The reduced triplet-triplet annihilation of electrophosphorescent device doped by an iridium complex with active hydrogen

We demonstrate high efficiency electrophosphorescent devices doped by bis(2-phenyl-benzoimidazole) iridium (III) acetylacetonate [Ir(ppi)(2)acac] with active hydrogen. At 100 mA/cm(2) 2 wt % Ir(ppi)(2)acac doped device offers an external quantum efficiency (eta(ext)) of 5.1% and an efficiency roll-off of 28.2%, which decreases for 33.5% and 39.1% compared with that of 2 and 6 wt % fac-tris(2-phenylpyridine) iridium (III) [fac-Ir(ppy)(3)] doped reference devices, respectively. 7 wt % Ir(ppi)(2)acac doped device behaves a maximum eta(ext) of 13.4% and a eta(ext) of 8.0% at a luminance of 10 000 cd/m(2). Both the eta(ext) are higher than that of the reference device. The improvement in electroluminescent performance was assumed to be the very short triplet lifetime (3.74 ns) induced by the active hydrogen atom. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2998571]