Manipulation of blue TADF top-emission OLEDs by the first-order optical cavity design:toward a highly pure blue emission and balanced charge transport

The broad luminescence spectrum of a thermally activated delayed fluorescence(TADF)organic light-emitting diode(OLED)is a critical issue to overcome for its application in high-color-purity displays.Herein,a novel device structure that utilizes the first-order microcavity optical mode with a high radiance intensity is demonstrated to solve this problem by considering the charge transport properties through the analysis of hole-only and electron-only devices.In addition,by tuning the optical interference near the semitransparent top cathode layers consisting of thin silver and organic capping layers,light extraction is increased by nearly 2 times compared to the device without a capping layer.Consequently,the optimized blue TADF top-emission OLED exhibits much lower full width at half-maximum,higher maximum current efficiency,and external quantum efficiency compared to the device before optimization.This approach is expected to provide a simple but effective way to further enhance the spectral purity of the conventional TADF-based OLEDs.