|
Wednesday, July 23, 2008 More-Efficient OLED LightingResearchers have found a way to boost light from OLEDs. By Lee Bruno
Energy efficiency and flexible lighting applications have long been the promise of organic light emitting diodes (OLEDs). The technology hasn't lived up to its promise, however, because in typical OLEDs, only 20 percent of the light generated is released from the device. That means that most light is trapped inside the bulb, making it highly inefficient. Researchers at the University of Michigan and Princeton University believe that they're on to a way to break the OLED-efficiency logjam. The scientists have designed an OLED that boosts illumination by 60 percent using a combination of an organic grid working in tandem with small micro lenses that guide the trapped light out of the device. Stephen Forrest, a professor of electrical engineering and physics at Michigan, and Yuri Sun, from Princeton University, described the work in the August issue of Nature Photonics. In OLEDs, white light is generated by using electricity to send an electron into nanometer-thick layers of organic materials that behave like semiconductor materials. Typically, the light in the substrate is internally reflected and runs parallel and not perpendicular. That's the crux of the problem because the light can't escape in the vertical direction without some coaxing. In Forrest's devices, the grids refract the trapped light, sending it to the five micrometers dome-shaped micro lenses. The light is sent off in a vertical orientation that helps release the trapped rays. Forrest and his coworkers report that the technology emits about 70 lumens from a watt of power. In comparison, incandescent lightbulbs emit 15 lumens per watt. Fluorescent lights put out roughly 90 lumens of light per watt but have liabilities: they produce harsh light, lack longevity, and use environment-damaging substances like mercury. Forrest says that the next step in the research is to use OLEDs that are more efficient than those the team used in the current project. Looking beyond the research lab work on these OLEDs, he is cautiously optimistic that it should be possible to scale up the manufacturing of the devices, and that production costs for manufacturing the new OLEDs will be competitive. Today, an estimated 22 percent of the electricity produced goes to lighting buildings. A highly efficient form of OLED lighting could significantly reduce the electricity demand and boost savings. Another factor influencing broad adoption of LEDs is the fact that they outlast incandescent bulbs. Over the next 20 years, the rapid adoption of LED lighting in the United States could reduce electricity demands by 62 percent and thus eliminate 258 million metric tons of carbon emissions, according to the Department of Energy. It will take several years to replace current lighting in office buildings and homes with OLEDs. But the continued progress in increasing the efficiencies of the devices is encouraging to researchers. "Luckily, OLEDs are the light that just keeps giving," says Forrest, who has spent much of his professional research career focused on OLEDs. "There is so much to be done and so much that's been done, but this is nonetheless a quite exciting advancement." |
Audio »
Share »
Digg this
Add to del.icio.us
Add to Reddit
Add to Facebook
Slashdot It!
Stumble It!
Add to Newsvine
Add to Connotea
Add to CiteUlike
Add to Furl
Googlize this
Add to Rojo
Add to MyWeb
Favorite
Print
E-mail
See-Through Transistors
06/04/2007
Comments
erik1974 on 07/23/2008 at 1:29 AM
4
Check out this site:
http://www.oled-display.net
hachi on 07/23/2008 at 4:11 AM
21
Ha. The harsh light joke is a myth, I'm sitting here right now, and the light is as warm as incandescent ever was. Lacking longevity, yes, in relation to a LED or OLED, but compared to a incandescent they last way longer.
Siphon on 07/26/2008 at 6:10 AM
93
mercury fact sheet
It's typical behaviour from people who like technology x to make their product look better by talking down on product y.
This is absolutely unneeded. Both CFLs and (O)LED are excellent technologies to save big on lighting energy.
Besides, there's new CFLs under development that are even more efficient and contain no mercury. Technology alone may not be able to save us, but it does move ahead, and it's important to recognize this fact, lest we be stuck in propaganda.
amgillard on 07/23/2008 at 10:22 AM
7
"... Typically, the light in the substrate is internally reflected and runs parallel and not perpendicular" to the surface of the OLED by turning the OLED cell up on its edge ?
The light could then be directed up and out from the substrate layer by ensuring it has a clean, smooth top edge at right angles to the surface - internal reflection will only work at high angles of incidence (close to parallel with the surface), and hence the light will be emitted through the edge layer of the substrate.
It would complicate fabrication, but a control grid could be laid down first, then the OLED cells positioned over the grid to allow for addressing control.
The other edges could even be coated to promote the internal reflection of the light except for through the top edge.
jsessex on 07/23/2008 at 7:42 PM
12
Woody007 on 07/25/2008 at 10:03 AM
1
ralphw on 07/28/2008 at 4:06 PM
2
How does this compare to the high-intensity LED I've been hearing about?