In this paper, we report on the fabrication of multilayer organic light emitting diodes (OLEDs) with high electroluminescent (EL) yield achieved by integrating two units of green-emissive devices in series. The architecture of the device used in the experiment is Indium-Tin-Oxid (ITO)/CuPc/NPB/C545T: Alq3/Alq3/Mg:Alq3/WO3/NPB/C545T: Alq3/Alq3/LiF/Al. We found the efficiency of the two-unit devices can be controllable by the thickness of WO3. The two-unit devices with 1-nm-thick WO3 produces the luminance efficiency of 49.2 cd/A at 20mA/cm2, which is around four times that of the controlled single-unit device (ITO/CuPc/NPB/C545T:Alq3/Alq3/LiF/Al). Compared with reported research data, the "amplification effect" discovered in our device is a rather unexpected result. The external quantum efficiency of 12.6%, with near-saturated Commission Internationale d'Eclairage coordinates (CIEx = 0.27, CIEy = 0.68), is one of the best ever reported for a fluorescent dye-doped OLED. We also demonstrate that the electron injection layer of Mg:Alq3 is a necessary component for the enhancement of EL efficiency. These results may prove to be an effective method to enhance the efficiency as well as the lifetime of current OLEDs.
|Number of pages||5|
|Journal||Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers|
|Issue number||9 A|
|State||Published - 1 Sep 2004|
- High efficiency