White organic light-emitting diode based on phosphorescence

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Since 1987 Tang and VanSlyke successfully studied a two-layer heterostructure device configuration, organic light-emitting diode (OLED) has attracted much attention. The flat-panel display OLED of new generation was discovered. Orange light-emitting device has many innate advantages than small size LCD, such as self emitting, low consumed power, wide view angle, high brightness, low cost, high contrast, fast response, high brightness, wide view angle, and supports in full color application, etc. Because of these advantages, organic light-emitting device is to be a product that owns the market potential in next generation. Among many colors of light source, white light is the most important of them because it can not only replace the modern fluorescent tube but also be backlight for liquid crystal displays and apply to full color technology. Hence, white organic light-emitting diode plays an important role in optoelectronics technology and the field of display. Generally, the structure of white organic light-emitting device can be divided into two kinds. One is the structure of single layer, and the other is the structure of multilayer. Manufacturing the white organic light-emitting device of single layer is easy, the efficiency of this device don’t still be improved. Therefore, the purpose of this experiment is to fabricate a white organic light-emitting device with high efficiency and high luminescence, so as to improve the efficient problem of white organic light-emitting device with single layer. In this experiment, the structure of white organic light-emitting device was ITO/ NPB/ DPVBi/ CDBP: Ir(btp)2acac/ Alq3/ BCP/ CsF/ Al. All of the organic materials were deposited at ITO substrate. NPB was used as hole-transporting layer, DPVBi was used as blue emitting layer, Ir(btp)2acac was the red fluorescence dye and doped in CDBP. CDBP doped with Ir(btp)2acac that was used as red emitting layer, BCP was used as hole-blocking layer, Alq3 was used as green emitting layer and electron-transporting layer and Al was used as cathode. Here, CsF was used as buffer layer to help electrons inject. The purpose in this experiment is finding the optimum doped rate for CDBP and Ir(btp)2acac in coevaporation and the optimum thickness of three emitting layers. At the same time, we will analyze the optoelectronic characteristics of multilayer white organic light-emitting device. The deposition rate of Ir(btp)2acac in coevaporation would affect the efficiency of energy transfer and thickness of three emitting layers would affect the location of recombination. Therefore, by controlling the deposition rate and thickness of three emitting layers could obtain the multilayer white organic light-emitting device in this experiment. From the experimental results, we could obtain the contribution of red light by complete energy transfer from CDBP to Ir(btp)2acac when the deposition rate in coevaporation was 1: 2.5. At the same time, the optimum thickness of DPVBi and Alq3 was 200Å and 250Å, respectively. Finally, we could obtain the optimum white organic light-emitting device and utilize the characteristic curves of I-V、L-V、EL and PL analyzing the optoelectronic characteristics of white organic light-emitting device. In this study of white organic light-emitting device, we could obtain the optimum structure was ITO/ NPB (200Å)/ DPVBi (200Å)/ CDBP:2.5% Ir(btp)2acac (100Å)/ Alq3 (250Å)/ BCP (50Å)/ CsF/ Al. At this optimum structure, we obtained the best white CIE coordinate was on (0.35, 0.33). When the voltage was at 15 V, the highest luminance of white organic light-emitting device was 7005 cd/m2.