Transport in organic semiconductors in large electric fields: From thermal activation to field emission

TL;DR

This study investigates charge transport mechanisms in organic semiconductors under large electric fields, revealing a transition from thermally activated hopping to field-driven tunneling at low temperatures.

Contribution

It provides experimental evidence of transport crossover in organic semiconductors, highlighting the importance of field effects and cautioning against exotic interpretations.

Findings

Transport at room temperature is thermally activated with Poole-Frenkel enhancement.

At low temperatures and high voltages, transport becomes temperature independent.

Data suggests a transition to field-driven tunneling at low temperatures.

Abstract

Understanding charge transport in organic semiconductors in large electric fields is relevant to many applications. We present transport measurements in organic field-effect transistors based on poly(3-hexylthiophene) and 6,13-bis(triisopropyl-silylethynyl) pentacene with short channels, from room temperature down to 4.2 K. Near 300 K transport in both systems is well described by thermally assisted hopping with Poole-Frenkel-like enhancement of the mobility. At low temperatures and large gate voltages, transport in both materials becomes nearly temperature independent, crossing over into field-driven tunneling. These data, particularly in TIPS-pentacene, show that great caution must be exercised when considering more exotic (e.g., Tomonaga-Luttinger Liquid) interpretations of transport.