Cesium-based fully inorganic black-phase (BP) lead halide perovskites (such as alpha-, beta-, and gamma-CsPbI3) with excellent thermal stability and a decently high photovoltaic performance have attracted increasing attention. However, a below 200 degrees C fabrication process of the desirable BP CsPbI3 has rarely been reported. Herein, the detailed crystal structure evolution of ambient-air-stable BP CsPbI3 prepared under low temperature conditions is investigated by exploiting the strong coordination bonding between C(sic)O in polyvinylpyrrolidone (PVP) and Pb in CsPbI3 and inflection effect of PVP under annealing. It is found that ambient-air-stable BP CsPbI3 films are formed and the energy barrier for the long-term stable BP CsPbI3 formation is significantly reduced (the required annealing temperature is only 80 degrees C). After optimization, the highest power conversion efficiencies (PCEs) of approximate to 4.0% and 10.0% are recorded for the 3% PVP-added devices with light absorbers annealed at 80 and 160 degrees C, respectively. More importantly, the 3% PVP device annealed at 160 degrees C maintains approximate to 80% of its original PCE after 5 months storage under ambient-air conditions.