Flat panel displays and lighting based on organic light-emitting diodes (OLEDs) show high efficiencies, are ultrathin, lightweight, and flexible, and can exhibit desirable saturated color coordinates including true black. A decade ago, thermally activated delayed fluorescence (TADF) was reintroduced to the organic semiconductor community by Adachi and co-workers, who demonstrated its great potential in harvesting non-emissive triplet excitons and produced OLEDs with comparable efficiencies to commercialized versions using organometallic phosphorescent emitters. Indeed, TADF OLEDs can achieve up to 100% internal quantum efficiency (IQE) as the emitter is capable of harnessing all the singlet and triplet excitons and converting these to light via emission from the singlet excited state.