Investigation of carrier transport behavior for cubic CH₃NH₃SnX₃ and CH₃NH₃PbX₃ (X=Br and I) using Boltzmann transport equation

As a novel semiconductor, hybrid halide perovskites become candidate materials for the next generation of solar cells due to their high conversion efficiency and low processing cost. In the face of the uncertainty of electric transport properties in experimental measurement, it is necessary to predict the upper limit of mobility that they theoretically achieve. In this work, a new approach is adopted to improve the computational efficiency. Phonon-limited mobility for CH₃NH₃SnX₃ and CH₃NH₃PbX₃ (X=Br and I) is successfully predicted by ab initio Boltzmann transport equation (BTE) including all electron–phonon interactions (EPI). The convergent values for high frequency dielectric constant and Born effective charge are first obtained with moderate k grids of 16×16×16, and then they are substituted into the program. Subsequently, EPI matrix element is obtained by density functional perturbation theory (DFPT) with coarse 4×4×4 k/q grids. To correct the shape of the band edge, the spin–orbit coupling (SOC) effect is included in the calculation. We reveal that longitudinal optical (LO) phonons associated with the stretching of Pb(Sn)-I(Br) atoms limit carrier mobility. CH₃NH₃SnI₃ exhibits higher mobility than other materials. Its drift mobility is as high as μ_e=403∼559 and μ_h=1558∼1734cm²V⁻¹s⁻¹. Furthermore, Hall factor is investigated by analyzing the average relaxation time, and Hall mobility is predicted to be μ_e=432∼598 and μ_h=1725∼1920cm²V⁻¹s⁻¹. Compared with other typical semiconductors, CH₃NH₃SnI₃ exhibits high hole mobility.