Tandem Blue OLEDs Display High Efficiencies
Researchers from Eastman Kodak Co. in Rochester, N.Y., have reported luminous efficiencies of 20 and 38 cd/A with external quantum efficiencies of greater than 11 percent from tandem organic LEDs (OLEDs) emitting in the blue region of the spectrum. They presented their findings at the Society for Information Display’s 44th annual International Symposium, Seminar and Exhibition in San Francisco.
The tandem emitters incorporated the company’s OLED materials and featured electroluminescent units separated by an organic intermediate connector. One device displayed CIE color coordinates of (0.14, 0.17) and a luminous efficiency of 20 cd/A at an applied current density of 20 mA/cm2, and the other displayed coordinates of (0.15, 0.42) and a luminous efficiency of 38 cd/A at 20 mA/cm2. The estimated lifetimes of the OLEDs at an initial brightness of 1000 cd/m2 are more than 10,000 hours and more than 50,000 hours, respectively. The drive voltages of the devices are less than 8 and 6.5 V, respectively, at 1000 cd/m2.
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