Hybrid organic-inorganic lead halide perovskites (HOIPs) have attracted much attention because of their remarkable carrier lifetimes and diffusion lengths. These properties have been attributed to the efficient screening of charge carriers via polaron formation in the highly polar and dynamic environment. Polaron formation explains, at least in part, the moderate charge carrier mobility, but the calculated mobilities are somewhat higher than experimental values. Here we discuss a factor that has been previously overlooked and can potentially account for the discrapency: the effect of dielectric drag. While optical phonon modes of the lead halide sublattice are mainly responsible for polaron formation, slower orientational relaxation of surrounding dipoles adds a dielectric drag to the moving charge. We discuss the role of this dielectric drag based on the measured dielectric function in the gigahertz to terahertz frequency range and how we can understand the unique carrier physics in HOIPs in view of its crystal-liquid duality.
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