Nucleation mechanism of CH3NH3PbI3 with two-step method for rational design of high performance perovskite solar cells

The performance of Organic-inorganic hybrid perovskite solar cells strongly depend on the quality of perovskite layer. Features of perovskite layer such as grain size, shape, orientation and coverage are mainly determined by the earlier stages of nucleation and growth, which can be controlled by the deposition conditions. Thus, detailed knowledge of such correlations is helpful to optimize thin film quality with regard to controll the deposition parameters. In this work, based on AFM and SEM studies, we find that priority nucleation sites of CH3NH3PbI3 are located at PbI2 grain boundaries and defects. According to the kinetics of heterogeneous nucleation, PbI2 grain boundaries and defects shape factor are more effective than solid surface, where the nucleus formed easily. Inhibiting nucleation rate and promoting grown up factor can contribute to growing up larger size crystals. Through the optimization of the two step deposition method, we get the best cell efficiency of 17.80%.