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Technology

New multistate display can be sign, mirror or window

Light shines from the overlay of two display types.   © Courtesy of Takayuki Uchida

TOKYO -- A Japanese university team has developed what may be the world's most versatile display, capable of easily switching between transparent, black, light-emitting or reflective.

     The device is a combination of two display technologies layered on top of each other. One is an electromechanical display made up of transparent electrodes, while the other is an organic electroluminescent display of the sort used in cellphones.

     Its versatile nature means a wide range of potential applications. Used as a house window, for example, the display could regulate incoming sunlight during the day to reduce heating and cooling costs or light the interior at night. Professor Takayuki Uchida and his team at the Tokyo Polytechnic University, with business partners, are hoping for commercialization within a few years.

A reflective transparent electrochemical device made using the spray CVD technique   © Courtesy of Takayuki Uchida

Altered states

The display changes states -- switching colors or turning transparent, for example -- depending on the electrical charge.

     The organic electrochemical layer shifts among three states, transparent, black or reflective, while the organic electroluminescent layer shifts between two, transparent and light-emitting. These states can be combined in various ways to offer even more display options, such as light-emitting on both sides or light-emitting on one side and reflective on the other.

     The transparent electrochemical layer consists of electrodes made of tin-doped indium oxide and a solution of silver ions sandwiched between two glass plates. One type of electrode has a flat surface, the other a rough one. When a charge lines up the silver particles on the smooth surface, the display becomes reflective, and when the charge changes polarity and moves the silver to the rough surface, the diffusion turns the display black. With no electric charge, the display is transparent.

     The potential for energy savings is high. The device can reflect sunlight, raising the efficiency of air-conditioning systems in summer, while during winter it can turn black to help retain warmth in a room. Applied as outdoor electronic signage, it can shift to the optimum display for the given weather and time of day.

     Uchida's team has produced a 15-by-15cm prototype estimated to cost about 5,000 yen ($48) for the electrochemical side and about 10,000 yen for the electroluminescent side. The target price for the finished product is a few thousand yen per square meter.

     The team has already developed technology that produces larger displays more easily than conventional methods. It uses the CVD (chemical vapor deposition) spray technique, used to make fine films, to control the diameter of the crystallized transparent electrode particles, replacing the disk-shaped devices often used in semiconductor production. The focus now is on improving performance factors, such as responsiveness and durability.

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