Single-Crystal Organic Charge-Transfer Interfaces probed using Schottky-Gated Heterostructures

TL;DR

This study uses Schottky-gated heterostructures to investigate charge transfer and electron transport at the interface of two organic single crystals, revealing band-like conduction and high electron mobility.

Contribution

It provides detailed insights into the electronic structure and transport mechanisms at organic heterointerfaces using a novel gating approach.

Findings

Interfacial transport is due to electrons with band-like behavior.

Electron mobility reaches ~1 cm2V-1s-1 at 30 K.

Interfacial electron density decreases linearly with temperature.

Abstract

Organic semiconductors based on small conjugated molecules generally behave as insulators when undoped, but the hetero-interfaces of two such materials can show electrical conductivity as large as in a metal. Although charge transfer is commonly invoked to explain the phenomenon, the details of the process and the nature of the interfacial charge carriers remain largely unexplored. Here we use Schottky-gated heterostructures to probe the conducting layer at the interface between rubrene and PDIF-CN2 single crystals. Gate-modulated conductivity measurements demonstrate that interfacial transport is due to electrons, whose mobility exhibits band-like behavior from room temperature to ~ 150 K, and remains as high as ~ 1 cm2V-1s-1 at 30 K for the best devices. The electron density decreases linearly with decreasing temperature, an observation that can be explained quantitatively based on the heterostructure band diagram. These results elucidate the electronic structure of rubrene-PDIF-CN2 interfaces and show the potential of Schottky-gated organic heterostructures for the investigation of transport in molecular semiconductors.