Origin of intra- and interlayer excitons in a two-dimensional halide perovskite

Two-dimensional halide perovskites are organic-inorganic materials with robust stability whose photophysics are governed by quantum and dielectric confinement, resulting in highly tunable excitonic properties. The absorption and photoluminescence spectra of these materials display several distinct features whose origin is the subject of ongoing debate.

We studied the excitonic fine structure of (PEA)$_2$PbI$_4$ using first-principles $GW$ and Bethe-Salpeter Equation and density functional perturbation theory calculations. Our findings indicate that electrostatic asymmetry in the unit cell results in split excitonic absorption peaks. Additionally, our calculations predict the direction of excitonic transition dipole moments, the presence of interlayer excitons, and demonstrate the importance of exciton-phonon interactions in these materials. These results allow us to explain the complex fine structure of experimentally observed low-temperature polarized photoluminescence results and open the door for deliberate manipulation of intra- and interlayer excitons in low-dimensional perovskites.