Temperature-dependent structural fluctuation and its effect on the electronic structure and charge transport in...

The recently discovered hybrid organic-inorganic perovskites have been suggested for high-performance optoelectronic applications. Owing to the mechanical flexibility of these compounds, they demonstrate structural fluctuation at finite temperatures that have been widely discussed with respect to their optical properties. However, the effect of temperature-induced structural fluctuation is not clear until now, with respect to the equally important charge transport properties. In the present study, through ab initio molecular dynamics simulations of cubic-phase CH₃ NH₃ PbI₃ at different temperatures, the temperature-dependent electronic structure and charge carrier transport properties are examined. Compared with the significant structural fluctuation of organic cations, the structural change of the inorganic framework is minor. In addition, because the band edge states at R point are mainly influenced by the anti-bonding character of the Pb-I bond, CH₃ NH₃ PbI₃ demonstrates relatively small deformation potentials as well as low temperature dependence of band gaps (ΔE_g  ≈ 50 meV from 330 K to 400 K) and electron-phonon coupling strengths, despite the large structural fluctuation of organic cations. Furthermore, the effective mass of the valence band increases with the increase of temperature. The predicted mobilities of CH₃ NH₃ PbI₃ can reach above 75 cm² V^-1  s^-1 near room temperature, exhibiting an appropriate optoelectronic potential, while the temperature dependence is steeper than T^-1.5 of the traditional semiconductors because of the enhanced effective masses.