Alternatives to ITO for Transparent Conductors

By AZoM

Table of Contents

Introduction
The Joys and Otherwise of Sputtering
The New TCO Palette
New Alt-TCOs, New Applications, New Companies
About Nanomarkets

Introduction

Forms of zinc and tin oxide have been suggested as an alternative to indium tin oxide (ITO) in the PV and display industry for many years, with mixed commercial success. In the thin-film PV (TFPV) space, alternative TCOs (alt-TCOs) have excelled with fluorine tin oxide (FTO) and aluminum zinc oxide (AZO) being quite common at this point in time. However, attempts to sell indium zinc oxide (IZO) into the display space has not succeeded to any strong degree. The potential opportunities for alt-TCOs have grown as a result, although these TCOs also now have to compete increasingly with next-generation transparent conductors that will almost certainly outperform them given time. One new application that we see as being of considerable importance for these materials is so-called smart windows. Such windows have enjoyed niche status for several years, but may well emerge as a mass market product if the green building movement continues to fulfill it's promise.

The Joys and Otherwise of Sputtering

Alt-TCOs, however, can only substitute for ITO when their performance is good enough, and the choice of an alt-TCO may be for quite simple reasons. For example, First Solar, which dominates the CdTe panel market, adopted FTO for a transparent electrode due to the convenience with which it could be applied to glass. Alt-TCOs are advantageous mainly due to their cost. The alt-TCO uses a less costly metal than indium or at least less indium than ITO. But the real unique claim for alt- TCOs is that they continue to use sputtering and therefore minimize economic switching costs for firms that adopt TCOs, even though switching costs are never zero.

One must note that in any existing operation that already uses ITO, production scale sputtering equipment is already present and often depreciated or even fully depreciated. Furthermore, at such production plants, the sputtering process and its controls are understood. Any novel material will have a much higher likelihood of success if it can be used with existing production equipment and this scenario is the case with alt-TCOs. While printing and solution deposition are the vision of the newer transparent conductors (TCs) that use nanomaterials or polymers, the truth is that no sane manufacturing facility will adopt a new TC technology unless it brings them 30-50% savings in manufacturing cost reduction or the current manufacturing practices cannot offer the products that an organization has targeted.

The use of existing sputtering facilities is hence a key competitive advantage that alt-TCOs have over all other replacements where alt-TCOs are being considered for existing operations. It must be understood that economic switching costs cannot be avoided entirely.

The New TCO Palette

The alt-TCOs and the applications mentioned are well established and the impact of Chinese indium policy seems certain to be a key driver for alt-TCOs going forward. Indeed, in case the tsunami never happened, which led to low production in Japanese display firms, there may have been an ITO shortage in Japan at the beginning of 2011. It seems likely that this problem has only been put off and will result in alt-TCOs receiving more attention by the year 2012.

Of course, in time the indium market will adjust to any likely supply restrictions imposed by the Chinese authorities, although it may take several years for this development to happen. In addition, alt-TCO suppliers that are attacking the ITO replacement market face growing competition from nanomaterials that are likely to exceed them in terms of performance in the near future and are also inherently flexible, something that TCOs are not. With flexible displays and PV panels now moving towards commercialization, the lack of flexibility is something that works against the expansion of the alt-TCO market.

The uncertainties associated with ITO replacement by alt-TCOs are restricted when compared to the risks associated with creating and marketing new alt-TCOs. Here we find significant and novel risks at the level of the materials themselves in terms of the applications and also in terms of business structure and leadership.

New Alt-TCOs, New Applications, New Companies

Latest research asserts that there exists a “sweet spot” on the periodic table where one can find the elements that have the highest figure of merit for effective alt-TCOs. Unfortunately, this approach includes some very bad elements such as cadmium and mercury. But excluding them, there remains a mind-boggling amount of opportunity space to explore for both old and new applications.

Obviously, the creation of alt-TCOs can be directed toward older applications, most notably ITO replacement. It is also possible that these newer materials will be used for newer applications:

  • A main goal for TCO innovators is the development of robust p-type semiconductors. Most TCOs are n-type semiconductors (e.g., ITO). However, considerable effort is devoted to developing p-type semiconductors that will lead to needed innovations such as robust transparent thin-film transistors (TTFTs). Copper based p-type TCOs are already known.
  • Several companies including Sony, Sharp and Toshiba have demonstrated AM-OLED displays with transparent TFTs of amorphous Indium-Gallium-Zinc-Oxide (IGZO).
  • There is now considerable interest in transparent displays that will either use OLEDs or quantum dots (QDs) as their core technology. These displays will need transparent TFTs, with amorphous multi-component TCOs based on IZO being the most likely alt-TCO to be used in this context. Samsung built a QD-based prototype display using TFTs made from the alt-TCO amorphous hafnium-indium-zinc oxide (HIZO).
  • There may be new applications for alt-TCOs in smart windows.

The risks of these novel applications are only compounded by likely changes in business structure. IZO was evaluated by Samsung as a transparent conductor because it was much easier to etch than crystalline ITO and could stand up to plasma processing. At one time, there was talk that IZO may take as much as 30 % of the display market, but that never happened. One reason seems to be the fact that Idemitsu Kosan holds significant patents governing the use of IZO. This IP factor adds to the already high price of this the material; after all, ITO and IZO have almost the same amount of indium, so it is not possible to realize any material savings. The process savings do not outweigh the cost factors and hence this material is in decline.

However there may be some good news for IZO. It appears that IZO has evolved into the amorphous TCO space like HIZO as mentioned above. What was originally seen as an anode application has found a new niche in oxide transistors.

Many of the newer TCOs are going to be dependent on IP from companies in much the same way as is indicated for IZO. The Pricing strategy, therefore, is likely to be an important factor for firms in the alt-TCO market of the future in a way that is not the case for the present class of TCO firms who operate in a much more commoditized space.

About Nanomarkets

NanoMarkets is a leading provider of market research and industry analysis of opportunities within advanced materials and emerging energy and electronics markets. Since the firm’s founding, NanoMarkets has published over one hundred comprehensive research reports on emerging technology markets. Topics covered have included OLED displays, lighting and materials, thin-film electronics, conductive inks, transparent conductors, renewable energy, printed electronics and other promising technologies. Our client roster is a who’s who of companies in specialty chemicals, materials, electronics applications and manufacturing.

This information has been sourced, reviewed and adapted from materials provided by NanoMarkets.

For more information on this source, please visit NanoMarkets.

Date Added: Dec 1, 2011 | Updated: Jun 11, 2013
Ask A Question

Do you have a question you'd like to ask regarding this article?

Leave your feedback
Submit