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The extended carrier lifetime in hybrid halide perovskites was attributed toa quasi-indirect band gap that arises due to Rashba splitting in bothconduction and valence band edges. In this paper, we present results for aneffective relativistic band structure of (CH3NH3)PbI3 with the focus on thedispersion of electronic states near the band edges of (CH3NH3)PbI3 affected bythermal structural fluctuations. We establish a relation between the magnitudeof Rashba splitting and a deviation of Pb-atom from its centrosymmetric siteposition in the PbI6 octahedron. For the splitting energy to reach the thermalenergy kT~26 meV (room temperature), the displacement should be of the order0.3 Ang, which is far above the static displacements of Pb-atoms in thetetragonal phase of (CH3NH3)PbI3. The significant dynamic enhancement of theRashba splitting observed at earlier simulation times (less than 2 ps) laterweakens and becomes less than the thermal energy despite the averagedisplacement of Pb-atoms remaining large (0.37 Ang). It is randomization ofPb-displacement vectors and associated cancelation of the net effectivemagnetic field acting on electrons at the conduction band edge is responsiblefor reduction of the Rashba splitting. The lattice dynamics also leads todeterioration of Bloch character for states in the valence band leading tosubsequent localization of holes, which affects bipolar mobility of chargecarriers in (CH3NH3)PbI3. These results call into question the quasi-indirectband gap as a reason for the long carrier lifetime observed in (CH3NH3)PbI3 atroom temperature. An alternative mechanism involves dynamic localization ofholes and their reduced overlap with electrons in reciprocal space.

Structural dynamics in hybrid halide perovskites: Bulk Rashba splitting, spin texture, and carrier localization