Abstract
The unique density of states and exceptionally low electrical noise allow graphene-based field effect devices to be utilized as extremely sensitive potentiometers for probing charge transfer with adsorbed species. On the other hand, molecular level alignment at the interface with electrodes can strongly influence the performance of organic-based devices. For this reason, interfacial band engineering is crucial for potential applications of graphene/organic semiconductor heterostructures. Here, we demonstrate charge transfer between graphene and two molecular semiconductors, parahexaphenyl and buckminsterfullerene C60. Through in-situ measurements, we directly probe the charge transfer as the interfacial dipoles are formed. It is found that the adsorbed molecules do not affect electron scattering rates in graphene, indicating that charge transfer is the main mechanism governing the level alignment. From the amount of transferred charge and the molecular coverage of the grown films, the amount of charge transferred per adsorbed molecule is estimated, indicating very weak interaction.
Highlights
Graphene has a significant potential to be used as a new transparent conductive electrode material in flexible and wearable electronics, optoelectronics, and energy applications[1, 2]
We study in-situ the effect that deposited molecular crystals have on the transfer curves of graphene field effect transistors (FETs), and probe the formation of the interfacial dipole
The custom-built hot wall epitaxy (HWE) chamber used in this study has three electrical contacts attached to the sample holder, which allow to probe and tune electrical properties of the samples prior and during the growth
Summary
Graphene has a significant potential to be used as a new transparent conductive electrode material in flexible and wearable electronics, optoelectronics, and energy applications[1, 2]. In addition to high transparency, high mechanical strength, flexibility, thermal as well as chemical stability, and ease of functionalization, there are crucial advantages of graphene as an electrode material in organic electronics. These are mainly based on the favorable band alignment with many organic semiconductors and on their impeccable growth morphologies on graphene, which relies on the van der Waals (vdW) nature of the interface[3]. Interfaces between graphene and metal oxides have been investigated as effective hole-injection layers in organic light emitting diodes[20, 21], exhibiting p-type doping of graphene through charge transfer and formation of an interfacial dipole. In-situ electrical characterization was employed to reveal the relation between SiO2 and the effective p-type doping of graphene under ambient conditions[31], showing the necessity of both, water and oxygen in this process
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