Ion migration in Br-doped MAPbI3 and its inhibition mechanisms investigated via quantum dynamics simulations

Abstract

MAPb(I_1−xBr_x)₃ is widely used as a window layer in tandem solar cells. Ion migration is one of the most important factors that results in phase separation in MAPb(I_1−xBr_x)₃ and eventually causes a decrease of cell performance. Recent research demonstrates that the doping of Cs⁺ and the formation of low-dimensional perovskite structures are effective means of inhibiting the migration. To investigate the causes of the migration and its inhibition mechanisms in hybrid halide perovskite materials, large-scale quantum dynamics simulations are conducted on MAPbI₃, MAPb(I_0.4Br_0.6)₃ and Cs_0.125MA_0.875Pb(I_0.4Br_0.6)₃, respectively. By tracking changes in the geometric structures of the perovskite materials before and after doping with Br⁻ and Cs⁺ in the dynamics processes, the precondition for the ion migration is firstly revealed. The dimension reduction of the perovskite skeleton structures by introducing Cs⁺ is observed. Furthermore, by combining observations with the variations of the band gap values in all the systems, the inhibition mechanisms of Cs⁺ doping on ion migration in MAPb(I_1−xBr_x)₃ are revealed.