Density of states and energetic correlation in disordered molecular systems due to induced dipoles

Abstract

We have considered two models for a system of disordered organic molecules: one based on a regular lattice with Gaussian site displacements and another based on a hard sphere distribution. The site energies were given by a charge-induced dipole interaction (the polarization energy). We obtained the density of states of both models and observed that it changes from a Gaussian to the density of states of a uniform site distribution, whose form was obtained analytically, depending on the degree of disorder in one model or the packing fraction in the other model. The site energy distribution is short-ranged correlated in both models since nearby molecules polarize basically the same disordered environment.

Hopping charge transport in amorphous semiconductors with the spatially correlated exponential density of states

“…A simple example of such correlation function, though not in the case of the exponential distribution, could be provided by the random energy landscape, generated by randomly oriented dipoles located at the sites of the 1D line 5 or for the disordered material with site energies given by the charge-induced dipole interaction. 39 In addition, we cannot guarantee that even all distributions having non-negative c U (x) may be constructed using the Gaussian A very actual open problem is what kind of correlation functions could be observed in real amorphous materials having the exponential DOS. At the moment we have no reliable information about spatial correlations in inorganic amorphous materials.…”

“…A simple example of such correlation function, though not in the case of the exponential distribution, could be provided by the random energy landscape, generated by randomly oriented dipoles located at the sites of the 1D line 5 or for the disordered material with site energies given by the charge-induced dipole interaction. 39 In addition, we cannot guarantee that even all distributions having non-negative c U (x) may be constructed using the Gaussian Another interesting problem is a more detailed characterization of the various "nondispersive" regimes mentioned earlier. In this paper we used a very simple definition of the nondispersive charge transport as a transport regime where the constant time-independent average carrier velocity eventually develops for the carrier traveling in the infinite medium.…”

Simulations of Morphology and Charge Transport in Supramolecular Organic Materials

“…This approach, initiated by Bässler, has been successfully used by several groups to understand the role of traps, finite charge carrier density, energetic disorder, and other mesoscopic parameters on charge mobility. 8,13,161,[187][188][189][190] At the same time, the necessity of extending the existing discrete mesoscopic models has also become clear: first, the parametrization based on microscopic simulations is not straightforward. 186 Second, either stationary or transient quantities are quantitatively reproduced, while for the description of transient (degradation) processes both should agree with experimental data.…”

Stochastic modeling of molecular charge transport networks

“…Theory and simulations have substantially contributed to our understanding of these processes in amorphous organic semiconductors, in particular (extended, correlated) Gaussian disorder models (GDM) have been successful in rationalizing the influence of finite carrier concentration, Coulomb interactions, the shape of the density of states, spatial correlations of site energy, and positional disorder on transport dynamics. [3][4][5][6][7][8][9][10][11][12] Microscopic approaches, which combine quantum chemistry, charge transfer theories, as well as molecular and statistical mechanics, [13][14][15][16][17][18] are conceptually similar to GDM, except now charge hopping sites are extracted from a large-scale morphology obtained using molecular dynamics and charge transfer rates are determined using first principles calculations. Such a multiscale methodology allows to directly link macroscopic observables to the chemical structure and the morphology and has been used, e.g., to elucidate the influence of stacking motifs in columnar mesophases of liquid crystals 2,[19][20][21] and to study percolating networks and polarization effects in organic crystals.…”