Large Polaron Formation and its Effect on Electron Transport in Hybrid Perovskite

Many experiments have indicated that large polaron may be formed in hybrid perovskite, and its existence is proposed to screen the carrier-carrier and carrier-defect scattering. However, detailed theoretical study of the large polaron and its effect on carrier transport at the atomic level is still lacking. In this work, using CH₃NH₃PbI₃ as an example, we implement tight-binding model fitted from the density-functional theory to describe the electron large polaron ground state and to understand the large polaron formation and transport at its strong-coupling limit. We find that the formation energy of the large polaron is around -12 meV for the case without dynamic disorder, and -55 meV by including dynamic disorder. By performing the explicit time-dependent wavefunction evolution, together with the rotations of CH₃NH₃⁺ and vibrations of PbI₃^- sublattice, we studied the diffusion constant and mobility of the large polaron state. On one hand, the vibration of the sublattice provides additional driving force for carrier mobility, on the other hand, the large polaron polarization further localizes the electron, reducing its mobility.