Fabrication of air-stable, transparent Cu grid electrodes by etching through a PVA-based protecting layer patterned using a screen mesh

Abstract

As an alternative to conventional indium-tin-oxide (ITO) electrodes, a transparent Cu grid electrode was fabricated by etching a sputtered Cu on a flexible polyethylene naphthalate film through a polyvinyl alcohol (PVA)-based protecting layer. The masking pattern of the PVA-based polymer on the Cu was generated by evaporation of an aqueous solution containing PVA-based polymers using a screen mesh as a template. The solution formed a stable liquid-bridge network between contact points of the screen mesh and the substrate after being dropped onto the mesh placed on the substrate. Drying of the solution yielded grid or dotted patterns, depending on the concentration of PVA. Etching of the Cu film covered with the PVA pattern was done with a FeCl₃ methanolic solution to form a grid-patterned Cu electrode. Although some underetching was observed, adjusting the etching time gave a fine line network of Cu with the PVA coated thoroughly. The Cu grid electrode showed a transparency of 87.2 ± 5.2% at 550 nm and 6.1 ± 5.3 Ω □⁻¹, which is comparable to or greater than that of the conventional ITO. Furthermore, we found that the PVA coating barrier significantly enhanced the oxidation resistance of the Cu grid electrode.