Printable High‐Aspect Ratio and High‐Resolution Cu Grid Flexible Transparent Conductive Film with Figure of Merit over 80 000

Abstract

Figure of merit (FOM), the ratio of electrical conductance to optical transparency, is an important metric to evaluate transparent conductive film (TCF). The conductivity of commonly used flexible TCF such as indium tin oxide is generally limited and their FOM is lower than 300. In this study, a high‐performance copper (Cu) metal‐mesh TCF with the highest FOM ever reported, up to 8 × 104, is fabricated through an additive manufacturing process of blading a silver seed layer and selective electroplating of Cu. With this strategy, Cu metallic lines completely constrained in roll‐to‐roll imprinted microgrooves achieve high aspect ratio of 2 with 4 µm width and 8 µm depth, which has very clean and smooth edges. This embedded Cu metal mesh exhibits an ultralow sheet resistance down to 0.03 Ω □−1 at 86% optical transmittance. It is demonstrated that the Cu metal mesh has remarkable mechanical flexibility, high environmental stability at high temperature and humidity, and durability over repeated heating cycles. The Cu metal mesh is employed as a flexible transparent heater to attach to the windshield of a car, showing rapid heating at low voltage and effective removal of snow.

Transparent Heaters: A Review

“…Chen et al reported recently a copper grid TH with an outstanding Haacke's FoM over 7820.10 −3 Ω sq −1 (see Figure 1c), and a fast heating rate at low voltage. [ 56 ] This clearly illustrates the efficiency of such technology as TH.…”

“…The arrows below represent roughly the typical maximum steady‐state temperatures for the main TH technologies. c) Optical transparency versus sheet resistance diagram for different TH technologies based on transparent conductive oxides (TCO), [ 14,33,58–60 ] carbon nanotubes (CNT), [ 27,33,61 ] graphene, [ 57,62,63 ] metallic nanowire (MNW) networks, [ 64–70 ] metallic grids‐meshes, [ 56,71–76 ] conductive polymers, [ 49,50,77,78 ] and nanocomposites. [ 22,48,51,79–81 ] The dashed lines correspond to different values of Haacke's FoM: 10 000, 1000, 100, 10, 1 times 10 −3 Ω sq −1 .…”

“…[ 72,112,148 ] However, the thermal and electrical stability of these metallic‐based THs can be a severe issue. However, as shown by Chen et al, [ 56 ] Cu based grids made from a Ag seed layer and a subsequent electroplating of Cu imprinted microgrooves exhibit very good performances. Indeed, sheet resistance down to 0.03 Ω sq −1 associated with a transmittance of 86% was demonstrated.…”

“…Many demo products have been fabricated, like defoggers/defrosters for car windows or side mirrors ( Figure a,b), made of patterned AgNWs, [ 232,233 ] AgNFs, [ 234 ] Cu grids [ 56 ] or Ni/Ag microgrids. [ 198 ] A demo motorcycle visor (Figure 16c) dip‐coated with PEDOT:PSS‐EG was fabricated and can be defrosted in a few seconds with a low voltage.…”

“…Reproduced with permission. [ 56 ] Copyright 2019, Wiley‐VCH. b) Photographs of the Ag/Ag 2 O‐NF/(index matching layer)IML heater‐integrated automobile windshield at i) turn‐off and ii) turn‐on modes.…”