Optical conductivity and optical effective mass in a high-mobility organic semiconductor: Implications for the nature of charge transport

TL;DR

This study uses multiscale modeling to analyze the infrared optical properties of rubrene, revealing that light carriers do not necessarily indicate band-like transport, with implications for understanding charge mobility.

Contribution

It demonstrates how nonlocal electron-phonon interactions and thermal disorder influence optical effective masses and charge transport in high-mobility organic semiconductors.

Findings

Nonlocal electron-phonon interactions can reduce optical effective masses.

Localized carriers dominate charge transport at room temperature.

Light carriers do not always imply band-like transport.

Abstract

We present a multiscale modeling of the infrared optical properties of the rubrene crystal. The results are in very good agreement with the experimental data that point to nonmonotonic features in the optical conductivity spectrum and small optical effective masses. We find that, in the static-disorder approximation, the nonlocal electron-phonon interactions stemming from low-frequency lattice vibrations can decrease the optical effective masses and lead to lighter quasiparticles. On the other hand, the charge-transport and infrared optical properties of the rubrene crystal at room temperature are demonstrated to be governed by localized carriers driven by inherent thermal disorders. Our findings underline that the presence of apparently light carriers in high-mobility organic semiconductors does not necessarily imply band-like transport.