Thermodynamic regulation of CH3NH3PbI3 crystal growth and its effect on photovoltaic performance of perovskite solar cells

Abstract

We report a theoretical analysis on the crystallization of CH₃NH₃PbI₃ and the control of grain sizes by varying the two-step reaction temperature from −10 °C to 50 °C based on the present analysis. The thermodynamic equation for CH₃NH₃PbI₃ crystallization is derived by considering the change in Gibbs free energy and the equilibrium concentration of the reaction between the PbI₂ film and CH₃NH₃I solution. The photovoltaic performance of a perovskite solar cell is found to depend on the reaction temperature, which is critical in determining the crystal size of perovskite. The reaction temperature was varied between −10 °C and 50 °C, and the optimal temperature was found to be around 20 °C in our two-step process. The performance enhancement controlled by the grain size with the increase of reaction temperature could be compensated by the generation of defects for a large crystal perovskite layer device.