Intermediate Polaronic Charge Transport in Organic Crystals from a Many-Body First-Principles Approach

TL;DR

This paper introduces a many-body first-principles method to accurately predict charge carrier mobility in organic molecular crystals within the intermediate electron-phonon coupling regime, bridging the gap between band and hopping transport models.

Contribution

It develops a parameter-free approach combining a finite-temperature cumulant method with Green-Kubo calculations to model intermediate polaronic charge transport in organic crystals.

Findings

Predicted electron mobility within a factor of 1.5-2 of experimental values between 100-300 K.

Revealed strong coupling of electrons with both inter- and intramolecular phonons in the intermediate regime.

Identified formation of broad polaron satellite peaks and limitations of Boltzmann transport theory.

Abstract

Predicting the electrical properties of organic molecular crystals (OMCs) is challenging due to their complex crystal structures and electron-phonon (e-ph) interactions. Charge transport in OMCs is conventionally categorized into two limiting regimes $-$ band transport, characterized by weak e-ph interactions, and charge hopping due to localized polarons formed by strong e-ph interactions. However, between these two limiting cases there is a less well understood intermediate regime where polarons are present but transport does not occur via hopping. Here we show a many-body first-principles approach that can accurately predict the carrier mobility in OMCs in the intermediate regime and shed light on its microscopic origin. Our approach combines a finite-temperature cumulant method to describe strong e-ph interactions with Green-Kubo transport calculations. We apply this parameter-free framework to naphthalene crystal, demonstrating electron mobility predictions within a factor of 1.5$-$2 of experiment between 100$-$300 K. Our analysis reveals that electrons couple strongly with both inter- and intramolecular phonons in the intermediate regime, as evidenced by the formation of a broad polaron satellite peak in the electron spectral function and the failure of the Boltzmann equation. Our study advances quantitative modeling of charge transport in complex organic crystals.