Reduced Efficiency Roll-Off in White Phosphorescent Organic Light-Emitting Diodes Based on Double Emission Layers

We demonstrate high-efficiency white phosphorescent organic light-emitting diodes with low efficiency roll-off. The feature of the device concept is employing two phosphorescent emission layers (EMLs) separated by a mixed interlayer. Both the EMLs are doped by two phosphorescent dyes. The resulting white device with the optimized doping concentration shows a maximum efficiency of 31.0 cd/A with extremely low efficiency roll-off of 30.7 cd/A at 1000 cd/m(2), 27.2 cd/A at 5000 cd/m(2), and 25.5 cd/A at 10,000 cd/m(2), respectively, without any outcoupling structures. This is enabled by the balanced charge carrier transport in EMLs, leading to broader exciton recombination zone.