Delocalised kinetic Monte Carlo for simulating delocalisation-enhanced charge and exciton transport in disordered materials

TL;DR

This paper introduces a three-dimensional delocalised kinetic Monte Carlo model to accurately simulate charge and exciton transport in moderately disordered materials, revealing the importance of wavefunction delocalisation for mobility enhancement.

Contribution

It presents the first 3D model of delocalised charge transport in intermediate disorder regimes, integrating quantum effects into kinetic Monte Carlo simulations.

Findings

Standard kinetic Monte Carlo underestimates mobilities in disordered semiconductors.

Partial delocalisation significantly enhances charge mobility.

3D calculations capture important delocalisation effects missed by lower-dimensional models.

Abstract

Charge transport is well understood in both highly ordered materials (band conduction) or highly disordered ones (hopping conduction). In moderately disordered materials -- including many organic semiconductors -- the approximations valid in either extreme break down, making it difficult to accurately model the conduction. In particular, describing wavefunction delocalisation requires a quantum treatment, which is difficult in disordered materials that lack periodicity. Here, we present the first three-dimensional model of partially delocalised charge and exciton transport in materials in the intermediate disorder regime. Our approach is based on polaron-transformed Redfield theory, but overcomes several computational roadblocks by mapping the quantum-mechanical techniques onto kinetic Monte Carlo. Our theory, delocalised kinetic Monte Carlo (dKMC), shows that the fundamental physics of transport in moderately disordered materials is that of charges hopping between partially delocalised electronic states. Our results reveal why standard kinetic Monte Carlo can dramatically underestimate mobilities even in disordered organic semiconductors, where even a little delocalisation can substantially enhance mobilities, as well as showing that three-dimensional calculations capture important delocalisation effects neglected in lower-dimensional approximations.