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.