New design for cheaper and more efficient white light LEDs

April 8th, 2009 - 5:48 pm ICT by ANI  

Washington, Apr 8 (ANI): In a bid to produce cheap and efficient white light for use in homes and offices, scientists at the Chinese Academy of Sciences have taken a major step towards developing a new type of light emitting diode (LED) made from inexpensive, plastic like organic materials.

Designed with a simplified “tandem” structure, the new LEDs can produce twice as much light as a normal LED, including the white light desired for home and office lighting.

“This work is important because it is the realization of rather high efficiency white emission by a tandem structure,” said Dongge Ma, who led the research.

Found in everything from brake lights to computer displays, LEDs are more environmentally friendly and much more efficient than other types of light bulbs, like incandescent bulbs and compact fluorescent bulbs, which waste much part of its energy as heat.

LEDs, on the other hand, are made from thin wafers of material flanked by electrodes and turn 20 to 50 percent, or even more, of the input energy into light. They also concentrate a lot of light in a small space.

While LEDs can easily be manufactured to produce light of a single colour — like red-with applications such as traffic lights and auto brake lights. But for indoor lighting, “natural” white light is needed.

This quality is measured by the colour-rendering index (CRI), which assigns a value based on the light source’s ability to reproduce the true colour of the object being lit. For reading light, a CRI value of 70 or more is optimal.

LEDs can produce white light by combining a mixture of blue, green, and red light, or by sending coloured light through a filter or a thin layer of phosphors-chemicals that glow with several colours when excited. But, these solutions increase costs.

Thus, to make inexpensive LEDs that can produce white light on their own, the researchers firstly built LEDs from organic, carbon-based materials, like plastic, rather than from more expensive semiconducting materials such as gallium, which also require more complicated manufacturing processes.

Then, they demonstrated, for the first time, an organic white-light LED operating within only a single active layer, rather than several sophisticated layers.

In fact, they even showed that by putting two of these single-layer LEDs together in a tandem unit, it was possible to achieve even higher efficiency.

The authors said that their LED could achieve a CRI rating of nearly 70-almost good enough to read by.

Progress in this area promises further reduction in the price of organic LEDs.

The study has been published in the latest issue of Journal of Applied Physics, published by the American Institute of Physics (AIP). (ANI)

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