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

MAPb(I1-xBrx)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(I1-xBrx)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(I0.4Br0.6)3 and Cs0.125MA0.875Pb(I0.4Br0.6)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(I1-xBrx)3 are revealed.