We investigate the average orientation of the transition dipole moments of two green phosphorescent emitters and embedded in a CBP matrix, using in-situ angle resolved electroluminescence spectroscopy and optical simulations. The dipole orientation of is nearly isotropic while 77% of the dipoles are horizontally aligned for . Optimized organic light-emitting diodes based on these emitters achieve external quantum efficiencies of 18.3% () and 21.7% (). This difference is partially explained by the different dipole orientations.
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