Highly Stable All‐Inorganic Perovskite Solar Cells Processed at Low Temperature

All‐inorganic perovskites such as cesium lead bromide (CsPbBr 3 ) can show much better stability than organic–inorganic hybrid perovskite materials in ambient air. However, fabricating a high‐quality CsPbBr 3 perovskite film normally requires a high annealing temperature, leading to the difficulty of preparing CsPbBr 3 solar cells with low‐temperature solution process. In this work, we demonstrated a pyridine‐vapor treatment in two‐step fabrication of CsPbBr 3 perovskite films that can reduce the annealing temperature to about 160 °C. The mechanism is attributed to the reaction of pyridine with lead bromide, which forms an intermediate phase and leads to a low activation energy in the formation of CsPbBr 3 perovskite films during thermal annealing. The devices without encapsulation show excellent stability in ambient air with the humidity up to 70%. This work provides a novel approach for preparing inorganic perovskite solar cells at low temperature.