| With the rapid increase in human demand for energy,perovskite solar cells are considered to be one of the most promising solar cells for replacing traditional silicon solar cells due to their low manufacturing cost and high photoelectric conversion efficiency.In the mixed halide perovskite material,MAPb(I1-xBrx)3(MA=CH3NH3,O(?)x(?)1)can change the band gap between 1.6 and 2.3eV by adjusting the ratio of halogen atoms.There is a good application prospect in laminated solar cells.The phase separation caused by ion migration causes the device efficiency based on the solar cell material to be unstable,thereby limiting the practical application of the mixed halide perovskite.At present,the research on the mechanism of ion migration phenomenon is still lacking,so the research to improve the ion migration phenomenon and improve the material stability has been hindered.In this paper,ab initio quantum dynamics method is used to simulate the long-term MAPbI3 system doped with X and A sites,and the ion migration paths of different doped systems at 300 and 450 K temperatures are observed.The ion distribution,band gap,and structure are compared and analyzed before and after.The mechanism of different types of ion migration in different systems is systematically studied.The theoretical calculation data is in good agreement with existing experimental results.In this work,by analyzing the changes of the geometry of the system before and after Pb-X doping,we first revealed that in the process of dynamics,the interaction between polar and stick MA+groups and Pb-X framework resulted in the fracture of Pb-X bond,which is the premise of the occurrence of ion migration;with the increase of temperature,the interaction between M A+groups and Pb-X framework is intensified,and the introduction of Br-aggravates the distortion of MAPbI3 lattice,thus increasing the fracture of Pb-X proportion,halogen in the dynamic process by moving between different Pb2+ similar to monkey in the way of moving between trees.Then,by studying the effect of Cs+ on the dimensionality reduction of the perovskite structure in the dynamics process,and combining the band gap change law of the system,the inhibition mechanism is proposed.The introduction of Cs+ with weak polarity and small ion radius leads to Cs0.125MA0.875Pb(I0.4Br0.6)3 lattice structure evolved from the initial 3D to 2D/3D mixed dimensions.This evolution,on the one hand,reduced the number of dangling bonds in the system and reduced the mechanism of the probability of ion migration.In addition,due to the The quantum confinement effect of the low-dimensional structure widens the band gap of the system.As a window layer material,the increased band gap has a positive contribution to improve the efficiency of the laminated battery.By comparing the temperature,it is found that temperature promotes migration and may cause the inhibitory effect of Cs+ at normal temperature to disappear,that is,temperature is a problem that cannot be ignored on the road to solve ion migration.The work of this paper has a systematic and in-depth understanding of the mechanism of ion migration through the dynamic simulation of atomic and molecular levels.It is intended to provide important theoretical guidance for improving ion migration and improving the stability and photovoltaic performance of mixed perovskite materials. |
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