Transparent conductive films: a step behind the technology curve?

Transparent conductive films (TCFs), an alternative to indium tin oxode (ITO) for use in displays, are no longer a young technology. They have been in semi-commercial mode for more than a decade and half. In that time, they have often come tantalisingly close to success and, in some instances, even carved out niche markets. Yet they are still hoping for that great breakthrough. So why has the commercialisation process been prolonged for so long?

Flexible displays: market success for ITO alternatives?

The primary market for TCFs is touch displays and a major trend in the display industry has been the rise of robust, flexible and rollable screens. This technology frontier has been in the making for many years and it is now finally on the cusp of commercial success. This is because the different pieces of the puzzle are finally fitting together: rigid plastic OLED displays have been on the market since around 2014 and now both the thin film encapsulation technology and LTPS (or other backplane tech) on PI are becoming increasingly flexible (not just plastic based).

This trend towards flexibility has long been considered as the ultimate panacea for ITO alternatives, since ITO films fail if bent too much and/or too many times. Indeed, it is this prospect that has long motivated large swathes of the industry for years. So, now that we are so close to commercialisation of flexible OLED displays, why is there no unrestrained euphoria?

The answer is that industry is now concerned they will turn out just to be a temporary solution — a mere placeholder until an ultrathin embedded solution is readied when the right production yield is achieved.

Rigid plastic displays mainly utilise ITO films. This limited flexibility therefore needs to give way to a flexible alternative. Therefore, many are exploring the use of ITO alternative films, all of which are flexible. Here, these alternative films compete on performance (sheet resistance, transparency, haze, etc), degree of flexibility and cost. Currently, the likely leading winners include Ag nanowires and even some metal mesh films.

There are, however, already clear indications that film-based add-on implementation will not be the end game. This is because embedded in-house-made flexible touch sensors are already demonstrated by several display makers. In fact, a version is already commercialised by a leading OLED display producer.

In the embedded implementation, the display makers manufacture the touch layers on the conformal multilayer top barrier. The touch sensor is deposited using tools such as evaporation and sputtering, and is made up of metals such as TiOx. It is thus a form of embedded in-house-made metal mesh, but not metal mesh film.

This technology requires expertise (thus an extensive in-house learning curve) and the allocation of expensive in-house assets to touchscreen production. It also requires careful process control so as not to damage the underlying encapsulation layer. In addition to production complexity, its commercial spread to more display makers might also be hampered by IP issues.

This embedded technology, however, will likely win on one key attribute: thinness, which also determines the degree of flexibility. It achieves such thinness especially by eliminating the transparent conductive film and the adhesives (ie, TCF and OCA). It can also be further thinned by interweaving the touch structure with the inline thin film encapsulation layers. This approach is not yet commercial, but patent trends suggest it is of active interest.

Consequently, flexible TCF films risk being cut out of the market if the technology transitions from add-on to embedded touch in flexible displays. Note that a similar transition has already taken place in rigid LCD displays, adversely affecting the market for film supply. The main losers of such technology shifts have been the film makers and touch integrators.

What to do?

These transitions are nothing new for the touch screen, which throughout its history has had to contend with rapid and significant technology changes. Indeed, the industry knows that it must make hay when the sun shines as every few quarters there might be major technology transitions. In the short term, the transition towards flexibility displays will bring benefits — in terms of new touch technologies and integration/laminations expertise — but in the long term the road will be more turbulent.

In any case, however, it will be more probable that we will witness a long and gradual transition towards true embedded integration. During this process, there will be a varied technology mix, keeping the market open for ITO alternative films. This will be the case because not every company will have the expertise and/or the legal right to do true embedded implementation, while add-ons will find ways to stay competitive by offering a better cost position and just-about-enough performance for displays not requiring low bending radiuses.

The various makers will need to offer multiple-function-in-one TCFs, meaning that the TCF could be combined with colour filters, polarisers or barrier films, thus saving thinness. In the longer term, various transparent conducting technologies may adopt to changing trends. In particular, materials (not films) such as silver nanowires might be used in the in-house embedded process if they are conformal, ultrathin, high performance and can be easily photopatterned, or if various technologies can be directly printed on the barrier structure. This indeed is essentially what has happened to metal mesh in current embedded on-TFE touch. This development might allow these technologies to stay relevant but will require further R&D.

Beyond displays: breaking out of purgatory?

At the start we mentioned that TCF technologies are out of synch with technology development. In the case of flexible displays, they might have to forever play catch-up. In case of other addressable markets, however, the waiting game goes on.

Take flexible organic photovoltaics (OPVs) and flexible OLED lighting as examples. Both technologies need flexibility to differentiate and to be commercialised. As such, they will likely eventually need ITO alternatives. In the case of OPV, companies are finally selling parts of their narrow-web R2R solution processing capacity with some contemplating a transition to wide web production. In the case of OLED lighting, some producers have transitioned to S2S Gen5 production while investment in wide-web R2R production was also made some years ago. Despite this progress, the challenge is that both OPVs and OLED lighting remain underperforming and overpriced compared to the incumbent Si PV and inorganic LED lighting. As such, there is still much work to do to bring commercial success and thus the wait for all device component suppliers — including TCFs — goes on.

Consequently, TCFs are caught in a purgatory when it comes to these applications. They cannot leave the space because every opportunity is important to the industry and they are unable to proceed because the end market is not quite commercially ready. The waiting game, therefore, will go on in the short to medium term. However, we believe that these and similar applications will arrive. Indeed, we estimate that emerging applications (vs those established today) will come to represent more than 50% of the market in 2028 (up from <10% today).

The IDTechEx Research report ‘Transparent Conductive Films and Materials 2018-–2028: Forecasts, Technologies, Players’ provides a detailed technology assessment for all established and emerging transparent conductor layer technologies. It also offers 10-year market forecasts segmented by 20 applications and 10 technologies, covering more than 90 companies in the field. For more, see www.IDTechEx.com/TCF.

Image credit: ©stock.adobe.com/au/photographee2000

Originally published here.