An efficient dual-emissive-layer white organic light emitting-diode: Insight into device working mechanism and origin of color-shift

By using a single host for both blue and orange phosphorescent dopants, a simple and efficient white organic light emitting-diode is reported. The dual-emissive-layer white device achieves a peak external quantum efficiency of 16.9 +/- 0.9% and power efficiency of 44.1 +/- 2.3 lm/W without out-coupling enhancement. Analysis of the device working mechanism determines that the blue dopant molecules can form a bridge to facilitate electron transport into the adjacent orange emitting-layer. The orange emission originates from both the direct electron trapping by the orange dopant and incomplete blue-orange energy transfer mechanisms. The origin of the voltage-dependent color shift of the device is quantitatively determined according to the working mechanism. Possible solution to reducing the color-shift is also provided based on the calculation and analytical results. (C) 2015 Elsevier B.V. All rights reserved