White organic light-emitting devices employing phosphorescent iridium complex as RGB dopants

Abstract

Efficient phosphorescent white organic light-emitting diodes (WOLEDs) were realized by using a bright blue-emitting layer, iridium (III) bis-[(4,6- di-fluoropheny)-pyridinato-N, C2′] picolinate doped 4.4′-bis-(9-carbazolyl)-2, 2′-dimethyl–biphenyl doped, together with tris-(2-phenylpyridine) iridium and bis-(1-phenyl–isoquinoline) acetylacetonate iridium (III) are codoped into a 4,4′-N,N′-dicarbazole- biphenyl layer to provide blue, green and red emission for colour mixing. The device emission colour is controlled by varying dopant concentrations and the thicknesses of blue and green–red layers as well as tuning the thickness of an exciton-blocking layer. The maximum luminance and power efficiency of the WOLED are 42700 cd m−2 at 17 V and 8.48 lm W−1 at 5 V, respectively. The Commission Internationale de 1'Eclairage (CIE) chromaticity coordinate changes from (0.41, 0.42) to (0.37, 0.39) when the luminance ranges from 1000 cd m−2 to 30000 cd m−2.