Exciton in Halide Perovskite Nanoplatelets: Finite Confinement and Dielectric Effect in Effective Mass Approximation

Abstract

In recent years, there has been a surge of interest in two-dimensional (2D) lead halide perovskites (LHPs) due to their high potential for optoelectronic devices. There is experimental evidence that carriers and excitons are not totally confined in these atomically thin 2D crystals, surrounded by organic ligands. Taking into account previous results on density functional theory calculations, we use the variational method and k.p approach to solve the Hamiltonian of excitons in nanoplatelets (NPLs) including quantum and dielectric confinements, surface stress, Coulomb interaction, and finite barrier potential. Essential characteristics such as exciton energy, binding energy, and reduced mass are discussed in two inorganic LHPs, CsPbBr₃ and CsPbI₃, as model systems. For NPL thickness comparable to or smaller than the Bohr exciton radius, a good agreement between theory and experiment is obtained for the exciton energy. This agreement is achieved through consideration of the band offset between the NPL and surrounding ligands, coupled to a carrier mass thickness dependence, showing that previous studies which consider an infinite confinement largely overestimate the exciton energy of thin NPLs. The dielectric environment of the NPL emerges as a pivotal parameter influencing the exciton binding energy.