Samsung Advanced Institute of Technology

The horizontal orientation of the transition dipole moment of the phosphorescent emitters has been understood to be an important factor to enhance external quantum efficiency of organic light-emitting diodes (OLEDs) through improving light out-coupling in optical microcavity structures. Here, we report red-emitting heteroleptic iridium (III) complexes exhibiting an extremely high horizontal ratio of emitting dipole orientation (EDO) and photoluminescence quantum yield (PLQY) as well as longer operational device lifetime without scarifying any other photophysical properties. The systematic molecular design of main and ancillary ligands in heteroleptic iridium complexes led to achievement of both a horizontal EDO of 92% and a PLQY of 98% in the red-emitting phosphorescent devices along with a shorter exciton decay time of 0.71 μs. Accordingly, the red-emitting devices showed excellent performances of maximum external quantum efficiency of 32% and low efficiency roll-off with the 1931 Commission Internationale de L？Eclariage coordinates (CIE) of (0.66, 0.34). Therefore, our approach opens the way for further development of new red-emitting iridium complexes pushing the device efficiency toward the theoretical limits.