Cu Mesh for Flexible Transparent Conductive Electrodes

Won-Kyung Kim, Seunghun Lee, Duck Hee Lee, In Hee Park, Jong Seong Bae, Tae Woo Lee, Ji-Young Kim, Ji Hun Park, Yong Chan Cho, Chae Ryong Cho, Se-Young Jeong
2015 Scientific Reports  
Copper electrodes with a micromesh/nanomesh structure were fabricated on a polyimide substrate using UV lithography and wet etching to produce flexible transparent conducting electrodes (TCEs). Well-defined mesh electrodes were realized through the use of high-quality Cu thin films. The films were fabricated using radio-frequency (RF) sputtering with a single-crystal Cu target-a simple but innovative approach that overcame the low oxidation resistance of ordinary Cu. Hybrid Cu mesh electrodes
more » ... re fabricated by adding a capping layer of either ZnO or Al-doped ZnO. The sheet resistance and the transmittance of the electrode with an Al-doped ZnO capping layer were 6.197 ohm/sq and 90.657%, respectively, and the figure of merit was 60.502 × 10 -3 /ohm, which remained relatively unchanged after thermal annealing at 200 °C and 1,000 cycles of bending. This fabrication technique enables the mass production of large-area flexible TCEs, and the stability and high performance of Cu mesh hybrid electrodes in harsh environments suggests they have strong potential for application in smart displays and solar cells. Transparent conducting electrodes (TCEs), which have high optical transparency and high electrical conductivity, are widely used in numerous optoelectronic devices, including organic/inorganic light-emitting diodes, liquid-crystal displays, touch-screen panels, supercapacitors, and solar cells 1-7 . Historically, the use of indium tin oxide (ITO) has dominated in the TCE industry; however, some critical problems are associated with the mechanical, thermal and chemical stability of ITO. The scarcity of indium and its increasing price are additional factors that make ITO undesirable in TCE applications. Thus, efforts have been devoted to the development of alternatives to ITO (e.g., conducting polymers, Al-doped ZnO and metal thin films); however, these alternatives have been unsatisfactory for industrial demands 8-10 . In recent years, however, micromaterials and nanomaterials, including carbon nanotubes, graphene, and metal wire/particle networks, have offered a new paradigm for the TCE industry 11-20 . Among these, metal nanostructure network TCEs have exhibited high performance and are suitable for large-area applications. Various fabrication methods have been employed, such as spin (or spray) coatings of nanowire dispersions 11-17 , electronic spinning 17-19 , and lift-off processes with nanotemplates 21-23 . Silver (Ag), in particular, has attracted great interest for TCE applications because of its superior electrical conductivity, and various fabrication processes have been investigated to simplify the manufacturing process and to improve performance 4, [13] [14] [15] [16] [17] [18] [20] [21] [22] . However, Ag is not suitable for use in mass production requiring low costs. Copper (Cu) has high electrical conductivity comparable to that of Ag, and Cu is much less expensive and more abundant than Ag 11,23 . Recently, transparent conductive films have been reported
doi:10.1038/srep10715 pmid:26039977 pmcid:PMC4454070 fatcat:3ovq7srvcre53dsewiwl2mc7ny