Reduced efficiency roll-off in highly efficient and color-stable hybrid WOLEDs: The influence of triplet transfer and charge-transport behavior on enhancing device performance

By wisely utilizing combinations of exciton-managed orange-phosphorescence/sky blue fluorescence, we report on high-efficiency white organic light-emitting diodes (WOLEDs) with high color-stability together with reduced efficiency roll-off. Two WOLEDs with the peak current efficiencies of 34.5 and 42.5 cd A (1) which slightly shift to 34.2 and 40.0 cd A (1) at 1000 cd m (2) are demonstrated. Systematic investigations focused on the effects of hole-injection buffer layer, thickness of emitting-layer (EML) and the stepwise-doping profile of orange phosphorescent EML on the device performance have been performed. It is evidently shown that careful management of the triplet/singlet excitons and charge-carriers is key to realizing such high performance of the devices. The results will beyond doubt be helpful to the design of both material and device structure for high-performance WOLEDs and next-generation solid-state lighting sources. (C) 2009 Elsevier B.V. All rights reserved.