Nearly 100% internal phosphorescence efficiency in an organic light-emitting device

We demonstrate very high efficiency electrophosphorescence in organic light -emitting devices employing a phosphorescent molecule doped into a wide ene rgy gap host. Using bis(2-phenylpyridine)iridium(III) acetylacetonate [(ppy )(2)Ir(acac)] doped into 3-phenyl-4(1'-naphthyl)-5-phenyl-1,2,4-triazole, a maximum external quantum efficiency of (19.0 +/-1.0)% and luminous power e fficiency of (60 +/-5) lm/W are achieved. The calculated internal quantum e fficiency of (87 +/-7)% is supported by the observed absence of thermally a ctivated nonradiative loss in the photoluminescent efficiency of (ppy)(2)Ir (acac). Thus, very high external quantum efficiencies are due to the nearly 100% internal phosphorescence efficiency of (ppy)(2)Ir(acac) coupled with balanced hole and electron injection, and triplet exciton confinement withi n the light-emitting layer. (C) 2001 American Institute of Physics.