Efficient Hybrid White Organic Light-Emitting Diodes with Superior Color Stability and Slow Efficiency Roll-off Based on Ultrathin Emitting Layer Structures

In this work, high-performance hybrid white organic light-emitting diodes (WOLEDs) with high efficiencies, slow roll-off and excellent color stability were realized by strategically inserting ultrathin red phosphorescent emitter film into bluish-green thermally activated delayed fluorescent (TADF) light-emitting layer (EML). Experimental results demonstrated that the introduction of ultrathin phosphor film helps to harvest superfluous triplet excitons within bluish-green EML and relieve local exciton accumulation-induced quenching, thereby guaranteeing high exciton utilization probability. Besides, the strong holes' trapping of ultrathin layer leads to improved carriers balance, thus realizing stable recombination zone. Finally, the optimal hybrid WOLED obtained the maximum current efficiency (eta(c)), power efficiency (eta(p)) and external quantum efficiency (EQE) of 63.84 cd A(-1), 66.06 lm W-1 and 28.16%, respectively. At the brightness of 1000 cd m(-2), eta c, eta p and EQE as high as 57.14 cd A(-1), 49.88 lm W-1 and 25.23%, respectively, can still be remained by the same device, manifesting slow efficiency roll-off. In addition, the resulting WOLED displayed excellent color stability with slightly shifted Commission Inter-nationale de l'Eclairage coordinates (CIEx,y) from (0.43, 0.44) at 1000 cd m(- 2) to (0.41, 0.43) at 10000 cd m(- 2).