The Study Of White Organic Light-emitting Diodes Based On The Phosphorescent Dye

Organic light emitting diodes attract a great deal of attention due to their low-voltage operation, wide-viewing angle, high contrast, and mechanical flexibility. In particular, white organic light emitting diodes (WOLEDs) have recently become a global hot pursuit because of their broad prospect of application and large potential market in solid-state lighting and back lighting of flat-panel displays. After nearly20years of development, the organic electroluminescent devices performance and theoretical research have achieved great progress. There have been various approaches to achieve white OLEDs. In this study, based on the present situation of the WOLED, WOLEDs were realized by the different approaches, in order to study the improvement of electroluminescent performances of WOLEDs. The study mainly includes three parts as follows:Firstly, white organic light-emitting diodes (WOLEDs) with high color stability and efficiency were demonstrated by using complementary color emitting scheme. By sandwiching a yellow emitter between two blue emitters and separated by thin spacer layers of CBP, maximum EL exaction and constant contribution ratio of primary color emission were achieved. With this scheme, the device showed about30%enhanced efficiency compared to that of a dual-emitter-layer reference OLED, while there was only a slight change of CIE(x,y) coordinate from (0.34,0.37) to (0.33,0.37) as the luminance increased from1000cd/m2to20000cd/m2. It is believed that the new design in emissive layer of WOLED can fine tune the contribution of primary emission even the combination zone shifted with applied bias changed, resulting in high quality phosphorescent WOLED. Secondly, based on the red, green phosphorescent dyes and a blue fluorescent material, a phosphorescent/fluorescent hybrid white OLED was demonstrated, with the capability of controlling energy transfer. In the WOLEDs, excitons recombination zone was confined in the fluorescent emission layer by managing host structures. And by adjusting the thickness of spacer layers between phosphorescence and fluorescence emission layers, energy transfer can be controlled effectively to realize the white balance and high efficiency of WOLEDs, due to difference of singlet and triplet state excitons. Finally, a high efficiency of29cd/A was achieved. The CIE coordinate of WOLEDs is (0.33,0.32) at luminance of1000cd/m2.Finally, based on a new polymer of PF-DTFO, the novel white-light polymer light-emitting diode (WPLED) was introduced with the structure of ITO/PEDOT:PSS/PF-DTFO/LiF/Al. Because of its excess blue emission, modified WPLEDs were developed by doping phosphorescence dye of FIrpic in emission layer. In the WPLEDs, triplet excitons’energy can transfer from FIrpic to long-wave emissive groups of PF-DTFO, therefore long-wave emission intensity of PF-DTFO was increased. By using this phosphorescence sensitizer layer, both singlet and triplet excitons can be effectively employed, and the performance of the PWOLED was improved. The PWOLED shows a little change of CIE coordinate from (0.33,0.38) to (0.32,0.38) as the driving voltage increased from8V to16V, simultaneous, the device shows about38%enhanced efficiency compared to that of unoptimized WPLED.