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

We describe the performance of an organic light-emitting device employing t he green electrophosphorescent material, fac tris(2-phenylpyridine) iridium [Ir(ppy)(3)] doped into a 4,4(')-N,N-'-dicarbazole-biphenyl host. These de vices exhibit peak external quantum and power efficiencies of 8.0% (28 cd/A ) and 31 lm/W, respectively. At 100 cd/m(2), 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 in ternal efficiency. In addition, the short phosphorescent decay time of Ir(p py)(3) (< 1 mu s) reduces saturation of the phosphor at high drive currents , yielding a peak luminance of 100 000 cd/m(2). (C) 1999 American Institute of Physics. [S0003-6951(99)00127-8].