Inkjet Printing Graphene-Based Transparent Conductive Films
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Inkjet Printing Graphene-Based Transparent Conductive Films Pei He1 and Brian Derby1 1
School of Materials, University of Manchester, Manchester, M13 9PL, United Kingdom.
ABSTRACT Graphene is a strong contender as a material to replace indium tin oxide as the transparent conductor of choice for electronic applications due to its exceptional electrical and optical properties. In this work, we present a study of graphene oxide (GO) films produced by inkjet-printing. The printed GO films are reduced using hydriodic acid (HI) and acetic acid vapour at low temperature. The reduced GO (rGO) films displayed good optical and electrical properties with a sheet resistance 6.8 kΩ/□ at a transmittance of 80%. In addition, we show that the conductivity of rGO films is related to both the size of individual GO sheets in the ink and the thickness of printed films. The rGO films using large size GO sheets displayed a thicknessindependent conductivity of ~ 4 × 104 S/m, while the rGO films using small size GO sheets showed a thickness-independent conductivity of ~ 1.7 × 104 S/m. These properties are comparable to graphene films produced by solvent exfoliation. In summary, we demonstrate a scalable and potentially low-cost technique to produce rGO transparent films and a route to improve the conductivity of rGO films by controlling size of GO sheets in the ink. INTRODUCTION Graphene has attracted extensive attention not only for its exceptional electrical, mechanical, chemical and optical properties [1], but also because it can be produced either by exfoliation from natural graphite or by chemical vapour deposition (CVD). This has made it attractive for high performance and large area electronic applications, especially as a transparent conductor [2]. Among the various methods used to synthesize graphene-based transparent conductive films (TCFs), the CVD technique is known to produce high-quality and large-area graphene on Ni films and Cu foils, which can be further transferred to glass or polyester substrates as TCFs [1-3]. However, CVD deposited graphene requires dedicated reactors and complex transfer from a metal growth substrate to a transparent substrate, which may lead to high costs [4]. Moreover, the large area graphene film is easy to wrinkle or damage during the transfer process. All these problems potentially limit the use of the CVD graphene for large-area and low-cost applications. Alternatively, synthesis of graphite oxide from natural graphite, followed with exfoliation into mono-layer GO and finally reduction to remove the oxygen groups is a more cost efficient way to produce large volumes of graphene or graphene-like materials [5]. Owning to the presence of carboxylic acid and phenolic hydroxyl groups, GO sheets can form stable homogeneous dispersions in aqueous and other polar organic solvents without surfactants [6]. TCFs based on GO sheets have been produced via well-established fabrication methods, including vacuum filtration [7], spin-coating [8], Langmuir-Blodgett assembly [9], and inkjet printing [10]. Among
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