Let There Be (a New Kind of) Light
Organic LEDs seem set to transform the business of bulbs
Photo: Makoto Ishida
Soft Light: Junji Kido of Yamagata University shows off his bright and smooth prototype OLED system.
Recent events on the business front and advances in the lab could soon transform the way we go about lighting our homes and buildings. Significant strides in developing organic light-emitting diodes (OLEDs) may allow architects in the next few years to integrate this power-efficient and tractable technology into basic building materials, enabling entire structures to be turned into luminous edifices. In the home, sheets of this next-generation lighting material might be applied like wallpaper for illumination purposes and to provide changing background hues to suit particular moods; further development of the material could see it double as wall displays and televisions.
This March, Konica Minolta Holdings, a Tokyo-based manufacturer of imaging products, and General Electric Co., one of the world's largest lightbulb makers, formed a strategic alliance to accelerate development of OLED lighting and vowed to ship products in the next three years. Meanwhile, as researchers around the world race to commercialize OLED lighting, an engineering group at Yamagata University in northeast Japan says OLED lighting products based on its work will be launched as early as next year.
With no need for backlighting, the technology has already been used to produce low-powered small displays for mobile digital products such as cellular phones. And a few months ago, Tokyo-based Sony Corp. announced it would ship an 11-inch OLED TV this year.
A typical OLED lighting structure is composed of films of organic compounds and conductive layers sandwiched between two electrodes that provide positive and negative charges. When the two charges recombine in the organic layer, energy is given off in the form of photons, creating a patch of soft visible light. In theory, the efficiency of this energy conversion could reach 100 percent, researchers say.
Such a structure (excluding the substrate) has a depth that can be measured in mere nanometers, making for extremely thin, lightweight lighting products (and displays) that could be manufactured in sheet form. This opens the way for large area lighting and differentiates the OLED from its cousin, the light-emitting diode, or LED—a device designed to be a point light source.
In the lab, at least, OLED material can be put on a variety of substrates, including flexible plastic. The material also is environmentally friendly, containing no harmful elements such as the mercury found in fluorescent tubes.
Junji Kido, a professor in the department of organic device engineering at Yamagata University, has been working on OLED developments for some 19 years and was the first to introduce a white OLED light in 1993. His research team has more recently demonstrated prototype OLED lighting that produced 5000 candelas per square meter with an efficiency of around 20 lumens per watt —four times better than a 100-watt incandescent bulb.
The prototype OLED lighting uses fluorescent-based material, which is less efficient than phosphorescent OLED compounds, allowing great room for improvement. ”We are now introducing phosphorescent [materials] and can bring up the lumen efficiency to 40 or 50 lm/W very easily,” says Kido.
Such is their progress that Kido says the university is forming a joint venture ”with four or five companies” and plans to launch OLED lighting products in 2008.
Elsewhere, in June 2006 Konica Minolta announced the development of a white OLED light panel with an industry-record power-efficiency of 64 lm/W at 1000 cd/m2—four times as efficient as incandescent bulbs. This was achieved following KM's earlier development of a blue phosphorescent OLED material with a decent lifetime—the missing ingredient needed for combining with red and green OLED phosphors to create efficient white light suitable for commercialization.
”Until we developed this blue phosphorescent material, there was no such material with a good lifetime,” says Tawara Komamura, general manager of R&D display technology at the Konica Minolta Technology Center, the research arm of KM. Whereas red and green phosphor OLED materials have been available, notably from Universal Display Corp., based in Ewing, N.J., ”blue phosphor was a challenge to develop, just as it was with LEDs,” says Komamura.
Since then, KM has pushed the lumen efficiency up to 70 and extended the lifetime of the material to beyond 10 000 hours. GE has also been making progress in the lab, and the two companies say that by combining their resources they can bring OLED lighting to the market by 2010.
However, competitor Kido, donning his professorial hat, says the KMGE announcement raises a number of questions. ”The luminance required for general lighting is between 3000 to 5000 cd/m2,” says Kido. ”So improvement is still needed in Konica Minolta's 1000 cd/m2 [system], though it may be good for displays.” Usually, he points out, the luminance efficiency decreases when the brightness goes up.
KM argues that for certain types of lighting 1000 candelas is sufficient, especially when incorporating the high luminance efficiency that KM has achieved.
A major challenge all OLED manufacturers face is how to make their products cost-competitive with the ultracheap incandescent and fluorescent lighting products on the market.
”Cost will be key to penetrating the marketplace,” agrees Toyohito Tanaka, general manager and head of business development in Konica Minolta Holdings' Corporate Strategy Division. ”Roll-to-roll production will help lower [our] costs,” he adds, referring to a method of producing electronic devices on rolls of material such as plastic, which could be produced in long sheets.
To date KM has produced its OLED lighting using a vacuum evaporation process. ”This has to change to a solution or film process suitable for roll-to-roll manufacturing,” KM's Komamura emphasizes.
The Yamagata University group has also been experimenting with both vacuum evaporation and roll-to-roll processes. But Kido believes the latter method—at least when the OLED solution is applied via inkjet printing—is a long way from commercial viability. ”With vacuum evaporation you can create a four- or five-layer structure very easily,” says Kido.
KM has a different view, pointing to a century of experience in producing photographic film—a business it exited last year in order to focus on new technologies such as OLED development. The company remains coy about its approach to roll-to-roll production. But KM hints that rather than using inkjet printing to apply the OLED material, it is tapping its film-making know-how to pursue a ”coating process” that will enable it to lay down ”multilayers” of the solution during the roll-to-roll process.
With either process, what's clear is that after two decades of research, OLEDs are just about ready to light up the industry.