Highly Efficient Organic Light-Emitting Diodes with Phosphorescent Emitters Having High Quantum Yield and Horizontal Orientation of Transition Dipole Moments

Ancillary ligands in heteroleptic iridium complexes significantly influence the orientation of the transition dipole moments. Ir(ppy)(3), a homoleptic iridium complex, exhibits isotropic dipole orientation, whereas the heteroleptic Ir complexes of Ir(ppy)(2)tmd show a highly preferred dipole orientation (78%) in the horizontal direction. In addition, we demonstrate an unprecedented highly efficient green OLED exhibiting an EQE of 32.3% and a power efficiency of 142.5 lm/W by using an emitter with high quantum yield and horizontally oriented dipoles.