Charge Stripe Formation in Molecular Ferroelectric Organohalide Perovskites for Efficient Charge Separation

Despite rapid progress in the efficiency of organohalide perovskite based solar cells, physical mechanisms underlying their efficient charge separation and slow charge recombination still elude us. Here we provide direct evidence of spontaneous charge separation via first-principles simulations. The excitons are predicted to self-organize into stripes of photoexcited electrons and holes, spatially separated as effective channels for charge transport. The rotation of organic cations deforms the inorganic framework, and as the deformation reaches a critical value, a direct band gap transforms to an indirect one, and the photoexcited electrons rotate in alignment with the deformation-induced electric fields. The latter triggers a Stark effect which in turn leads to the formation of charge stripes. The interplay between dynamic disorder, ionic bonding, and polarization is responsible for the formation of the charge stripes and the indirect band gap, both of which could lead to efficient charge separation and reduced charge recombination in the organohalide perovskites.