(Invited) A New Category of Transparent Conductive Films: Printed Carbon Nanotube Hybrids
Authors: Prada Silvy Ricardo Alfredo , Arthur David Joseph 
Published: February 2020

Transparent Conductive Films (TCFs) are used in a wide range of commercial applications, including information displays, capacitive touch sensors, solar photovoltaic modules, EMI shielding windows, transparent heaters, etc. There are many materials that are transparent and many materials that are electrically conductive, but there are very few materials that are both. Indium Tin Oxide (ITO) has dominated the TCF materials market for the past four decades, because of its excellent optoelectronic performance (high transparency, low sheet resistance, low haze, and excellent environmental stability). ITO is typically vacuum coated onto glass sheets or flexible plastic film substrates, with circuit patterns formed by laser ablation or chemical etching methods.

The market for TCF materials is forecasted to exceed $5 billion by 2022, with more than half of the market being comprised of TCFs on flexible plastic films (vs. glass) by that date. It is important to note that ITO has well-known shortcomings on flexible plastic films. First, ITO is a brittle ceramic, so it can easily crack when flexed. This is a major limitation, as many product designs are moving towards thinner, flexible and 3D-shaped form factors. Second, ITO’s optoelectronic properties are much better on glass, due to the temperature limitations of plastic. This is a major limitation, as nearly all product designs work better with lower sheet resistance. Third, circuit patterning of ITO on flexible plastic films is expensive, due to handling damage (cracking of circuit features). This is a major limitation, as many product designs are moving towards thinner and larger area substrates, which are even more difficult to handle.

Thus, there is an unmet market need for an ITO Alternative that addresses the shortcomings of ITO on flexible plastic films. Several TCF material categories have been established, but there has been limited commercial traction…

One category is conductive polythiophene materials (PEDOT), which offer the advantages of low-cost circuit patterning (can be printed) and excellent flexibility and thermoformability. However, PEDOT is lacking in two key areas: 1) sheet resistance is higher than ITO on plastic films at the same transparency; 2) environmental stability is questionable, especially during UV and high temperature / humidity aging tests. These two shortcomings have made PEDOT a niche player.

A second category is Carbon Nanotubes (CNTs), which offer all the advantages of PEDOT without compromising environmental stability. However, CNT TCFs have even higher sheet resistance than PEDOT at the same transparency. This shortcoming has made CNTs irrelevant for most TCF applications.

A third category is Metal Mesh (MM), which are essentially printed (or etched) metal mesh patterns that have large enough open areas to have high transparency (like a window screen) and large enough cross-sectional area of metal to have low sheet resistance. MM TCFs are comprised of Silver &/or Copper. MM offers significantly lower sheet resistance than ITO on plastic films at the same transparency. MM also offers far superior flexibility than ITO. However, MM has is lacking in two key areas: 1) the metal lines comprising the MM are typically visible and this can be distracting – although this can be addressed with fine line printing (line widths ≤ 6µm), the MM cost is much higher; 2) creating TCF circuit patterns is expensive.

A fourth category is Silver Nanowires (AgNWs), which offer all the advantages of MM without compromising aesthetics (MM visibility). However, AgNW is lacking in three key areas: 1) environmental stability is questionable, especially during UV and high temperature / high humidity aging tests; 2) robust electrical connections to AgNW are challenging due to the insulating polymer used to encapsulate AgNWs; 3) creating TCF circuit patterns is expensive.

Despite their shortcomings, AgNW and MM appear to be gaining the most commercial traction, yet market penetration is still low.

CHASM has recently created a new TCF category called Printed CNT Hybrids, which are made by combining CNTs with either AgNW or MM technologies to create a Hybrid solution that is superior to CNT, AgNW or MM technologies alone. CHASM is marketing its portfolio of Printed CNT Hybrids under the AgeNT™ brand.

This presentation describes how CHASM combines its distinguished CNT synthesis capabilities (CoMoCAT™ technology) with proprietary ink formulation capabilities (V2V™ technology) to create AgeNT™ printed CNT Hybrid TCFs that are positioned to become a leading ITO Alternative.

Figure 1