Degradation Mechanisms in Blue Organic Light-Emitting Diodes

An organic light-emitting diode (OLED) is required to exhibit long-time operation without degradation as an inorganic LED. Sufficiently long operation time has been demonstrated for green- and red-emitting OLEDs. However, a blue device that is important for full-color display and lighting exhibits a much shorter operational lifetime than the other color devices. The short lifetime is mainly attributed to the molecular dissociation and the defects and radical species formation through various unimolecular and bimolecular processes, including direct photolysis, exciton-exciton interaction, and exciton-polaron interaction, and so on. Different novel techniques of chemistry and physics have been employed for blue devices to suppress the degradation process induced by high-energy excitons. A deep understanding of the degradation mechanism is still needed for all three kinds of blue OLEDs employing fluorescence, phosphorescence, and thermally active delayed fluorescence. In this brief review, we introduce and discuss several degradation mechanisms for these three kinds of OLEDs.