Electroplated metal grid/surface embedded silver nanowire hybrid structure for flexible transparent electrode

Abstract

Currently, flexible opto-electronic devices are under an intense spotlight with the increasing demand for future wearable electronics. Especially, flexible transparent conducting electrode (TCE) is necessary component for several opto-electronic devices such as flexible touch-screen panel, organic light-emitting diode (OLED) and organic solar cell (OSC). Tin doped indium oxide (ITO), the most commonly used material for TCE, has several drawbacks such as scarcity of indium, inherent brittleness, requirement of vacuum and high temperature process. These disadvantages make ITO not suitable for flexible opto-electronic devices. Carbon based materials such as graphene, carbon-nanotube (CNT), conducting polymer and metal nanowire are alternative materials for replacing ITO. Among them, metal nanowire is promising material substituting ITO due to its high transparency, low sheet resistance and superior flexibility. However, metal nanowire TCE still has several problems such as junction resistance between metal nanowire networks and thermal/chemical instability. Metal grid is emerging structure because of its continuous electron pathway and 100% transparency between grid lines. Also, its performance can be easily controlled by tuning line width, line spacing and thickness. However, vacuum deposition and high temperature process are still considered as weakness of metal grid. In this research, metal grid/surface embedded silver nanowire (AgNW) hybrid structure is proposed as new approach. Metal grid was fabricated by electroplating. Surface embedded AgNW glass-fabric reinforced plastic film (AgNW-GFRHybrimer) was used as flexible transparent conductive substrate and applied as seed layer for electroplating. Additional seed layer do not have to deposit because conducive layer in GFRHybrimer is used for seed layer. Metal grid/AgNW hybrid TCE exhibits excellent opto-electrical performance (Ag grid: 87%/ $13 \Omega /sq$, Cu grid: 74.7 / $160m \Omega /sq$), high thermal stability (Ag grid: $250^\circ C$/720min, Cu grid: $200^\circ C $/600min) and superior flexibility (bending radius = 1 mm, 2000cycles). Finally, 4-wire resistive type touch-screen panel was fabricated using metal grid/AgNW hybrid TCE to demonstrate its potential for actual opto-electronic devices. Fabricated touch-screen panel was clearly operated. This new approach, which is all-solution processed metal grid based on AgNW, can be the most promising candidate for next generation TCE platform of various flexible opto-electronics. For future, fabrication process can be extended to scalable and large area manufacturing.