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Mass-Marketed OLEDs Could Power Lighting Revolution

Photonics.com
Apr 2007
BATH, England, April 19, 2007 -- A thin film of plastic that conducts electricity and produces solar power could be the basis for a revolution in the way we light our homes and design clothes. An international research project has begun that could help bring to mass-market organic LEDs (OLEDs), which could have far reaching technological implications and cut the cost of lighting by billions of dollars each year.

Because the devices are thin and flexible, lighting and electronic display screens could for the first time be created on almost any material, so that clothes and packaging can display electronic information. The devices' uses could vary from lighting that is many times more efficient than current bulbs to clothes that can easily change color and beer cans that display the latest football scores.
OLEDsDiversion.jpg
In this still image taken from animation, a policeman wears an OLED jacket on which warning information scrolls by in a manner similar to how electronic road warning signs work today. Because the devices are thin and flexible, lighting and electronic display screens could for the first time be created on almost any material, so that clothes and packaging can display electronic information. (Images courtesy of the University of Bath)
At present, the devices are used as displays in some mobile phones and MP3 players, but they are not reliable enough for larger screens such as in TVs and computers as they stop working after a few months. But now an international consortium of researchers, led by the University of Bath in England, has begun an £850,000 ($1.7 million), three-year project to help make OLEDs efficient enough to be worth mass-producing.

The consortium, called Modecom, consists of 13 groups from nine universities and two companies. Three groups are from the UK, six from the US, and one each from China, Belgium, Italy and Denmark. The European Union is funding the European and Chinese partners.

The devices exploit a discovery made around 15 years ago that some polymers have the unusual property of either turning electricity into light, or light into electricity, depending on how the devices are made. Because these polymers are thin and flexible, they could be used in a variety of ways:
  • As a transparent window. It would look like a conventional window during the day, but when it gets dark a switch is turned on and the entire window area emits light in a more efficient way than conventional or energy saving bulbs, promising huge savings.
  • In garments that could change color at the press of a button. Clothing could contain strips of the polymer powered by solar energy, allowing electronic messages to be displayed and easily updated. This could be useful for emergency services such as police or ambulance, in packaging goods and produce that could display electronic messages such as health warnings and recipes, or as a way to recharge mobile phone batteries. 
  • As lightweight, solar power sources that could be rolled up and stored, ideal for people requiring electricity in remote locations, such as field researchers, mountaineers, sailors and military personnel.
The consortium is coordinated by Alison Walker of the University of Bath's Department of Physics.

"The experimentalists make measurements to test the efficiency of the devices, but it's hard to get a clear picture of what is going on at present. This project is about making that picture clearer using computer models to develop the theory. Success in achieving the goals of cheap, efficient and long lasting devices is essential, as we must do everything we can to reduce our energy costs," Walker said. 
OLEDsFridge.jpg
An OLED warning appears on a yogurt container that has passed its expiration date. OLEDs could also be used on grocery items to display recipes. 
The polymer is made from chains of molecules, and is called organic because these contain carbon. Electrons and holes injected into the polymer film form bound states called excitons that break down under electrical current, emitting light as they do so.

Walker's part of the consortium's research uses a mathematical technique called Monte Carlo analysis, in which computer-generated random numbers are used to plot the paths of electrons, holes and excitons as they move across the film. The results can be used to calculate how the chemical structure and impurities affect the device's performance and then design more efficient materials.

The Modecom consortium will work on the molecular level and also look at the workings of the entire device. This research will also aid the understanding of the polymer materials used in plastic electronics in applications such as electronic paper and intelligent labels on groceries, the researchers said.

For more information, visit: www.bath.ac.uk


GLOSSARY
light
Electromagnetic radiation detectable by the eye, ranging in wavelength from about 400 to 750 nm. In photonic applications light can be considered to cover the nonvisible portion of the spectrum which includes the ultraviolet and the infrared.
photonics
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...
polymer
A material whose molecular structure consists of long chains made up by the repetition of many (usually thousands) of similar groups of atoms.
thin film
A thin layer of a substance deposited on an insulating base in a vacuum by a microelectronic process. Thin films are most commonly used for antireflection, achromatic beamsplitters, color filters, narrow passband filters, semitransparent mirrors, heat control filters, high reflectivity mirrors, polarizers and reflection filters.
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