One-photon absorption by inorganic perovskite nanocrystals: A theoretical study
arXiv:2004.05093 · doi:10.1103/PhysRevB.101.195414
Abstract
The one-photon absorption cross section of nanocrystals (NCs) of the inorganic perovskite CsPbBr is studied theoretically using a multiband envelope-function model combined with a treatment of intercarrier correlation by many-body perturbation theory. A confined exciton is described first within the Hartree-Fock (HF) approximation, and correlation between the electron and hole is then included in leading order by computing the first-order vertex correction to the electron-photon interaction. The vertex correction is found to give an enhancement of the near-threshold absorption cross section by a factor of up to 4 relative to the HF (mean-field) value of the cross section, for NCs with an edge length -12 nm (regime of intermediate confinement). The vertex-correction enhancement factors are found to decrease with increasing exciton energy; the absorption cross section for photons of energy eV (about 0.7 eV above threshold) is enhanced by a factor of only 1.4-1.5 relative to the HF value. The corrections to the absorption cross section are also significant; they are found to increase the cross section at an energy eV by about 30% relative to the value found in the effective-mass approximation. The theoretical absorption cross section at eV, assuming a Kane parameter eV, is found to be intermediate among the set of measured values (which vary among themselves by nearly an order of magnitude) and to obey a power-law dependence on the NC edge length , in good agreement with experiment. The dominant contribution to the theoretical exponent 2.9 is shown to be the density of final-state excitons. The main theoretical uncertainty in these calculations is in the value of the Kane parameter .
15 pages, 8 figures