Density of states in locally ordered amorphous organic semiconductors: emergence of the exponential tails

TL;DR

This paper introduces a simple model showing how local order in amorphous organic semiconductors naturally leads to exponential tails in the density of states, driven mainly by electrostatic effects from dipoles or quadrupoles.

Contribution

It demonstrates that local ordering and electrostatic interactions can produce exponential DOS tails, a common feature in amorphous organic semiconductors, with minimal dependence on microstructure details.

Findings

Exponential DOS tails arise from local order and electrostatics.

Orientation preferences of dipoles or quadrupoles influence tail formation.

The mechanism is robust across different microstructures.

Abstract

We present a simple model of the local order in amorphous organic semiconductors which naturally produces a spatially correlated exponential density of states (DOS). The dominant contribution to the random energy landscape is provided by electrostatic contributions from dipoles or quadrupoles. An assumption of the preferable parallel orientation of neighbor quadrupoles or antiparallel orientation of dipoles directly leads to the formation of the exponential tails of the DOS even for a moderate size of the ordered domains. The insensitivity of the exponential tail formation to the details of the microstructure of the material suggests that this mechanism is rather common in amorphous organic semiconductors.