2, University of Michigan, Ann Arbor, Michigan, United States
3, University of Michigan, Ann Arbor, Michigan, United States
High efficiency solid state lighting devices have the potential to significantly reduce lighting energy usage while also offering good color rendering and longer lifetimes than conventional lighting sources. While organic light emitting diodes are promising candidates for this application, their operational lifetime is limited by the blue phosphorescent chromophore. We demonstrate stacked white phosphorescent light emitting devices (SWOLEDs) with lifetimes (as determined from the time it takes to lose 30% of the initial luminance of 1000 cd/m2) of up to 80,000 hours. The correlated color temperature of the devices ranges between 2780-3300 K with color rendering index as high as 89. The three emitter devices (red, green, and blue) contain up to five stacked elements, and employ red emitting blocking layers, stable charge generation layers, graded doping, and hot excited state management to achieve long lifetime. The materials and layer structures used and design principles for SWOLEDs are discussed.