Abstract. The formation of organometal-halide perovskite crystal is simply based on stoichiometry reaction. However, the formation process seems to be sensitively affected by some process parameters such as concentration and temperature of precursor solution. In this work, we studied the formation of CH 3 NH 3 PbI 3 (MAPbI 3 ) crystal in mesoporous TiO 2 layer deposited by spin coating technique. Perovskite layers were characterized by X-Ray Diffraction (XRD) and its surface morphology were investigated by Scanning Electron Microscope (SEM). Perovskite layers obtained from precursor solution at 40°C and 60°C show a mesh-like structure. Meanwhile, for higher precursor solution temperature (80°C), it shows a flake-like structure. However, precursor solution at 60°C produced the best conversion of precursor solution with the smallest percentage of the remaining unconverted PbI 2 inside the produced crystal layer. These experimental results also showed that the best crystallization degree is obtained from 1.0 M precursor solution. The photovoltaic characteristics of their solar cells seem to have a correlation with the quantity of unconverted PbI 2 . High PbI 2 content significantly decreased the Filling Factor of the solar cell.