All‐inorganic lead halide perovskites α‐CsPbI₂Br with higher thermal stability and phase stability are promising candidate for optoelectronic application such as photovoltaics. However, the >250 °C high temperature annealing is required to obtain the desired photovoltaic active perovskite phase of α‐CsPbI₂Br, which makes it difficult for fabrication and application based on flexible polymer substrate. Here, a facile formation of high performance all‐inorganic CsPbI₂Br perovskite solar cell is reported, through a one‐step method and a 100–130 °C low temperature annealing process. The facile‐deposited CsPbI₂Br film demonstrates long‐term phase stability at room temperature for a month and exhibits the thermal stability under 100 °C annealing for more than a week. Consequently, the CsPbI₂Br‐based all‐inorganic perovskite solar cells (PSCs) exhibit power conversion efficiencies (PCE) of up to a record value of 10.56%. This low temperature crystallization of all‐inorganic CsPbI₂Br perovskite is a promising approach for scalable, convenient, and inexpensive fabrication in the future.