovskite solar cells (PSCs) have been demonstrated to solve the thermal instability problem of organic–inorganic hybrid PSCs. Therefore, NiO x film is prepared by electron beam evaporation as a hole transport layer of all inorganic CsPbIBr 2 PSCs. Then, the postannealing is used to promote the diffusion of NiO x into the gold electrode, and enhance interface contact and reducing the electrical resistance of NiO x /Au. After optimizing NiO x /Au interface, the devices based on NiO x achieved a power conversion efficiency (PCE) of 6.7%. Furthermore, the best all‐inorganic CsPbIBr 2 PSC free of encapsulation retains 95% of initial efficiency over 100 h at 85 °C. Herein, an effective postannealing strategy is provided for optimized NiO x /Au interface to make stable and efficient all‐inorganic CsPbIBr 2 PSCs.