Transparent Cu grid prepared by inkjet printing with Cu nanoparticle Ink

Abstract

We report on inkjet-printed transparent Cu grid electrodes for use in printable optoelectronic devices. The inkjet-printed Cu grid electrode exhibited a low resistivity of 2.2 × 10⁻⁶ ohm-cm after rapid thermal annealing (RTA) at 500 °C with a N₂ and H₂ gas mixture under ambient conditions. The optical transmittance of the inkjet-printed Cu grid was critically affected by the grid separation distance. At a grid separation distance of 3 mm, the inkjet-printed Cu grid showed an optical transmittance of 89.66% at a wavelength of 550 nm. The microstructure of the inkjet-printed Cu grid was evaluated by using X-ray diffraction and high-resolution electron microscopy before and after rapid thermal annealing. The as-printed Cu nanoparticles, which existed in the Cu₂O phase, were completely transformed into a metallic Cu electrode after rapid thermal annealing at temperatures above 400 °C. This process occurred because the Cu₂O nanoparticles were effectively reduced by RTA under a N₂ and H₂ mixture ambient, which indicates that RTA is a promising reduction process for transparent inkjet-printed Cu grid electrodes.