Exploring Charge Transport Mechanisms and Conduction Limits in Rubrene Single Crystals

Abstract

This dissertation focuses on fundamental research on the frontier of organic electronics, aiming to find answers to some long-standing puzzles related to electrical conduction in the benchmark single crystal organic semiconductor known as rubrene. Emphasis is on determining the intrinsic charge transport mechanism in rubrene single crystals, as the crystalline order in these samples facilitates better understanding of fundamental structure-property relationships. To further explore the conduction limits in rubrene single crystals, high densities of charge carriers are injected using the liquid-gating technique, and intriguing and unusual physical phenomena, such as negative transconductance and cooling-rate-dependent charge transport, have been observed. Chapters 1-4 summarize the background information for this dissertation. Chapter 5 focuses on the isotope effect on field-effect mobility in rubrene single crystals to determine the best theoretical model for charge transport in high mobility organic semiconductors. Chapter 6 explains why very few organic semiconductors exhibit intrinsic, band-like transport by revealing correlated electronic and structural disorder using scanning Kelvin probe microscopy. Chapter 7 focuses on the use of dipolar liquid to accumulate charge at rubrene crystal surfaces while maintaining the high mobility. Chapter 8 explores charge transport phenomena near the maximum conductivity of rubrene single crystals and proposes the limiting factors for charge transport. Overall, this work helps to better understand intrinsic charge transport mechanisms and conduction limits in high mobility organic semiconductors.