High-Efficiency White Organic Light-Emitting Diodes Based on All Nondoped Thermally Activated Delayed Fluorescence Emitters

While phosphorescent white organic light-emitting diodes (WOLEDs) have attracted great attention due to their high efficiencies, the complex device structure (e.g., host-dopant systems) and the adoption of novel metals (e.g., Ir or Pt) inevitably increase the fabrication complication and manufacturing cost. Herein, a simple and cost-effective structure based on all thermally activated delayed fluorescence (TADF) emitters is proposed to achieve high-performance WOLEDs. The key feature of the WOLED structure is to insert an orange-red TADF ultrathin layer within the nondoped blue TADF emitter, which can significantly reduce the energetic loss and therefore the operating voltage during electron-photon conversion process. After optimizing the energy transfer and exciton formation region between two color-complementary TADF emitters, the all-fluorescence WOLEDs exhibit an extremely high external quantum efficiency of 24.2% with a turn-on voltage of 2.5 V and a color rendering index of >80. It is anticipated that the results will pave the way to the realization of high-efficiency and low-cost WOLEDs that can outperform the typical phosphorescent devices.