Power efficiency improvement in a tandem organic light-emitting diode

When a tandem light-emitting diode (OLED) utilizes unoptimized electroluminescent (EL) units, it is fairly easy to improve the power efficiency of such a device. However, when a tandem OLED utilizes optimized EL units, improved power efficiency can only be achieved if each intermediate connector has excellent carrier injection capabilities along with a negligible voltage drop across it. Four organic intermediate connectors were studied in this work, one of which consisting of a Li-doped 4,7-diphenyl-1,10-phenanthroline layer and a 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile layer, exhibits the best power efficiency improvement for tandem OLEDs. (C) 2008 American Institute of Physics.