Materials which change their colors when an electric field is applied to them are known as electrochromic materials. Displays using the materials (ECD) have a relatively long history of research and development. Many materials and device structures have been proposed but they had not succeeded in finding practical applications until very recently. Among the materials, a-WO
3 film has been studied most extensively and several products are available now.
Organic EC materials such as viologens were thought to have insufficient reliability but these materials have also improved considerably by adopting the polymer-type viologens or new materials such as styryl-like compounds.
These organic materials have the advantage of being able to displaying multi-colors. This will be very important for the future dot-matrix color ECD.
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