Opportunities for nanomaterials as conductive coatings

Recently completed market analysis conducted by NanoMarkets and published in its recent study ‘Conductive Coatings Markets: 2009 and Beyond’ indicate that the fastest growing opportunity in the conductive coatings market is in the area of nanomaterials.

While negligible in 2009, the company expects sales of conductive coatings using nanomaterials to reach more than $625 million by 2016.

There are two reasons for this rapid growth. First, nanomaterials offer superior conductivity. They are often inherently more conductive than the equivalent non-nano formulations.

Metallic nanoparticles are, for example, more conductive than simple metallic powders because of the higher surface area to volume ratio of nanoparticles.

In other cases - carbon nanotubes are a good example here - the additional conductivity is due to the physical characteristics of the nanostructure. Note that this is something quite new in the development of conductive coatings.

In the past, deviations from the use of industry standard metallic coatings - to metallic compounds or conductive polymers, for example - have been prompted not by improved conductivity, but by cost, environmental suitability or other secondary physical characteristics such as ease of deposition.

There is a growing list of applications for conductive coatings where this extra conductivity is more than just an advantage. It is actually a key market enabler (at least potentially) for the success of new products.

While enhanced conductivity is presumably always a good thing to have in conductive coatings, conductive nanocoatings with commercial potential can actually prove to be an enabling technology.

A case in point is in thin-film photovoltaic cells, where the primary measure of performance is energy conversion efficiency.

It has been shown in the lab that the best performing cells, the champion cells, as they are called, depend heavily on the quality of their electrode materials.

In some cases, certain kinds of photovoltaic materials may only be commercially useful in a given application if the conductive coatings used for electrodes are conductive enough to provide for adequate photovoltaic efficiencies.

Some future breakthrough in conductive nanomaterials could, for example, enable organic photovoltaic cells to become useful in areas ruled out today by the current low efficiencies.

The ‘rub’, as they say, lies in the words ‘future breakthrough.’ There are few cases today where conductive nanocoatings are used in practical applications and many of the early reports from the conductive coatings front are not especially impressive.

For example, coatings using single-walled carbon nanotubes have been used instead of indium-doped tin oxide (ITO) for display electrodes but, despite the high hopes, in practice have sometimes proved to have conductivity lower than that of commercially used ITO.

Nonetheless, nanomaterials are at an early stage of technological and commercial development and they do have the potential to make a leap forward in terms of price/performance ratios.

This cannot be said about most of the other alternatives to standard metallic coatings. Metallic oxide preparations have shown no appreciable performance improvements in a couple of decades, for instance.

There may be considerable potential for improvements with conventional conductive materials, but not revolutionary breakthroughs.

Only nanomaterials, or possibly composite materials in which such nanomaterials are a critical part of the mix, seem to offer an opportunity for what might be called ‘next generation’ conductive coatings.

Today, much of the work in conductive nanocoatings involves carbon nanotubes. But this is certainly not the only focus.

Other types of nanomaterials could also play an important role in this area, including non-carbon nanostructures (nanorods, nanowires etc, made from metallic oxides, for example) and especially coatings and pastes that use metallic nanomaterials (such as nanosilver).

The focus on nanotubes, ironically, reflects the fact that early attempts to launch an advanced carbon nanotube electronics based on nanotube transistors were rebuffed by the semiconductor industry (who preferred to stay with the silicon they knew) and led to a lot more technical difficulties than originally expected.

Responding to this, carbon nanotube electronics has begun to focus on less ambitious products and conductive coatings are an important part of this effort.

The two ‘big’ names in this effort are Eikos and Unidym, although there are other less prominent players in this space and there is also a considerable amount of activity in this area in university labs.

Unidym has been especially active and has targeted its carbon nanotube-containing conductive film as an ITO substitute for applications markets including touch screens, solar cells, flat-panel displays and solid-state lighting.

It should be noted, however, that mechanical robustness rather than conductivity is the main selling feature of these films at present.

The other type of nanomaterials used in conductive coatings is metallic nanoparticles. So far we are seeing two ways in which this approach is being developed with commercialised products in mind.

One of these is again, as with the Unidym example above, in the area of ITO replacement. The other involves nanopastes (usually silver nanopastes) for screen coating/printing.

In the ITO replacement space, the firm that is usually cited is Cambrios, which is marketing a solution-processable transparent conductive coating material (ClearOhm ink) and a transparent conductive-coated film (ClearOhm film).

The technology is based on high aspect ratio metallic particles (nanowires) which can be deposited via a low-cost, non-vacuum-based method.

