Nanotechnology innovation promises cheaper, clearer LEDs

September 25, 2014 // Paul Buckley

Princeton University researchers have developed a new method of increasing the brightness, efficiency and clarity of LEDs used on smartphones and portable electronics as well as for lighting applications.

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The method also claims to improve the picture clarity of LED displays by 400 percent, compared with conventional approaches. In an article published online in the journal Advanced Functional Materials, the researchers described how they accomplished the performance improvements by inventing a technique that manipulates light on a scale smaller than a single wavelength.

"New nanotechnology can change the rules of the ways we manipulate light," said Chou, who has been working in the field for 30 years. "We can use this to make devices with unprecedented performance."

Current LEDs have design challenges; foremost among them is to reduce the amount of light that gets trapped inside the LED's structure. Although they are known for their efficiency, only a small amount of light generated inside an LED actually escapes.

"It is exactly the same reason that lighting installed inside a swimming pool seems dim from outside because the water traps the light," said Chou, the Joseph C. Elgin Professor of Engineering. "The solid structure of a LED traps far more light than the pool's water."

In fact, a rudimentary LED emits only about two to four percent of the light it generates. The trapped light not only makes the LEDs dim and energy inefficient, it also makes them short-lived because the trapped light heats the LED, which greatly reduces its lifespan.

"A holy grail in today's LED manufacturing is light extraction," Chou said.

Engineers have been working on this problem. By adding metal reflectors, lenses or other structures, they can increase the light extraction of LEDs. For conventional high-end, organic LEDs, these techniques can increase light extraction to about 38 percent. But these light-extraction techniques cause the display to reflect ambient light, which reduces contrast and makes the image seem hazy.

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Nanotechnology innovation promises cheaper, clearer LEDs

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