| 초록 |
The efficiency of conventional bottom-emitting organic light-emitting diodes (OLEDs) has been steadily improved during the last few decades achieving an external quantum efficiency (EQE) of about 30% in green, 30% in blue, 25-26% in red and 25% in white OLEDs in recent years. Under the assumption that the emitting dipoles exhibit isotropic orientation, the theoretical limit of the EQE of OLEDs is approximately 30%. Therefore, the recently reported EQE of OLEDs seems to have reached its ultimate limit. However, it has been recognized in recent years that some phosphorescent dyes can have preferred orientations. The outcoupling efficiency of the emitted light from the horizontally oriented dipoles of emitters can be much higher than isotropic ones. Here we report that an OLED containing a phosphorescent emitter with horizontally oriented dipoles in an exciplex-forming co-host that exhibits an extremely high EQE over the conventional theoretical limit. |
