Highly efficient inverted top emitting organic light emitting diodes using a transparent top electrode with color stability on viewing angle

We report a highly efficient phosphorescent green inverted top emitting organic light emitting diode with excellent color stability by using the 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile/indium zinc oxide top electrode and bis(2-phenylpyridine) iridium(III) acetylacetonate as the emitter in an exciplex forming co-host system. The device shows a high external quantum efficiency of 23.4% at 1000 cd/m(2) corresponding to a current efficiency of 110 cd/A, low efficiency roll-off with 21% at 10 000 cd/m(2) and low turn on voltage of 2.4 V. Especially, the device showed very small color change with the variation of Delta x = 0.02, Delta y = 0.02 in the CIE 1931 coordinates as the viewing angle changes from 0 degrees to 60 degrees. The performance of the device is superior to that of the metal/metal cavity structured device. (C) 2014 AIP Publishing LLC.