One-pot multi-step synthesis of high-aspect-ratio Cu nanowires based on an environment-friendly manner for low-cost and high-performance transparent conductive films

Abstract

High-aspect-ratio Cu nanowires (NWs) were synthesized based on an environment-friendly synthesis method in which aqueous Cu–Cl complexes were reduced to Cu atoms in a weak ascorbic acid solution. Constant reaction temperatures led to many reduced Cu atoms relative to NWs and then the synthesized Cu atoms were deposited on the end and side faces of Cu NWs, resulting in low aspect ratios. Two-step temperature synthesis was suggested to suppress Cu atoms during the Cu NW growth. High temperatures during the early reaction stage maximized NW seeds and low temperatures in the late stage decreased the number of Cu atoms under precisely controlled temperature and temperature drop time, leading to Cu deposition on the end faces rather than side faces. Additionally, optimum Cu-source additions continuously facilitated the preferential growth in length of Cu NWs. The one-pot multi-step synthesis controlled the reduction rate of Cu complexes and substantially increased the aspect ratio of Cu NW from 313 to 760, showing that the precise control was suitable for changing the NW sizes. Finally, transparent conductive films comprising the NWs showed high performances (transmittance = 90.8 %, sheet resistance = 94 Ω/sq).