A DFT Study on the Electronic Structures and Conducting Properties of Rubrene and its Derivatives in Organic Field-Effect Transistors

Huipeng Ma,Na Liu,Jin-Dou Huang

doi:10.1038/s41598-017-00410-6

Abstract

We systematically studied the electronic structures and conducting properties of rubrene and its derivatives reported recently, and disscussed the influences of electron-withdrawing groups and chemical oxidation on the reorganization energies, crystal packing, electronic couplings, and charge injection barrier of rubrene. Hirshfeld surface analysis and quantum-chemical calculations revealed that the introduction of CF3 groups into rubrene decreases the H···H repulsive interaction and increases intermolecular F···H/H···F attractive interactions, which resulted in the tight packing arrangement and the increase of the electronic couplings, and finally cause the higer intrinsic hole-mobility in bis(trifluoromethyl)-dimethyl-rubrene crystal (μh = 19.2 cm2 V−1 s−1) than in rubrene crystal (μh = 15.8 cm2 V−1 s−1). In comparison, chemical oxidation reduces charge-carrier mobility of rubrene crystal by 2~4 orders of magnitude and increased the hole and electron injection barrier, which partly explains the rubrene-based field-effect transistor performance degrades upon exposure to air. Furthermore, we also discussed the influence of structural parameters of carbon nanotube (CNT) electrode on charge injection process, which suggests that the regulation of CNT diameters and increasing in thickness is an effective strategy to optimize CNT work functions and improve n-type OFET performances based on these organic materials.

Highlights

We systematically studied the electronic structures and conducting properties of rubrene and its derivatives reported recently, and disscussed the influences of electron-withdrawing groups and chemical oxidation on the reorganization energies, crystal packing, electronic couplings, and charge injection barrier of rubrene
Hirshfeld surface analysis and quantum-chemical calculations revealed that the introduction of CF3 groups into rubrene decreases the H···H repulsive interaction and increases intermolecular F···H/H···F attractive interactions, which resulted in the tight packing arrangement and the increase of the electronic couplings, and cause the higer intrinsic holemobility in bis(trifluoromethyl)-dimethyl-rubrene crystal than in rubrene crystal
We systematically studied the influences of electron-withdrawing group CF3 and chemical oxidation on the reorganization energies, crystal packing, electronic couplings, and charge injection barrier of rubrene

Summary

Introduction

We systematically studied the electronic structures and conducting properties of rubrene and its derivatives reported recently, and disscussed the influences of electron-withdrawing groups and chemical oxidation on the reorganization energies, crystal packing, electronic couplings, and charge injection barrier of rubrene. Xie et al further examined the ambipolar charge injection and transport properties of bottom contact single crystal field-effect transistors (SC-FETs) based on bis(trifluoromethyl)-dimethyl-rubrene (fm-rubrene, as shown in Fig. 1), by employing carbon nanotube (CNT) electrodes; and its benchmark ambipolar mobilities could be achieved, reaching 4.8 cm[2] V−1 s−1 for hole transport and 4.2 cm[2] V−1 s−1 for electron transport[5]. To deeply understand the effect of molecular structure on solid-state packing and resulting charge-carrier transport, we systematically studied the electronic properties of rubrene and their derivatives (see Fig. 1), and discussed the influences of the electron-withdrawing group and chemical oxidation on the reorganization energies, molecular packing structures, electronic couplings, HOMO/LUMO distributions, electron affinity (EA) values and ionization energy (IP) values of rubrene. Our theoretical investigations here could help to provide a fundamental understanding of substituent effect/chemical oxidation on rubrene and modification effect of CNT on metal electrode, enabling the rational design of high-performance OFETs with superior properties

Methods

Results

Conclusion