Temperature and Field Dependence of the Mobility in Liquid-Crystalline Conjugated Polymer Films

TL;DR

This study investigates how temperature and electric field influence charge mobility in liquid-crystalline conjugated polymer films, revealing weak dependence due to spatial order and disorder effects through Monte Carlo simulations.

Contribution

It provides a detailed simulation-based analysis of charge transport in ordered conjugated polymer films, highlighting the effects of thermal energy and disorder on mobility.

Findings

Mobility shows weak dependence on electric field and temperature in ordered films.

Thermal energy comparable to energetic disorder explains the weak dependence.

Spatial disorder reduces the absolute value of mobility without changing qualitative behavior.

Abstract

The transport properties of organic light-emitting diodes in which the emissive layer is composed of conjugated polymers in the liquid-crystalline phase have been investigated. We have performed simulations of the current transient response to an illumination pulse via the Monte Carlo approach, and from the transit times we have extracted the mobility of the charge carriers as a function of both the electric field and the temperature. The transport properties of such films are different from their disordered counterparts, with charge carrier mobilities exhibiting only a weak dependence on both the electric field and temperature. We show that for spatially ordered polymer films, this weak dependence arises for thermal energy being comparable to the energetic disorder, due to the combined effect of the electrostatic and thermal energies. The inclusion of spatial disorder, on the other hand, does not alter the qualitative behaviour of the mobility, but results in decreasing its absolute value.