Uses of alt-TCOs as Transparent Conductors
Published: September 26, 2011 Category: Advanced Materials

Forms of zinc and tin oxide have been proposed as an alternative to indium tin oxide (ITO) in the display and PV industry for many years, with mixed commercial success.  In the thin-film PV (TFPV) space, alternative TCOs (alt-TCOs) have done well with fluorine tin oxide (FTO) and aluminum zinc oxide (AZO) becoming quite common at this point in time.  However, attempts to sell indium zinc oxide (IZO) into the display space have not succeeded to any strong degree.

The motivation for using alt-TCOs is usually that money can be saved on materials, and  most often because large amounts of indium can be avoided.  This matter has taken on a new urgency in view of recent Chinese industrial and trade policy, which favors controls on exports of indium.  The Chinese government has also shut down environmentally unsound indium extraction facilities.  The potential opportunities for alt-TCOs seem to 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.
Adding to the fun are new applications for alt-TCOs and the emergence of new kinds of TCOs.  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 many years, but may well emerge as a mass market product if the green building movement continues to fulfill it's promise.

Finally, with the help of a semantic stretch, one might consider the use of the metal oxide materials considered in this report in thin-film transistors (TFTs) as part of the opportunity space for alt-TCs.  Here one is, in effect, saying that a transparent conducting oxide is also a semiconducting transparent oxide.  Taken literally, these statements are simply a contradiction in terms. However, given that these alt-TCOs are neither very conductive nor very semi-conductive, we hope that the reader will forgive our embracing of this contradiction.  We should perhaps mention that some of the most interesting new alt-TCOs are emerging in the context of TFTs.

The Joys and Otherwise of Sputtering

While such new applications are certainly the most interesting from a purely intellectual point of view, and we think may also turn out to be the most profitable opportunities for alt-TCOs in the end, they are certainly also the most risky.  It also seems likely that they will take quite a while before they generate significant revenues.

Given the extraordinarily difficult business climate that pertains at the present time, it seems that many makers of alt-TCOs will be looking for more immediate and less risky opportunities.  The least risky of these opportunities is certainly in the TFPV space, where suppliers of AZO and CIGS can simply expect to see sales rise as CIGS and CdTe continue to experience growing revenues.  This application is a low risk opportunity in that all the alt-TCO has to do is follow the TFPV industry onwards and upwards.

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