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.

We describe the performance of an organic light-emitting device employing the green electrophosphorescent material, fac tris(2-phenylpyridine) iridium $[{\mathrm{Ir(ppy)}}_{\mathrm{3}}]$ doped into a ${\text{4,4}}^{\prime }{\mathrm{-N,N}}^{\prime }$ -dicarbazole-biphenyl host. These devices exhibit peak external quantum and power efficiencies of 8.0% (28 cd/A) and 31 lm/W, respectively. At 100 cd/m², the external quantum and power efficiencies are 7.5% (26 cd/A) and 19 lm/W at an operating voltage of 4.3 V. This performance can be explained by efficient transfer of both singlet and triplet excited states in the host to ${\mathrm{Ir(ppy)}}_{\mathrm{3}},$ leading to a high internal efficiency. In addition, the short phosphorescent decay time of ${\mathrm{Ir(ppy)}}_{\mathrm{3}}$ (<1 μs) reduces saturation of the phosphor at high drive currents, yielding a peak luminance of 100 000 cd/m².