Criteria for Choosing Transparent Conductors
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Criteria for Choosing Transparent Conductors
Processes Used in Making Transparent Conducting Materials
Roy G. Gordon Introduction Transparent, electrically conductive films have been prepared from a wide variety of materials. These include semiconducting oxides of tin, indium, zinc, and cadmium, and metals such as silver, gold, and titanium nitride. In this article, the physical properties of these materials are reviewed and compared. A figure of merit for a transparent conductor may be defined as the ratio of the electrical conductivity to the optical absorption coefficient of the film. The materials having the highest figures of merit are fluorine-doped zinc oxide and cadmium stannate. Physical, chemical, and thermal durability; etchability; conductivity; plasma wavelength; work function; thickness; deposition temperature; uniformity; toxicity; and cost are other factors that may also influence the choice of transparent conducting material for any particular application.
Some Applications of Transparent Conductors Transparent conductors (TCs) have a wide variety of uses. Their ability to reflect thermal infrared heat is exploited to make energy-conserving windows. These lowemissivity (“low-e”) windows are the largest area of current use for TCs. Oven windows employ TCs to conserve energy and to maintain an outside temperature that makes them safe to touch. The electrical conductivity of TCs is exploited in front-surface electrodes for solar cells and flat-panel displays (FPDs). Automatically dimming rear-view mirrors for automobiles and electrically controlled “smart” windows incorporate a pair of TCs with an electrochromic (EC) material between them. Electric current is passed through TCs to defrost windows in vehicles and to keep freezer display cases frost-free. TCs dissipate static electricity from the windows on
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xerographic copiers. Glass touch-control panels are etched from TC layers. TCs can also be formed into transparent electromagnetic shields, invisible security circuits on windows, and transparent radio antennas built into automobile windows. It might appear reasonable to ask which transparent conducting material is the best. However, this question does not have a unique answer, since different TCs are best suited for different applications. Also, a given application may constrain the method of preparation and thereby affect
The properties of a TC layer depend not only on its chemical composition, but also on the method used for its preparation. These preparative methods include physical methods (sputtering, evaporation, pulsed laser deposition) and chemical methods (chemical vapor deposition, sol-gel, chemical bath deposition, electroplating). Some of the innovations in these deposition methods are listed in Table I. Spray pyrolysis was first used commercially more than half a century ago to deposit conductive tin oxide films on heated glass plates in batch processes. Since the 1980s, chemical vapor deposition (CVD) has been widely adopted in the continuous production of glass coated with fl
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