PLEDs Aim to Improve Picture, Price Tag of Plasma

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Single-layer, inexpensive plastic LEDs are being developed that could make the next generation of flat-panel TVs brighter, clearer and less expensive. The record-breaking research will be presented at the Society for Information Display (SID) 2007 conference in Long Beach, Calif., from May 20-25.

Most people probably don’t think much about the inner workings of LEDs, or light-emitting diodes, which illuminate today’s plasma TV screens and cell phones, but making these LEDs more efficient, cheaper and higher quality is the obsession of University of California, Los Angeles materials science and engineering professor Yang Yang and his graduate researcher Jinsong Huang, both researchers at the Henry Samueli School of Engineering and Applied Science.LEDEngineers.jpg
UCLA Engineering researcher Jinsong Huang (left) and Professor Yang Yang are striving to improve LEDs, work that could lead to flat-panel televisions having clearer, brighter pictures and lower price tags. (Image courtesy UCLA Engineering/R.Hutchinson)
Yang and Huang have recently achieved the highest lumens per watt ever recorded for a red phosphorescent LED using a new combination of plastic, or polymer, infused liquid -- and for half the current cost.

“That means your next LED flat-panel TV could be less expensive,” Yang said. “And the picture will be brighter and clearer than ever before.”

LEDs are generally measured in lumens per watt (lpW). Lumens, a measure of the perceived power of light, and watts, a standard measure of power, combine to define the optical efficiency of power -- in other words, how bright a device is and how much power it consumes.

Current red LEDs generally score around 12 lpW. Yang and Huang’s newest device breaks the record at 18 lpW.

“That’s a significant difference,” Huang said. “Visually, it means you get a higher quality display, and the product is also lighter and thinner. And with our improvements, you also need less energy, but you get an all-around better product.”

Conventional organic LEDs are made from a variety of organic semiconductor materials and have a complicated multiple-layer structure formed by expensive thermal evaporation techniques constructed to control charge flow in the device. LCD televisions, for example, require polarization, color filters and other components to make the resulting picture clear and bright.  The more you build into a product, Yang said, the more energy it takes to run it, and the bigger it is.  LCD TVs have also begun to add LEDs as backlights to improve picture quality and power consumption.

In Yang and Huang’s new polymer LEDs, the devices have a very simple single-layer structure, generated by a much cheaper solution process. The new LED, or more precisely PLED, uses a polymer powder and liquid mixture added to a previously top-secret material developed by Canon Inc. to create a paint-like product. The product is used to coat a layer of glass, and a charge is added. The end result is a slim single layer of glass with two electrodes.

“It’s a much simpler, lighter, thinner and more elegant answer to creating a better LED product,” Yang said.

Yang began his PLED research at UCLA Engineering in early 2003 with a then-graduate student named Qianfei Xu, who was part of the professor’s research group, and achieved a record-high efficiency for green PLEDs.

“The current results represent our ongoing quest to create better, slimmer, less expensive high-performance PLEDs,” Yang said. “Using our simple solution method, we already have successfully achieved several world records in device efficiency, including 20 lumens per watt white-emission fluorescent PLEDs, 30 lumens per watt green-emission fluorescent PLEDs and 18 lumens per watt red-emission phosphorescent PLEDs. So our latest red-emission PLED is just one of our multiple records. It’s a very exciting development.”

The technology, which has been licensed by Canon, should be available to consumers in about three years, the researchers said.

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Published: May 2007
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
A gas made up of electrons and ions.
Polymers are large molecules composed of repeating structural units called monomers. These monomers are chemically bonded together to form long chains or networks, creating a macromolecular structure. The process of linking monomers together is known as polymerization. Polymers can be classified into several categories based on their structure, properties, and mode of synthesis. Some common types of polymers include: Synthetic polymers: These are human-made polymers produced through...
Canonflat-panelfluorescentHuangJinsong HuangLCDLight SourceslumensNews & FeaturesphosphorescentphotonicsplasmaPLEDPLEDspolymerred-emissionsemiconductorsSIDTVUCLAUCLA EngineeringYangYang YangLEDs

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