Ferroelectric Domains May Lead to Two-Dimensional Confinement of Holes, but not of Electrons, in CH3NH3PbI3 Perovskite

We investigate the possibility that formation of ferroelectric domains in CH3NH3PbI3 can separate the diffusion pathways of electrons and holes. This hypothesis has been proposed to explain the large recombination time and the remarkable performance of solar cells of hybrid perovskites. We find that a two-dimensional hole confinement in CH3NH3PbI3 is possible under room-temperature conditions. Our models of the tetragonal phase show that the alignment of dipole layers of organic cations induces the confinement of holes but not of electrons. This behavior does not change even when the strength of the ordered dipoles is varied. The confinement of holes is favored by asymmetric deformation of the inorganic framework triggered by its interaction with the organic cations. However, the lattice distortions counteract the effect of the oriented organic dipoles, preventing the localization of electrons.