Laser Direct Writing of Heteroatom (N and S)-Doped Graphene from a Polybenzimidazole Ink Donor on Polyethylene Terephthalate Polymer and Glass Substrates.

In this paper, for the first time, a laser direct writing technique is reported to form S- and N-doped graphene patterns on thin (0.3 mm thickness) polyethylene terephthalate (PET) and glass substrates from a specially formulated organic polybenzimidazole (PBI) ink, without thermally affecting the substrates and without the need for a metallic precursor. Unlike standard graphene ink printing, postcuring at high temperatures is not needed here, thus avoiding potential substrate distortion and damages. A UV laser beam of 355 nm wavelength is used to generate photochemical reactions to break the CS bond (2.8 eV) from dimethyl sulfoxide (DMSO, a component of the PBI ink) and the CN bond (3.14 eV) of PBI and form N- and S-doped graphene on the substrates. The sheet resistance of the laser-induced graphene is as low as 12 Ω sq-1 on PET, matching that of indium-tin oxide (ITO). The laser-written doped graphene shows hydrophilic characteristics, unlike pristine graphene. The S- and N-doped graphene allows the tailoring of bandgaps and thus controlling electrical and chemical properties. The optical transparency of the written graphene is below 10% which could be improved in the future. Potential applications include printing of flexible circuits and sensors, and smart wearables.