Lanthanide complexes with d-f transition:new emitters for single-emitting-layer white organic light-emitting diodes

摘要

White organic light-emitting diodes(WOLEDs)is a new generation of lighting technology and has stimulated wide-ranging studies.Despite the advantage of simple device structure,single-emitting-layer WOLEDs(SEL-WOLEDs)still face the challenges of difficult material screening and fine energy level regulation.Herein,we report efficient SEL-WOLEDs with a sky-blue emitting cerium(Ⅲ)complex Ce-TBO2Et and an orange-red emitting europium(Ⅱ)complex Eu(Tp2Et)2 as the emitters,showing a maximum external quantum efficiency of 15.9%and Commission Internationale de l'Eclairage coordinates of(0.33,0.39)at various luminances.Most importantly,the electroluminescence mechanism of direct hole capture and hindered energy transfer between the two emitters facilitate a manageable weight doping concentration of 5%for Eu(Tp2Et)2,avoiding the low concentration(<1%)of the low-energy emitter in typical SEL-WOLEDs.Our results indicate that d-f transition emitters may circumvent fine energy level regulation and provide development potential for SEL-WOLEDs.