Highly efficient inverted top-emitting organic electroluminescent devices with doped charge transport layers

We report on monochrome top emitting organic light emitting diodes (OLEDs) with inverted layer structure and discuss the optical and electrical optimization of OLED devices comprising the orange phosphorescent emitter Ir(MDQ)₂(acac). We show that first, charge balance within the emitting layer is an important factor for efficient generation of light and second, optical outcoupling is a critical issue in top-emitting devices. We demonstrate the use of doped charge transport layers for efficient injection of charge carriers and optical modeling to improve outcoupling. The latter one is done via optimized cavity tuning and application of a dielectric capping layer. Finally, driving voltages of 4.2V at 1000 cd/m², 19 lm/W and 17% external quantum efficiency (EQE) from devices made on metal substrates are reached.