White Organic Light Emitting Diodes Via Complementary Color Mixing Approach Through Multilayer Device Architecture
White organic light emitting diodes (WOLEDs) are emerging as potential light emitting technology and have found many applications from back light for liquid crystal displays to next generation displays and solid-state lighting. We report here the fabrication of organic light emitting diodes (OLEDs), which emit white light via multilayer color approach. These WOLEDs incorporated the materials emitting two complementary colors greenish-blue and reddish-orange to make white. The amount of light emitted from each layer was chosen in such a way that the mixture of the two emitted lights gave white light. The amount of light emitted from each layer was controlled by taking optimum thickness of each layer and incorporating a thin hole blocking layer of BCP in between the emissive layers. For greenish-blue light, we used a phosphorescent dopant FIrPic whereas for reddish-orange light we used the phosphorescent dopant Ir(btp)2(acac) and both of these dopants were doped in the host CBP. We studied the effect of operating voltage on the color of the emitted light of these WOLEDs and found that the color of the emitted light was almost independent of operating voltage. The WOLEDs emitted 1600 cd/m2 at 15 V with Commission Internationale de I’Eclairage (CIE) coordinates (0.25, 0.32). We also studied the current density vs voltage (J-V) and voltage vs luminescence (V-L) characteristics of these devices and calculated their efficiency which was found to be 0.35 cd/A. We also prepared some WOLEDs based numeric displays just of the demonstration purpose.
Organic light emitting diodes, WOLEDs, Electroluminescence, Exciton recombination, Charge transport layers, Thin films, Thermal evaporation
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