Theoretical Study On The Effect Of Doping For The Stability Of Perovskite Solar Cell Materials

In the past few years,the remarkable energy conversion efficiency of lead-halide-based perovskite solar cells?PSCs?has drawn extraordinary attention.However,some exposed problems in PSCs such as the low chemical stability and so forth are tough to eliminate.Ion migration will cause the anomalous hysteresis in the current-voltage?I-V?curves of CH₃NH₃PbI₃,which is also a major cause of low stability.Therefore,finding a method that hinders the main diffusers'migration can improve the stability of the cells,and is of great significance for designing a high-performance perovskite solar cells.In this study,bromine and cerium ions are selected to replace iodine and methyl ammonium cations,respectively,and the corresponding diffusion barriers of halogen vacancies and interstitial ions are calculated.Density functional theory is used to study the photoelectric properties of the substituted perovskites et al.The main contents of this thesis are given below:?1?The iodide ions in the CH₃NH₃PbI₃ perovskite are replaced with bromide ions by 50%and 100%respectively,and vacancy and interstitial ion defects are designed for halide ions respectively.The halide ions'diffusion barriers of the three kinds of CH₃NH₃PbI₃,CH₃NH₃PbBr₃ and CH₃NH₃Pb(I_0.5Br_0.5)₃ are calculated.The results show that bromine substitution can effectively increase the migration barrier of halogen ions,thereby inhibiting the migration of halogen ions.?2?The band structures and light absorption coefficients of the three perovskites after bromine replacement are calculated,and the results show that the band gaps of CH₃NH₃Pb(I_0.5Br_0.5)₃ and CH₃NH₃PbBr₃ are higher than that of CH₃NH₃PbI₃,and the light absorption performance of the two perovskites are inferior to that of CH₃NH₃PbI₃to varying degrees.This shows that the iodide ion should be partially replaced with bromine instead of fully replaced.?3?Half and complete replacement of methyl ammonium cations in CH₃NH₃PbI₃with cesium ions.The results show that the band structures and bandgap values of the three perovskites are very similar,and the light absorption capacity are also basically the same.Although the full replacement with cesium can not effectively increase the diffusion barrier of iodide ions,the half replacement with cesium can significantly increase the migration barrier of iodide ions,thereby inhibiting the migration of iodide ions.