Band-like motion and mobility saturation in organic molecular semiconductors

TL;DR

This paper explains the unusual charge mobility in organic semiconductors as a combination of band-like carriers and dynamically localized incoherent states caused by thermal lattice fluctuations.

Contribution

It introduces a model that captures the coexistence of band carriers and incoherent localized states due to thermal disorder in organic semiconductors.

Findings

Charge mobility shows metallic-like power-law behavior.

Thermal lattice fluctuations cause dynamic localization of carriers.

Mobility saturation occurs despite low mean-free-paths.

Abstract

We analyze a model that accounts for the inherently large thermal lattice fluctuations associated to the weak van der Waals inter-molecular bonding in crystalline organic semiconductors. In these materials the charge mobility generally exhibits a "metallic-like" power-law behavior, with no sign of thermally activated hopping characteristic of carrier self-localization, despite apparent mean-free-paths comparable or lower than the inter-molecular spacing. Our results show that such puzzling transport regime can be understood from the simultaneous presence of band carriers and incoherent states that are dynamically localized by the thermal lattice disorder.