Exciton energy disorder in polar amorphous organic thin films: Monte Carlo calculations

We report on Monte Carlo calculations of the exciton energy level disorder in polar amorphous organic solids arising from electrostatic interactions between polarizable molecular charge distributions. In contrast to previous reports in which the discrete molecular polarizabilities are modeled as a dielectric continuum having dielectric constant $ϵ$, our calculations take account of the molecular-scale polarization inhomogeneity. We demonstrate that exciton energy level disorder is only weakly dependent on $ϵ$. For a range of $ϵ$ typical of organic solids, we report an empirical expression for the energy level disorder, and show that conventional dielectric continuum models are not consistent with the observed results. Results of our calculations are shown to be consistent with experimental measurements of exciton energy disorder in aluminum tris-(8-hydroxyquinoline).