Perovskite-sensitized solar cells were fabricated in the air using sequential deposition technique,for which a key step is spin-coating the solution of PbI2 in N,N-dimethylformamide(DMF)as the precursor for the CH3NH3PbI3 formation on mesoporous TiO2 film.The effect of PbI2 concentration on the optical absorption,electron collection,and photovoltaic performance of the as-prepared devices and the mechanism of charge transfer processes in the devices were herein extensively investigated.