Excitonic and Polaronic Properties of 2D Hybrid Organic–Inorganic Perovskites

We theoretically characterize the unusual white-light emission properties of two-dimensional (2D) hybrid organic–inorganic perovskites with an APbX4 structure (where A is a bidentate organic cation and X = Cl, Br). In addition to band structure calculations including corrections due to spin–orbit couplings and electron–hole interactions, a computationally intensive molecular cluster approach is exploited to describe the excitonic and polaronic properties of these 2D perovskites at the atomistic level. Upon adding or removing an electron from the neutral systems, we find that strongly localized small polarons form in the 2D clusters. The polaron charge density is distributed over just ∼1.5 lattice sites, which is consistent with the calculated large polaron binding energies, on the order of ∼0.4–1.2 eV.