Of the various competing display technologies used in the modern world, that of the organic lightemitting diode (OLED) is rapidly becoming one of the most widely adopted. This is because OLEDs offer numerous advantages over other display technologies, including high efficiencies, the capacity to view the display at wide angle without loss of image quality, improved contrast, faster refresh rate and an access to a multitude of form factors. In particular, OLEDs can be integrated into flexible and foldable displays and lighting panels, something that is not possible with other display technologies. In an OLED, light is generated by the radiative decay of an exciton that forms following electrical excitation of an emitting molecule, which can be, for instance, an organic (or organometallic) smallmolecule or polymer that is located centrally in a stack of organic semiconducting layers sandwiched between two electrodes. The overall efficiency of an OLED is quantified in terms of its external quantum efficiency (EQE), which relates to the ratio of supplied electrons to observed photons.