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Abstract
Controlling the growth behavior of organic semiconductors (OSCs) is essential because it determines their optoelectronic properties. In order to accomplish this, graphene templates with electronic‐state tunability are used to affect the growth of OSCs by controlling the van der Waals interaction between OSC ad‐molecules and graphene. However, in many graphene‐molecule systems, the charge transfer between an ad‐molecule and a graphene template causes another important interaction. This charge‐transfer‐induced interaction is never considered in the growth scheme of OSCs. Here, the effects of charge transfer on the formation of graphene–OSC heterostructures are investigated, using fullerene (C60) as a model compound. By in situ electrical doping of a graphene template to suppress the charge transfer between C60 ad‐molecules and graphene, the layer‐by‐layer growth of a C60 film on graphene can be achieved. Under this condition, the graphene–C60 interface is free of Fermi‐level pinning; thus, barristors fabricated on the graphene–C60 interface show a nearly ideal Schottky–Mott limit with efficient modulation of the charge‐injection barrier. Moreover, the optimized C60 film exhibits a high field‐effect electron mobility of 2.5 cm2 V−1 s−1. These results provide an efficient route to engineering highly efficient optoelectronic graphene–OSC hybrid material applications.
Highlights
Controlling the growth behavior of organic semiconductors (OSCs) is of graphene constitute a basal plane with essential because it determines their optoelectronic properties
The optimized C60 film exhibits a high field-effect electron mobility of 2.5 cm2 V−1 s−1. These results provide an efficient route to useful growth template for semiconductors, especially organic semiconductors (OSCs).[6,7]
We demonstrate that an epitaxial growth of a vacuumdeposited fullerene (C60) thin film on a graphene template can be controlled by tuning charge transfer between them
Summary
We first investigated the transfer of electrons from graphene to C60. Analyses using ultraviolet photoelectron spectroscopy, Kelvin probe force microscopy, and Raman spectroscopy revealed that the adsorption of C60 molecules induced p-type doping of graphene (Figure S2, Supporting Information). At VG > −40 V, the RCh–VG curve shifted to the right; this change indicates that electrons were transferred from graphene to C60 (Figure 1b). When plotted versus ng,bare (Figure 1c), extracted ΔnCT showed no charge transfer between graphene and C60 when ng,bare was less than a critical value, nc = −4.4 × 1012 cm−2. The absence of charge transfer when ng,bare < nc is attributed to the EF of graphene being lower than the LUMO level of the C60 adsorbates (Figure 1d, left). As a result of this charge transfer, an electric field is generated between the graphene and the C60, so the vacuum level at the interface becomes tilted so that the EF of the graphene and the LUMO level of the C60 are aligned (Figure 1d, right). This downshift of the LUMO level upon charge transfer can substantially stabilize C60 adsorbates on graphene.[17]
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