Saif Haque

Light exits the new organic LED.
Titanium-dioxide spheres, coated with a light-emitting polymer (orange), sit between glass (left) and gold contacts.

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You can't buy a television that you can roll up and tuck into your pocket, even though much of the technology exists to make flexible video displays based on organic light emitting diodes. That could soon change, according to researchers who have tinkered with the formula to boost the flexibility of a key component.

Organic LEDs are a promising alternative to other solid-state or plasma display technologies. They use less energy because they do not require backlighting, and they are easier and cheaper to manufacture. The conventional design employs two flat electrodes with a layer of light-emitting organic molecules between them. Until now, one of the electrodes was usually made from an unstable, reactive metal, limiting the lifetime of the devices. Encapsulating the electrode in plastics or epoxies helps protect it from degrading in air, but a hard coating reduces flexibility.

Researchers at Imperial College London were able to make organic LEDs without any encapsulation layer by replacing the unstable metal electrode with nanostructured titanium dioxide, a highly porous material that is a common ingredient in whitewash and toothpaste. Although titanium dioxide has proven its mettle for years in solar cells, this is the first time it has been employed in LEDs. The resulting spongy surface provides 1000-times more area for the light-emitting molecules than does a traditional flat electrode. Fine-tuned designs could produce more light, for longer, at lower voltage, says Saif Haque, lead author of the study published online last week in Advanced Materials. Eventually, titanium dioxide could remove the need for encapsulation altogether, improving the flexibility of future devices without sacrificing lifespan.

"It's a timely and smart assimilation of ideas from different fields," says physicist Richard Friend of the University of Cambridge in the U.K. But he cautions that researchers need to demonstrate that the designs are more efficient before they will be viable for applications. But if that work pans out, it could make for displays that would fit in your pocket but don't drain your pocketbook.

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