High-efficiency monochrome organic light emitting diodes employing enhanced microcavities

We demonstrate enhanced light outcoupling from bottom emitting monochrome high- efficiency red, green, and blue organic light emitting diodes by adding silver layers on the indium tin oxide (ITO) anode. The devices contain the phosphorescent emitting dyes tris(2- phenylpyridine )iridium and iridium (III) bis[2- methyldibenzo-(f, h)quinoxaline] acetylacetonate , and the blue singlet emitter 2,2', 7,7'- tetrakis 2,2- (diphenylvinyl) spiro- 9,9'-bifluorene. We follow the p- i- n doping concept to increase the power efficiencies. We reach 81 lm/ W for red, 101 lm/ W for green, and 4.0 lm/ W for blue color. These efficiencies are improved by up to a factor of 2.3 compared to standard ITO devices, which we attribute to microcavity amplification between the cathode and the Ag layer. (c) 2008 American Institute of Physics.