Delocalisation explains efficient transport and charge generation in neat Y6 organic photovoltaics

TL;DR

This study uses advanced simulations to reveal how delocalisation enhances charge transport and generation in neat Y6 organic photovoltaics, explaining their high efficiency without large energetic offsets.

Contribution

The paper introduces a delocalised kinetic Monte Carlo simulation approach to accurately model charge dynamics in Y6, highlighting the role of delocalisation in device efficiency.

Findings

Delocalisation increases carrier mobility and exciton diffusion.

Higher charge-generation efficiencies predicted align with experiments.

dKMC is validated as a predictive tool for OPV performance.

Abstract

Non-fullerene acceptors (NFA), such as Y6, have significantly improved the efficiency of organic photovoltaic devices (OPVs). However, the fundamental processes behind the high efficiencies of NFA devices have remained incompletely understood, with the high efficiencies persisting without the large energetic offsets often thought to be required for charge separation. Even more surprising has been the efficient charge generation in neat Y6 devices, where there is no energetic offset at all. Here, we simulate charge transport and separation in Y6 using delocalised kinetic Monte Carlo (dKMC) parameterised using atomistic calculations, thus taking into account the often-neglected ingredients of delocalisation, disorder, and polaron formation. Including delocalisation predicts higher carrier mobilities and exciton diffusion coefficients than is possible with classical simulations, bringing them into agreement with experimental values. Delocalisation also predicts higher charge-generation efficiencies in neat Y6, in agreement with experimental measurements. Finally, this work establishes dKMC as a realistic, predictive tool for understanding next-generation OPVs.