are thought to limit the performance of phosphorescent OLEDs and TADF OLEDs. [10,11] During OLED operation, the triplet-polaron interaction causes undesirable efficiency roll-off (i.e., increased quenching of excited states at higher current densities) and degradation (e.g., increasing the number of molecules with some of their intramolecular bonds irreversibly dissociated), resulting in less emitted light. Understanding and managing exciton dynamics is therefore of great significance in the design of modern TADF OLEDs. [12,13] These internal nanoscale processes are often difficult to observe, so there is

The emission zone profile in an organic light-emitting diode was extracted by fitting the experimentally measured far-field angular electroluminescence spectrum of a purposely designed device. It is based on a thin 10 nm emission layer doped with the red emitting phosphor Ir(MDQ)2acac. We find strong indications for light emission originating from outside of the emission layer, even though the device has electron and hole blocking layers. These are commonly assumed to completely confine the charge carrier recombination and hence the light emission to the emission layer. Since the calculated internal spectrum of the emission matches the emitter photoluminescence spectrum well, diffusion of the emitter molecules outside of the emission layer is hypothesized

Emitter orientation will play a major role in future applications of organic light-emitting diodes due to its strong impact on the efficiency of the devices. Up to now, determining the orientation of transition dipole moments required elaborate angular-dependent measurements of the light emission pattern. In this paper, we present a simplified and straightforward method to extract the emitter orientation from external quantum efficiency measurements. We demonstrate the validity of the method on three different dye-doped emitting systems