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. [ABSTRACT FROM AUTHOR]