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8 October 2005 High efficiency and low voltage p-i-n top emitting organic light-emitting devices
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We present highly efficient, low voltage top emitting organic light-emitting diodes (OLEDs) employing the same material (Ag) for both anode and cathode. Benefiting from doped charge carrier injection and transport layers (p-i-n structure) the diodes show comparable or even better electric characteristics than similar bottom emission OLEDs although the work function of the electrodes in the top emission OLEDs and the HOMO/LUMO location of the transport materials do not coincide. A green top emitting OLED with an Ir(ppy)3 doped double emission layer (D-EML) is demonstrated showing an efficiency of 50 cd/A at a brightness of 1000 cd/m2 and at the same time needing a very low driving voltage of only 2.85 V for 1000 cd/m2. By putting an additional organic capping layer on top of the cathode, the optical structure of the device can be tuned and the efficiency of the diodes can be further improved to a maximum efficiency of 78 cd/A at a brightness of 1000 cd/m2. Using the same capping strategy, efficient phosphorescent red and fluorescent blue top emitting OLEDs are demonstrated with efficiencies at 1000 cd/m2 as high as 13.6 cd/A and 8.6 cd/A, respectively.
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Qiang Huang, Karsten Walzer, Martin Pfeiffer, Gufeng He, Karl Leo, Michael Hofmann, Thomas Stübinger, and Martin Vehse "High efficiency and low voltage p-i-n top emitting organic light-emitting devices", Proc. SPIE 5937, Organic Light-Emitting Materials and Devices IX, 593711 (8 October 2005);

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