Working with Sumitomo and Chisso Corporation, Cambrios is planning to focus on ITO replacement applications in the conventional LCD space.

Nanopaste development is, by contrast, more focused on replacing conventional metallic pastes in thick-film electronics. Not all thick-film electronics would be amenable to this kind of evolution to newer materials.

Unless price improvements were involved, and they seldom are, there are areas where nanopastes could bring only marginal advantages, if that, but there are other areas where the advantages could be manifest.

By way of illustration of where such pastes could be used, Advanced Nano Products (ANP) offers silver nanopastes that it says can be used in PDP electrodes, flexible PCBs, EMI shielding, solar cells, other flexible display and printed electronics applications, as well as low reflection and antistatic functions including conductive coatings on CRTs.

According to the company, one of its pastes is currently used in MLCC capacitors. Harima Chemical is another firm offering nanopastes of this kind.

Henkel Electronics, once the leaders in the field of thick film electronics, is known to have been working with researchers at UC Berkeley to develop high-performance, novel nanoparticle conductive materials for several years, with a commercial product announcement expected soon.

As noted earlier, the extra performance inherent in nanocoatings - mostly enhanced conductivity, but also the flexibility, physical resilience and thinness of coatings - can enable new types of products.

Again, the paradigmatic example here is organic photovoltaics, which lag all other kinds of PV in performance but where improvements in electrode material could help solve this problem and let OPV enter new markets.

Research has already shown that carbon nanotubes may be better in this regard than commonly used TCO materials in OPV cells.

OPV is a niche market at present. By contrast, the touch-screen display market is already well developed but it is really the tip of the iceberg.

Not only are touch screens themselves a rapidly growing product area, but they are just part of an even faster growing sector: touch-based computer input, an area generally referred to as haptics.

Haptics will not take off without some highly resilient and highly conductive electrode materials. Already there is considerable work being carried out to replace the ITO, which tends to crack after a lot of banging and poking with styluses and pens, with longer lasting, less brittle nanomaterials.

This work could well spill over into other areas where haptics is being applied such as robotics, gaming and medicine.

Sensors are seldom identified as an ‘opportunity’ by conductive coating manufacturers. Nonetheless, it seems likely that enhanced conductive materials/coatings could be important in meeting the needs of the sensor industry because high conductivity often translates into more sensitivity; and this again would seem to favour the use of nanomaterials coatings for electrodes.

Nanosilver pastes appear to have especially good prospects in the sensor industry since silver is the most conductive material known to man and conductivity translates into more sensitive sensing, as it were.

More specifically, in terms of actually enabling new kinds of sensors, we note the trend toward large-area sensors being created on plastic substrates. These often require electrode materials that are both highly conductive and can be worked with at modest temperatures, since high temperatures damage the substrate.

Nanosilver pastes may, again, be the solution here, since they typically need relatively low temperature after being deposited.

Another area where nanomaterials may prove useful and effective is lighting. Thus, various nanomaterials have been used in certain research environments for high-brightness LEDs, so perhaps there may be some new revenue generation possibilities coming from this direction too.

Conductive coatings, of course, are also widely used for EMI/RFI shielding and nanomaterials may also have some use here, since the effectiveness of metallic EMI/RFI shielding depends on the small size of the metal particles.

The kind of product that may have some potential is represented by Cima NanoTech’s nanosilver-based emulsion, which is being targeted toward the EMI/RFI sector.

Nanotubes have also attracted attention for EMI/RFI shielding and for certain electrostatic shielding (ESD) applications.

Applications outside the electrode space are of increasing importance because of the apparently unstoppable trend toward mobile computing, which is creating a growing need for more and better EMI/RFI shielding, and the trends in the semiconductor industry, creating a need for better ESD protection.

Conventional conductive coatings have not changed all that much for a long time. This fact constrains the real opportunities that exist in the conductive coatings space.

Even where a sector of the market is inherently large, it is hardly an ‘opportunity,’ since the sector is likely to be adequately served by long-established suppliers.

The arrival of commercial nanomaterials in the past five or six years has opened up a new dimension of materials choice and, as we have seen, new business revenue potential.

Primarily because of the smaller particles involved, coatings, pastes and inks made with nanomaterials can be more conductive. In addition, metallic nanocoatings could potentially be thinner than other kinds of coatings, which could be important for some applications, especially when the materials are expensive or need to be highly flexible.

Finally, coatings based on nanomaterials may also dry faster because, for example, sintering temperatures decrease as the particle size decreases.