Despite rapid developments in both photovoltaic and light emitting device performance, the understanding of the optoelectronic properties of hybrid lead halide perovskites is still incomplete. In particular, the polarizability of the material, the presence of molecular dipoles, and their influence on the dynamics of the photo-excitations remains an open issue to be clarified. Here, we investigate the effect of an applied external electric field on the photo-excited species of CH3NH3PbI3 thin films, both at room temperature and at low temperature, by monitoring the photoluminescence (PL) yield and PL decays. At room temperature we find evidence for electric field - induced reduction of radiative bimolecular carrier recombination together with motion of charged defects that affects the non-radiative decay rate of the photo-excited species. At low temperature (190 K), we observe a field - induced enhancement of radiative free carrier recombination rates that lasts even after the removal of the field. We assign this to field induced alignment of the molecular dipoles, which reduces the vibrational freedom of the lattice and the associated local screening, and hence results in a stronger electron - hole interaction.
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