Very high-efficiency green organic light-emitting devices based on electrophosphorescence

We describe the performance of an organic light-emitting device employing the green electrophosphorescent material, fac tris(2-phenylpyridine) iridium $[Ir(ppy)3]$ doped into a $4,4′-N,N′$-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 $Ir(ppy)3,$ leading to a high internal efficiency. In addition, the short phosphorescent decay time of $Ir(ppy)3$ (<1 μs) reduces saturation of the phosphor at high drive currents, yielding a peak luminance of 100 000 cd/m².