New study says OLED efficiency is less than previously reported

Aug. 21, 2008
The study's findings -- published online Sunday -- hint that OLEDs would convert no more than 25% of electricity into light, contrary to earlier estimates of up to 63%.
Lupton, Boehme excite organic polymer (Courtesy: Nick Borys) A new study from University of Utah scientists suggests it may be more difficult than thought to make highly efficient LEDs using organic materials. The findings hint such LEDs would convert no more than 25% of electricity into light rather than heat, contrary to earlier estimates of up to 63%.

These scientists came to this conclusion after successfully controlling an electrical current using the "spin" within electrons -- a step toward building an organic "spin transistor": a plastic semiconductor switch for future ultrafast computers and electronics.

The study -- published online Sunday, Aug. 17, in the journal Nature Materials -- was led by Christoph Boehme and John Lupton, assistant and associate professors of physics, respectively, at the U. of Utah, reports Laser Focus World.

"This is the first time anyone has done really fundamental, hands-on quantum mechanics with an organic LED," Lupton says. "This is tough stuff."

Organic semiconductor or "plastic" LEDs are important because they are much cheaper and easier to fabricate than existing inorganic LEDs (which can be made of compounds of gallium, arsenic, indium, and other inorganic materials). Some inorganic LEDs can convert 47% to 64% of incoming electricity into white light rather than waste heat, but are hindered by high costs.

The efficiency of organic LEDs long was thought to have an upper limit of 25%, but then in a 2001 Nature paper by other U. of Utah physicists, it was suggested it might be possible to make organic LEDs that converted 41% to 63% of incoming electricity into light.

However, the new study suggests the 25% efficiency limit may be correct -- at least for the organic polymer studied -- pure MEH-PPV -- and possibly for others.

"Doping" organic semiconductors with other chemicals someday might lead to organic LED efficiencies above 25%, but Boehme says he is skeptical.

However, he adds, even if organic LEDs are less efficient and have a shorter lifespan than inorganic LEDs, they still may be more economical because their cost is so much less.

Boehme says organic LEDs' greatest promise is not in lighting, but to replace liquid crystal display (LCD) technology in modern televisions and computer screens. Organic LEDs will be much cheaper, can be made on flexible materials, have a wider viewing angle and color range, and will be more energy efficient than LCDs, he says.