Highly efficient single-layer dendrimer light-emitting diodes with balanced charge transport

High-efficiency single-layer-solution-processed green light-emitting diodes based on a phosphorescent dendrimer are demonstrated. A peak external quantum efficiency of 10.4% (35 cd/A) was measured for a first generation $\mathrm{fac-}\mathrm{tris}\text{(2-}\mathrm{phenylpyridine})$ iridium cored dendrimer when blended with ${\text{4,4}}^{\prime }-\mathrm{bis}\mathrm{(N-}\mathrm{carbazolyl})\mathrm{biphenyl}$ and electron transporting $\text{1,3,5-}\mathrm{tris}\text{(2-N-}\mathrm{phenylbenzimidazolyl})\mathrm{benzene}$ at 8.1 V. A maximum power efficiency of 12.8 lm/W was measured also at 8.1 V and 550 cd/m². These results indicate that, by simple blending of bipolar and electron-transporting molecules, highly efficient light-emitting diodes can be made employing a very simple device structure.