White organic LEDs advance

If organic light-emitting diodes that glow white (so-called WOLEDs) can be made sufficiently robust, energy-efficient, and economical to manufacture, they may one day supplant incandescent bulbs and other lighting technologies. The latest advance on this long road is a new WOLED architecture that uses a fluorescent blue-emitting dopant in combination with phosphorescent green and red dopants to convert electricity into white light (Nature 2006, 440, 908). Previous WOLEDs used phosphorescent blue, green, and red dopants, but the blue phosphor required too much power to excite, according to Stephen R. Forrest of the University of Michigan, Ann Arbor. Forrest, until recently at Princeton University, and his colleagues there and at the University of Southern California replaced the blue phosphor with a commercial blue fluorescent compound, 4,4'-bis(9-ethyl-3-carbazovinylene)-1,1'-biphenyl. In this way, they were able to boost the power efficiency by about 20% and achieve a stable white color regardless of the brightness level. The device eventually could become four to five times more efficient than standard incandescent light bulbs, Forrest tells C&EN.