Exploiting Ultrathin Layer to Realize Simultaneous High Electroluminescence Efficiency and Color Quality in Hybrid White Organic Light-Emitting Diodes.

Highly efficient white organic light-emitting diodes (WOLEDs) created by combining phosphorescent and thermally activated delayed fluorescence (TADF) emitters have advanced rapidly as cutting-edge technology for their potential applications in flat-panel displays and solid-state lighting. However, achieving high device performance while simultaneously ensuring a high white color quality remains a challenge. Here, we demonstrate efficient WOLEDs, fabricated by using a blue TADF emitter with an orange phosphor in a single emissive layer, enabling the generation of white light. The WOLEDs exhibit outstanding electroluminescent (EL) performance, achieving a maximum external quantum efficiency (EQE) of 31.8% and power efficiency (PE) of 56.8 lm W and producing cold and warm white light by varying the concentration of the phosphor emitter. To further enhance the quality of white light without compromising the EL performance, a multilayer sandwich configuration was adopted by introducing an ultrathin (∼1 nm) layer of the efficient green TADF emitter BPyDTC between two white emissive layers. This design strategy resulted in a high-performance WOLED with a maximum EQE of 28.8% and a PE of 65.5 lm W, with EQE and PE values of 17.0% and 25.1 lm Wat a luminance of 1000 cd m, respectively. The emission from all the layers effectively blends, achieving better coverage of the visible spectrum and generating white light with Commission Internationale de l'Eclairage, CIE coordinates of (0.38, 0.41).