Abstract
The increasing demand for flexible electronic devices drives the need for alternative materials other than indium tin oxide (ITO) as transparent conducting films (TCFs). Dispersing metallic nanowires on a polymer substrate appears to be a good solution for flexible TCFs. Among various metallic nanowires (NWs) used in TCFs, Cu based NW has been considered a potential candidate because of its cost advantage and good electrical properties. In our previous study we introduced dense nanoscale twinning structure in Cu NWs that was deposited in porous anodic aluminum oxide (AAO) templates using pulsed electroplating process. However, oxidation is the detrimental problem for the application of Cu NWs in TCFs. In this study, we have successfully synthesized Cu-Ni core-shell NWs. First, the nanotwinned Cu NWs were released from AAO templates by a wet chemical method. They were coated a thin layer of Ni using a reducing agent, sodium borohydride, in ethylene glycol solvent. We optimized the reaction temperature to achieve a smooth Ni layer coating. Next, the Cu-Ni NWs were transferred onto a PET substrate to form a TCF through vacuum filtration method and pressing process. The TCF sheet resistance is substantially reduced from 31 K/sq. to 40 /sq. at a transmittance of 88% with the optimized pressure applied during the film transfer process. The TFC sheet resistance increases 3~10 /sq. after a 1000 cycles of dynamic bending and static bending tests. Finally, the Cu-Ni TCFs had a negligible increase in sheet resistance after heating at 85 C for several hundreds of hours. It achieves the goal of improving oxidation resistance of Cu NWs by forming a Cu-Ni core-shell structure.