A simple and flexible route to large-area conductive transparent graphene thin-films

• Solution-processed conductive, flexible and transparent graphene thin films synthesized from graphite.
• Donor and acceptor type graphite intercalation compounds used as precursors.
• Surfactant-free solvents to obtain stable colloidal dispersions for realizing films by lift-up transfer to virtually any substrate of interest.
• Thickness-tunable sheet resistances.
• Au-doping decreases the sheet resistance by a factor of 5 and is stable in an inert atmosphere.

Solution-processed conductive, flexible and transparent graphene thin films continue drawing attention from science and technology due to their potential for many electrical applications. Here, an up-scalable method for the solution processing of graphite to graphene and further to self-assembled large-area conductive transparent thin-films is presented. The method proceeds via the graphite intercalation route followed by thermal expansion to obtain expanded graphite. The resulting material is dispersed in a surfactant-free mixture of isopropanol and propylene glycol to obtain a stable colloidal dispersion. A graphene thin film is subsequently formed by self-organization at an oil/water interface followed by lift-up transfer to virtually any substrate of interest. Thermally annealed thin-films exhibit a thickness-tunable sheet resistances of between 10 and 0.8 kΩ/□ with transparencies between 75% and 45% at 500 nm wavelength, respectively. Additional Au-doping decreases the sheet resistance by a factor of 5. Heating doped films to temperatures above 380 K or exposure to ambient conditions significantly increases the sheet resistance as a result of decreasing charge carrier concentration. The presented method is a simple, up-scalable and thus competitive alternative to other techniques for large area graphene film production.

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