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 CsPbIBr2 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 CsPbIBr2 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 CsPbIBr2 PSCs.
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