Freeing electrons from extrinsic and intrinsic disorder yields band-like transport in n-type organic semiconductors

TL;DR

This study demonstrates that through specific molecular design, it is possible to mitigate both intrinsic and extrinsic disorder in n-type organic semiconductors, enabling band-like charge transport despite the typical sensitivity to disorder.

Contribution

The paper provides experimental and theoretical evidence that molecular design can effectively reduce disorder, leading to band-like transport in n-type organic semiconductors.

Findings

Molecular design can free charge carriers from disorder.

Band-like transport achieved in n-type organic semiconductors.

Disorder control improves charge mobility.

Abstract

Charge transport in organic semiconductors is notoriously extremely sensitive to the presence of disorder, both intrinsic and extrinsic, especially for n-type materials. Intrinsic dynamic disorder stems from large thermal fluctuations both in intermolecular transfer integrals and (molecular) site energies in weakly interacting van der Waals solids and sources transient localization of the charge carriers. The molecular vibrations that drive transient localization typically operate at low-frequency (< a-few-hundred cm-1), which renders it difficult to assess them experimentally. Hitherto, this has prevented the identification of clear molecular design rules to control and reduce dynamic disorder. In addition, the disorder can also be extrinsic, being controlled by the gate insulator dielectric properties. Here we report on a comprehensive study of charge transport in two closely related n-type molecular organic semiconductors using a combination of temperature-dependent inelastic neutron scattering and photoelectron spectroscopy corroborated by electrical measurements, theory and simulations. We provide unambiguous evidence that ad hoc molecular design enables to free the electron charge carriers from both intrinsic and extrinsic disorder to ultimately reach band-like electron transport.