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^-1 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^-1, with EQE and PE values of 17.0% and 25.1 lm W^-1at a luminance of 1000 cd m^-2, 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).