Controlling the crystallization dynamics is one key in optimizing the performance of perovskite solar cells (PSCs). The present study provides a simple approach using a low temperature stable-transition-film (STF) to prepare highly-dense and pinhole-free CsPbIBr2 thin film with high crystalline quality, as well as a new structural design (FTO/NiOx/CsPbIBr2/MoOx/Au) of all-inorganic perovskite solar cells toward long-term thermal stability. For the first time, we demonstrate that MoOx can independently serve as an outstanding cathode buffer layer on an inorganic perovskite layer. The lower work-function MoOx with ultra-thin thickness (4nm) leads to decreases of the Schottky barrier, the contact resistance and the interface trap-state density. This increases the power conversion efficiency (PCE) of all-inorganic planar PSCs from 1.3% to 5.52%. Inspiringly, the FTO/NiOx/CsPbIBr2/MoOx/Au all-inorganic PSCs were demonstrated to possess excellent long-term thermal stability at high temperatures up to 160°C. A simple approach using a low temperature stable-transition-film (STF) to prepare highly-dense and pinhole-free CsPbIBr2 thin film with high bromine content, and a new structural design (FTO/NiOx/CsPbIBr2/MoOx/Au) of MoOx independently buffered all-inorganic perovskite solar cells (PSCs) toward long-term thermal stability. Display omitted •We demonstrated a low-temperature stable-transition-film to prepare uniform CsPbIBr2 thin film.•An ultra-thin MoOx thin film with low work function was realized by post annealing process in nitrogen atmosphere.•MoOx independently served as the cathode buffer layer in all-inorganic perovskite solar cells (FTO/NiOx/CsPbIBr2/MoOx/Au).•The all-inorganic perovskite solar cells were demonstrated to own long-term stability at high temperatures up to 160°C.