Doping-free tandem white organic light-emitting diodes

Tandem white organic light-emitting diodes（WOLEDs） are of great research interest since they can greatly boost the performance compared with the single-unit counterparts. However, their structures are more complicated than those of single-unit OLEDs. Besides, to achieve high performance, the doping technology is required to tandem OLEDs, particularly for tandem WOLEDs, further complicating the structures. Herein, doping-free tandem WOLEDs, for the first time, have been demonstrated. By managing an effective doping-free charge generation layer to interconnect doping-free emitting layers/charge transport layers, high-performance doping-free tandem WOLEDs have been developed. The blueyellow device accomplishes the simplified structure/short fabrication time/reduced cost/high efficiency/low efficiency roll-off/low voltage/high luminance trade-off, which cannot be achieved by previous tandem WOLEDs. Remarkably, the efficiency(81.2 cd A-1) is 2-fold higher than the highest efficiency of previous doping-free WOLEDs and even higher than those of some best doping tandem WOLEDs. The maximum luminance is 44,886 cd m-2, which is the highest for doping-free WOLEDs.Besides, the blue-red device can exhibit a color rendering index（CRI） of 67, which is even higher than that of some representative three-color tandem WOLEDs. Such findings may not only represent a significant step for doping-free WOLEDs, but unlock a novel avenue that doping-free tandem WOLEDs are promising to achieve the simplicity and high performance trade-off.