Researchers Boost Brightness Of Energy-Efficient OLED Lighting

A team of University of Florida scientists has found a way to improve the brightness of organic light-emitting diodes, an energy-efficient technology used in mobile phones, cameras, and recently in flat-panel TVs.

UF researchers have set a record in efficiency for blue OLEDs, the color essential to white light. While the scientists have yet to reach their efficiency goal, the advancement takes them much closer in producing high-quality light similar to standard incandescent bulbs, the university said.

OLEDs use a film of organic compounds that produce light when electricity passes through them. The technology can be used in a wide variety of applications, including television screens, computer displays, advertising signage, and portable system screens, such as mobile phones and personal digital assistants.

A significant advantage of an OLED is that it requires less power than alternative technologies. In the case of room lighting, boosting the brightness of white light from an OLED would make the technology an alternative to compact fluorescent bulbs, which use less power than standard incandescent bulbs, but cast a cold light that many people dislike.

"The quality of the light is really the advantage," UF associate professor Frank So said of OLED lighting.

So and his team of UF scientists have built a blue OLED with a peak efficiency of 50 lumens per watt. A lumen is a measure of brightness perceived by human eyes. The achievement is a significant step toward the team's goal of producing white light with efficiency higher than 100 lumens per watt, according to UF.

If the researchers achieve their goal, then they will have produced a form of lighting that So says is highly "tunable." Because each OLED is an individual light, differently colored OLEDs can be combined to produce different shades, which means warm, rich lighting can be easily created.

"The quality of the light generated can easily be tuned by using different color emitters," So said.

The U.S. Department of Energy is funding the research, which has appeared in the journal Applied Physics Letters. Collaborating with So are UF materials science engineering professor Paul Holloway and UF assistant professor Jiangeng Xue.

OLED technology is finding its way in computer screens and digital televisions as an alternative to LCDs and plasma displays. Because OLEDs don't require a backlight like the other technologies, the displays use less power and are thinner.

OLED displays also show more vivid images through better color saturation. This is accomplished through a pixel architecture that stacks red, green and blue subpixels on top of one another in order to create full-color quality.

Despite the advantages, few OLED computer and TV screens are available, because the materials used degrade at a faster rate than technology found in LCDs and plasma displays, which means a far shorter lifespan.

Sony, for example, started offering this year an OLED TV called the XEL-1. However, research firm DisplaySearch found that the screen would lose half its brightness after 17,000 hours of use, which was almost half the time of Sony's estimate. The 11-inch TV costs more than $2,000, which is much more expensive than much larger LCD TVs.