OEL displays add color with polymer technology

In fewer than six years of development, says David Mently, vice president of market-research firm Stanford Resources (San Jose, CA), commercial activity in the organic electroluminescent (OEL) community is now exploding. After Eastman Kodak (Rochester, NY) and Sanyo (San Diego, CA) unveiled a full-color OEL display at last year's Japan Electronics Show, Seiko Epson ...

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In fewer than six years of development, says David Mently, vice president of market-research firm Stanford Resources (San Jose, CA), commercial activity in the organic electroluminescent (OEL) community is now exploding. After Eastman Kodak (Rochester, NY) and Sanyo (San Diego, CA) unveiled a full-color OEL display at last year's Japan Electronics Show, Seiko Epson (Long Beach, CA) and Cambridge Display Technology Ltd. (CDT; Cambridge, England) developed a full-color display using CDT's light-emitting-polymer (LEP) technology.

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Resulting from a joint development between Cambridge Display Technology and Seiko-Epson, this monochrome television display features 800 x 236 pixels and measures 45 x 37 mm. (Image copyright CDT Ltd. Wallace and Gromit characters are courtesy of Aardman Animations; Gasferry Road, Bristol, England.)
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This latest development follows CDT's initial announcement two years ago that it had demonstrated a monochrome plastic TV display based on LEP technology. That display used light-emitting polymers to create a display that measured 45 x 37 mm and could display images as large as 800 x 236 pixels. According to the company, the new prototype color display measures 2.5 in. square and provides 200 x 150-pixel resolution.

In the display developed by Kodak, the basic OEL cell structure consists of a stack of thin organic layers sandwiched between a transparent anode and a metallic cathode. The organic layers comprise a hole injection layer, a hole-transport layer, an emissive layer, and an electron-transport layer. When a voltage is applied to the cell, the injected positive and negative charges recombine in the emissive layer to produce light. The structure of the organic layers and the choice of anode and cathode are designed to maximize the recombination process in the emissive layer, thus maximizing the output light from the device.

An OEL display consists of thin layers of individual carbon-based elements that emit light when electric current is applied. Each element, or pixel, can be turned on or off independently, and can create multiple colors; OEL displays require no backlight and consume low power.

CDT and Seiko-Epson are initially targeting the technology at portable electronic devices.

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