Stability and phonon-limited mobility for CsSnI3 and CsPbI3

Phase stability of CsSnI3 and CsPbI3 is revealed by analyzing molecular volume, free energy and lattice vibration. Furthermore, the carrier effective mass is calculated by constant energy surface. Surprisingly, the values for electron/hole are as low as 0.06/0.03 m0 for B-α CsSnI3, and 0.08/0.06 m0 for B-α CsPbI3. They gradually increase in the order of B-α, B-β and B-γ. The effective mass for CsSnI3 is lower than that for CsPbI3, implying a high mobility in CsSnI3. At 300 K, the mobility is predicted by empirical models and electron-phonon coupling (EPC) matrix element based on Boltzmann transport equation (BTE). The value from longitudinal acoustic phonon (LAP) model is much higher than that from longitudinal optical phonon (LOP) model. So the mobility is mainly determined by the scattering from polar optical phonon. These perovskites exhibit small high frequency dielectric constant (ϵ∞) and large dielectric constant difference (Δϵ = ϵ0 − ϵ∞), which limit the mobility. Finally, phonon-limited mobility is predicted by the EPC matrix element. The values of CsSnI3/CsPbI3 are μe = 311/118 and μh = 450/70 cm2V−1s−1 in B-β, μe = 99/70 and μh = 218/46 cm2V−1s−1in B-γ.