Exciton splitting in 2D layered metal-halide perovskites

Abstract

Abstract Layered 2D perovskites are making inroads as materials for photovoltaics and light emitting diodes, but the photophysics of their optical excitations is still debated. Although their large exciton binding energies should hinder charge separation, significant evidence has been uncovered for an abundance of free carriers. Several explanations have been proposed, like exciton splitting at grain boundaries or polaron formation, without clarifying yet if excitons form and then split, or if the formation is prevented by competing relaxation processes. Here we address exciton stability in layered PEA2PbI4 in n = 1 Ruddlesden-Popper phase, both in form of thin film and single crystal. Samples are resonantly excited to directly inject cold excitons, whose dissociation is then demonstrated with femtosecond differential transmission. The results presented here establish the intrinsic nature of exciton dissociation in 2D Ruddlesden-Popper layered perovskites, demonstrating that they are free carrier semiconductors like their 3D counterparts, belonging to a universal photophysical framework.