Tunable Frohlich Polarons in Organic Single-Crystal Transistors

TL;DR

This paper investigates how the dielectric environment influences charge transport in organic single-crystal transistors, revealing a transition from metallic to insulating behavior explained by a Frohlich polaron model.

Contribution

It demonstrates that the dielectric constant of the insulator controls the polaronic coupling regime, providing a quantitative model for the observed transport behavior.

Findings

Mobility shifts from metallic-like to insulating-like with higher dielectric constant.

Frohlich polaron model accurately describes the transport crossover.

Increasing dielectric polarizability induces a transition from weak to strong polaronic coupling.

Abstract

In organic field effect transistors (FETs), charges move near the surface of an organic semiconductor, at the interface with a dielectric. In the past, the nature of the microscopic motion of charge carriers -that determines the device performance- has been related to the quality of the organic semiconductor. Recently, it has been appreciated that also the nearby dielectric has an unexpectedly strong influence. The mechanisms responsible for this influence are not understood. To investigate these mechanisms we have studied transport through organic single crystal FETs with different gate insulators. We find that the temperature dependence of the mobility evolves from metallic-like to insulating-like with increasing the dielectric constant of the insulator. The phenomenon is accounted for by a two-dimensional Frohlich polaron model that quantitatively describes our observations and shows that increasing the dielectric polarizability results in a crossover from the weak to the strong polaronic coupling regime.