Hopping charge transport in organic materials

TL;DR

This paper explores how electrostatic disorder, caused by dipoles and quadrupoles, influences charge transport in disordered organic materials, affecting mobility, current transients, and charge injection near electrodes.

Contribution

It provides a detailed analysis of electrostatic disorder's role and its spatial correlation, including effects near electrodes and inter-charge interactions, which are novel insights.

Findings

Electrostatic disorder dominates energetic disorder in organic materials.

Spatial correlation of disorder governs field-dependent mobility.

Electrode proximity modifies electrostatic disorder and charge injection characteristics.

Abstract

General properties of the transport of charge carriers (electrons and holes) in disordered organic materials are discussed. It was demonstrated that the dominant part of the total energetic disorder in organic material is usually provided by the electrostatic disorder, generated by randomly located and oriented dipoles and quadrupoles. For this reason this disorder is strongly spatially correlated. Spatial correlation directly governs the field dependence of the carrier drift mobility. Shape of the current transients, which is of primary importance for a correct determination of the carrier mobility, is considered. A notable feature of the electrostatic disorder is its modification in the vicinity of the electrode, and this modification takes place without modification of the structure of the material. It is shown how this phenomenon affects characteristics of the charge injection. We consider also effect of inter-charge interaction on charge transport.