All inorganic CsPbI₃ perovskite solar cells (PSCs) have emerged as disruptive photovoltaic technology owing to their admirable photoelectric properties and the non-volatile active layer. However, the phase instability against moisture severely limits the fabrication environment for the high-efficiency devices, breaking through the confinement region to achieve scalable manufacturing has been the primary issue for future commercialization. Here, we develop a curing-anti-solvent strategy for fabricating high-quality and stable black-phase CsPbI₃ perovskite films in ambient air by introducing an inorganic polymer perhydropolysilazane (PHPS) into methyl acetate to form anti-template agent. The cross-linked PHPS reduces moisture erosions while the hydrolyzate silanol network (–Si(OH)₄–) controls the perovskite crystal growth by forming Lewis adducts with PbI₂ during the fabrication. The polycondensation adduct of Si–O–Si/Si–O–Pb strongly binds to CsPbI₃ grains as a shield layer to hamper phase transition. Using the inorganic CsPbI₃ perovskite thin-film with PHPS-modified anti-solvent processing as the light absorber, the n–i–p planar solar cell achieved an efficiency of 19.17% under standard illumination test conditions. More importantly, the devices showed excellent moisture stability, retaining about 90% of the initial efficiency after 1000 h under 30% RH.