Flexible grid-mesh electrodes fabricated by electroless copper plating on corona-treated PET substrates and coating with graphene for transparent film heaters

Abstract

In this study, we present solution-based processes for producing copper (Cu) meshes which can be utilized as transparent conductive electrodes (TCEs) for flexible film heaters. The surface modification of polyethylene terephthalate (PET) substrates was done via corona treatment at atmospheric pressure and room temperature. The Cu layer was deposited on the corona-treated PET substrate via electroless plating and then patterned via lithography to have mesh dimensions of a 200 μm line-to-line spacing and a 6 μm line width. Also, graphene was coated on the Cu mesh via electrophoretic deposition (EPD). The chemical and physical changes in the PET surfaces were characterized according to the corona treatment conditions. The measurements of contact angles and surface energies of the corona-treated PET substrates indicated that the PET surfaces changed from hydrophobic to hydrophilic after corona treatment, leading to the improvement in the adhesion between the PET substrates and the Cu meshes. The flexibility of the Cu meshes was inspected by performing bending and twisting tests and by directly measuring the adhesion strength between the Cu layers and the PET substrates through scratch tests. The effects of graphene coating on the characteristics of the Cu meshes were examined in terms of their surface morphologies, electrical sheet resistances, transmittances and reflectances in the visible-light wavelength range, and color differences. Finally, the film heaters produced by employing the graphene-coated Cu meshes yielded a temperature rise over 85 °C with a response time shorter than 20 s.