Exciton dissociation mediated by phonons in organic photovoltaics

TL;DR

This paper demonstrates that phonons can overscreen electron-hole attraction in organic photovoltaics, potentially leading to exciton dissociation, which is crucial for improving solar cell efficiency.

Contribution

It introduces a simple lattice model showing phonon-mediated overscreening of electron-hole attraction, highlighting a new mechanism affecting exciton dynamics in organic solar cells.

Findings

Phonons can turn attractive electron-hole interactions into repulsive at short distances.

Phonon-mediated screening influences exciton dissociation in organic materials.

This mechanism may help optimize organic photovoltaic efficiencies.

Abstract

It is well known that phonons can overscreen the bare Coulomb electron-electron repulsion, turning it into the effective attraction that binds the Cooper pairs responsible for BCS superconductivity. Here, we use a simple lattice model to prove that the counterpart of this is also possible, whereby phonons overscreen the bare electron-hole attraction and may turn it repulsive at short distances, driving exciton dissociation in certain regions of the parameter space. We argue that this phonon-mediated short-range screening plays an important role in the physics of organic solar cell materials (and other materials with strong electron-phonon coupling) and could point the way to new strategies for optimizing their efficiencies.