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 energy gap host. Using bis(2-phenylpyridine)iridium(III) acetylacetonate $[{\mathrm{(ppy)}}_{\mathrm{2}}\mathrm{Ir(acac)]}$ 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 efficiency of (60±5) lm/W are achieved. The calculated internal quantum efficiency of (87±7)% is supported by the observed absence of thermally activated nonradiative loss in the photoluminescent efficiency of $({\mathrm{ppy)}}_{\mathrm{2}}\mathrm{Ir(acac)}.$ Thus, very high external quantum efficiencies are due to the nearly 100% internal phosphorescence efficiency of $({\mathrm{ppy)}}_{\mathrm{2}}\mathrm{Ir(acac)}$ coupled with balanced hole and electron injection, and triplet exciton confinement within the light-emitting layer.