Far tails of the density of states in amorphous organic semiconductors

TL;DR

This paper calculates the far tails of the density of states in amorphous organic semiconductors using dipolar and quadrupolar glass models, revealing non-Gaussian, asymmetric features that impact charge transport at low temperatures.

Contribution

It introduces detailed models of the far tails of the DOS in amorphous organic semiconductors, highlighting non-Gaussian and asymmetric characteristics related to dipolar and quadrupolar interactions.

Findings

Far tails are non-Gaussian in both models.

DOS symmetry differs between dipolar and quadrupolar glasses.

Asymmetry affects charge transport and mobility at low temperatures.

Abstract

Far tails of the density of state (DOS) are calculated for the simple models of organic amorphous material, the model of dipolar glass and model of quadrupolar glass. It was found that in both models far tails are non-Gaussian. In the dipolar glass model the DOS is symmetric around zero energy, while for the model of quadrupolar glass the DOS is generally asymmetric and its asymmetry is directly related to the particular geometry of quadrupoles. Far tails of the DOS are relevant for the quasi-equilibrium transport of the charge carriers at low temperature. Asymmetry of DOS in quadrupolar glasses means a principal inequivalence of the random energy landscape for the transport of electrons and holes. Possible effect of the non-Gaussian shape of the far tails of the DOS on the temperature dependence of carrier drift mobility is discussed.