Exciton Transfer in Organic Photovoltaic Cells: A Role of Local and Nonlocal Electron-Phonon Interactions in a Donor Domain

TL;DR

This study models exciton transfer in organic photovoltaic cells, revealing that nonlocal electron-phonon interactions at high temperatures improve transfer efficiency, while local modes shorten exciton lifetime.

Contribution

It introduces a comprehensive theoretical model incorporating local and nonlocal electron-phonon interactions using HEOM, providing new insights into exciton dynamics in organic photovoltaics.

Findings

Nonlocal interactions enhance exciton transfer at high temperatures.

Local modes reduce exciton lifetime.

Model accurately predicts exciton dynamics under environmental influences.

Abstract

We theoretically investigate an exciton transfer process in a donor domain of organic photovoltaic cells focusing on the roles of local and nonlocal electron-phonon interactions. Our model consists of a three-level system described by the Holstein-Peierls Hamiltonian coupled to multiple heat baths for local and nonlocal molecular modes characterized by Brownian spectral distribution functions. We chose tetracene as a reference donor molecule, where the spectral distribution functions of the local and nonlocal modes exist. We then employ the reduced hierarchy equations of motion (HEOM) approach to simulating the dynamics of the system under the influence of the environment as a function of the electron-phonon coupling strength and temperature. We rigorously calculate the reduced density matrix elements to explain the timescale of dynamics under the influence of the dissipative local and nonlocal modes. The results indicate that the strong nonlocal electron-phonon interaction under high temperature conditions favors the exciton transfer process and enhances the efficiency of organic photovoltaic materials, while the lifetime of the exciton becomes shorter due to a low frequency local mode.