Exciton transport in amorphous polymers and the role of morphology and thermalisation

TL;DR

This paper investigates how morphology and temperature influence exciton transport in amorphous conjugated polymers using a quantum master equation approach, revealing diverse transport regimes and insights into exciton dynamics relevant for organic electronics.

Contribution

It introduces a reduced state quantum master equation model based on Merrifield exciton formalism to study exciton transport in disordered amorphous polymers, highlighting the effects of temperature and disorder.

Findings

Transport regimes vary with thermal energy, electronic couplings, and disorder.

Temperature and disorder significantly affect exciton localization and charge separation.

The model provides insights into non-equilibrium dynamics and thermal equilibrium states of excitons.

Abstract

Understanding the transport mechanism of electronic excitations in conjugated polymers is key to advancing organic optoelectronic applications, such as solar cells, OLEDs and flexible electronics. While crystalline polymers can be studied using solid-state techniques based on lattice periodicity, the characterisation of amorphous polymers is hindered by an intermediate regime of disorder and the associated lack of symmetries. To overcome these hurdles we use a reduced state quantum master equation approach based on the Merrifield exciton formalism. Using this model we study exciton transport in conjugated polymers and its dependence on morphology and temperature. Exciton dynamics consists of a thermalisation process, whose features depend on the relative strength of thermal energy, electronic couplings and disorder, resulting in remarkably different transport regimes. By applying this method to representative systems based on poly(p-phenylene vinylene) (PPV) we obtain insight into the role of temperature and disorder on localisation, charge separation, non-equilibrium dynamics, and experimental accessibility of thermal equilibrium states of excitons in amorphous polymers.