Precise Exciton Management of Quaternary Emission Layers for Highly Stable Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence

Simultaneous achievement of both high electroluminescence efficiency and high operational stability in organic light-emitting diodes (OLEDs) is required for their use in various practical applications. Although OLEDs based on thermally activated delayed fluorescence-assisted fluorescence (TAF) are considered to possess a promising device architecture to exploit the full potential of OLEDs, the operational stability of such systems still requires further improvement. In this study, a quaternary emission layer consisting of a combination of TAF and mixed-host systems is developed. OLEDs containing this emission layer show improved operational stability through the management of exciton generation processes while maintaining high electroluminescence efficiency. Furthermore, a gradient of the mixed ratio of the co-host matrix is used to optimize the recombination zone profile in the emission layer, leading to 17 times improvement of the operational lifetime compared with that of the corresponding single-host-based device. This research provides a simple and general method to develop highly stable TAF-OLEDs.