|Breakthrough Yields Brighter OLEDs|
|Post by Alex de Rafols|
|Thursday, 24 July 2008 21:02|
The future of LED lighting is looking bright. Endorsed by a $20M USD U.S. Department of Energy "L Prize", commercial powers and startups alike are eying LED lighting as a replacement for the decrepit incandescent light bulb technology, which is only 10 percent efficient and has remained almost unchanged for over half a century. Recent breakthroughs, which may allow LEDs of all kinds to be processed on silicon wafers, may help to bring down costs.
One player that remained largely unconsidered in the LED v. fluorescent/incandescent battle was LED's organic brethren: OLEDs. OLEDs have many advantages over LEDs -- the ability to flex, improved color, and the potential to be manufactured by cheaper organic ink printing processes. However, they also have a couple key disadvantages. One, lifetime, has been steadily chipped away, and with the first generation of OLED TV displays, the problem has become almost a nonissue. However, one key obstacle to OLED lighting remained -- brightness.
Typically with OLEDs, only 20 percent of the light generated by the device is emitted. This makes there brightness inferior to LEDs, making them a poor choice for lighting. However, in a significant breakthrough, researchers at the University of Michigan and Princeton University have developed an OLED/microlense combination material that boosts illumination by over 60 percent, bringing it into the realm of respectability.
The research was led by Stephen Forrest, a professor of electrical engineering and physics at Michigan, and Yuri Sun, from Princeton University. The pair observed that in OLEDs light is generated by applying electricity to a thin organic layer, analogous to the semiconductor in an LED. However in OLEDs the material character internally reflects the light, forcing it to run parallel, instead of perpendicularly out of the bulb.
To get the light to come out, researchers first use an organic grid meshed into the material. The light is guided by this grid to 5 micrometer domed microlenses, which focus it and project it out as rays.
The results are respectable. The researchers reported that the device produced 70 lumens per watt, compared with 15 lumens per watt for incandescent lighting, and 90 lumens per watt for fluorescent lighting. While it might seem that fluorescent beats the new OLEDs, fluorescent has other problems -- harsh light, less longevity, and the use of environment-damaging substances like mercury.
The team plans to next scale the technology to more efficient OLED designs. They are confident the process can be affordably adopted for mass commercial production.
The DOE is curious about the new technology, seeing as a way to possibly more affordably reach its LED adoption goals. If LEDs are widely adopted, according to the DOE, U.S. energy consumption for lighting could be cut to a third of current levels, resulting in a 10 percent total reduction in power use and a 258 million metric ton reduction in carbon emissions.
As both LED and OLED technologies are rapidly advancing in terms of production and efficiencies, it remains to be seen which will ultimately prove themselves the eventual victor via performance and cost. However, in Professor Forrest's eyes, the future of OLEDs has never looked better. He is confident that OLEDs will thrive, and that his team's breakthrough will aid in that success. He states optimistically, "Luckily, OLEDs are the light that just keeps giving. There is so much to be done and so much that's been done, but this is nonetheless a quite exciting advancement."