White OLEDs are already producing more light per watt than incandescent bulbs, according to engineering professor Stephen Forrest from Michigen University, but it is trapped inside the device. By fabricating a tandem system of grids and micro lenses on a white OLED, the device can achieve a brightness of over 70 lumens per watt, compared with 15 lumens for incandescent bulbs--almost as much as fluorescent tube lights (90 lumens).
"We have achieved 78 lumens using our grid and lens structures--almost as much as fluorescents," said Forrest. "And when you consider that a lot of the fluorescent tubes light is lost, since it comes out it all directions around the tube, our white OLEDs will be perceived in many applications as brighter than fluorescents."
Unfortunately, up to 60 percent of the light generated by white OLEDs is trapped inside the semiconducting layers--reflected back from the glass lid of the device. Instead, Forrest uses a layer of grids etched in silicon dioxide that refracts the trapped light through the glass lid into a layer of dome-shaped micro-lenses that direct the trapped light out of the device.
Forrest's research has been funded by Universal Display Corporation and the Department of Energy. Forrest plans to work together with UDC to make brighter and cheaper grids and lenses.