Abstract
Transparent conductive films (TCFs) are essential components in many optoelectronic devices. Indium tin oxide (ITO) that possesses high transmittance ( > 90 T%) and low sheet resistances ( <10 Ωsq−1 ) has been widely employed in TCFs. The development of flexible electronic devices drives the need of the TCFs on flexible substrates. However, the brittleness of ITO and the low throughput of the vapor-phase sputtering process on plastic substrate restricted the applicability of ITO on the flexible electronic devices. Looking for alternatives to the next-generation TCFs becomes imperative. Cu nanowires (NWs) have become a promising alternative solution for TCFs by forming a NW network on a transparent substrate. Cu NWs have superior electrical conductivity and flexibility. Nano-twinned Cu NWs have exhibited high mechanical strength, good conductivity, and moreover, superior electromigration resistance, which can be an excellent material to the NW-based TCFs. Still, the sheet resistance of Cu NWs films can easily increase due to the formation of copper oxides and leads to a severe reliability issue. In this study, Cu NWs were synthesized by pulsed electrodeposition with porous anodic aluminum oxide (AAO) templates at low temperature. To improve their anti-oxidation property, we develop a method that can uniformly coat a thin layer of silver on the Cu NWs through a galvanic replacement reaction. The microstructure of Cu NWs and silver shell have been examined by transmission electron microscopy (TEM). The evolution of electrical resistivity for single Cu-Ag NWs was measured as a function of time by a four-point probe method. A transfer printing approach was used to fabricate the TCFs with Cu-Ag NWs. The pressure applied for the transfer printing process has been optimized to obtain a TCF with RS = 41 Ω/sq and T = 88.9 %, which gives a good figure of merit (FOM) up to 70. The Cu-Ag NWs film has demonstrated good anti-oxidation ability after thermal aging at 85 °C for 300 hours. Meanwhile, the sheet resistance of Cu-Ag NWs film remained unchanged after 1000 bending cycles, which shows the film has excellent flexibility. In summary, the Cu-Ag core-shell NWs show the good chemical stability that are able to improve the performance and reliability of the Cu NWs-based TCFs.