High-efficiency white organic light emitting devices with three separate phosphorescent emission layers

We demonstrate high-efficiency white organic light emitting devices (WOLEDs) employing three adjacent phosphorescent emission layers (3-EMLs). The metal-organic dopants for red, green, and blue emissions are each doped in separate hosts, allowing for separate optimization of the three dopant-host material combinations. This structure distributes the exciton generation region across the three hosts to form a stepped progression of highest occupied and lowest unoccupied molecular orbitals. The 3-EML WOLED has a color rendering index of 81 and peak forward-viewing external quantum (EQE) and power efficiencies (PE) of (16.6 +/- 0.8)% and 32 +/- 1 lm/W, respectively, corresponding to a total EQE=(28 +/- 1)% and a total PE=54 +/- 3 lm/W. When an n-doped electron transporting layer is used, the total PE peaks at 64 +/- 3 lm/W, and rolls off to 34 +/- 2 lm/W at 1000 cd/m(2). (c) 2007 American Institute of Physics.