Perovskite crystallizations under different temperature phases have tremendously effects on the performance of perovskite solar cells. Here, we report an effective near-room-temperature fabrication technique to prepare high quality organolead halide perovskite films. By doping a certain amount of cesium cations into precursor solution, smooth and well-crystallized perovskite films with no other impurity phase can be obtained at an annealing temperature of 50 degrees C. This phenomenon can be interpreted as relatively low energy required for the diffusion of cesium cations into intermediate phase framework, promoting the removal of DMSO and subsequent diffusion of organic cations. Corresponding PSCs has been prepared based on this technique, and the highest PCE of 17.9% has been obtained with annealing temperature of only 50 degrees C. This work exhibits a well balance between reducing of annealing temperature and increase of device performance and is expected to broaden the range of choices for substrate materials.