The Enhancement of Interfacial Exciton Dissociation by Energetic Disorder is a Nonequilibrium Effect

TL;DR

This paper shows that moderate energetic disorder in molecular systems can enhance exciton dissociation in photovoltaic materials through a nonequilibrium process involving long-lived intermediate states.

Contribution

It introduces a kinetic model demonstrating how energetic disorder promotes charge separation via nonequilibrium effects and long-lived intermediate states.

Findings

Moderate energetic disorder increases charge dissociation yields.

Nonequilibrium effects facilitate formation of long-lived intermediate states.

The kinetic model reproduces experimental-like behavior with appropriate parameters.

Abstract

The dissociation of excited electron-hole pairs is a microscopic process that is fundamental to the performance of photovoltaic systems. For this process to be successful, the oppositely charged electron and hole must overcome an electrostatic binding energy before they undergo ground state recombination. Here we use a simple model of charge dynamics to investigate the role of molecular disorder in this process. This model reveals that moderate spatial variations in electronic energy levels, such as those that arise in disordered molecular systems, can actually increase charge dissociation yields. We demonstrate that this is a nonequilibrium effect that is mediated by the dissipation driven formation of partially dissociated intermediate states that are long-lived because they cannot easily recombine. We present a kinetic model that incorporates these states and show that it is capable of reproducing similar behavior when it is parameterized with nonequilibrium rates.