| Ever since1987C.W Tang invented multilayer organic light emitting diode (OLED) devices, it has attracted the attention of researcher as the the next generation of lighting and display technology. At present, the red and green phosphorescent devices can satisfy the industrialization requirements, but blue phosphorescent devices are still the bottleneck for high efficiency roll off and short device lifetime. Therefore, it is necessary to optimize the device structure to improve the device performance. In this thesis, we designed the simple device structure to reduce the charge accumulation at different interfaces, and improved the composite ratio of the carriers to achieve high device performances. The related points of the work were summarized as followed:In the first chapter, we introduce the basic knowledge and the research progress of organic electroluminescent technology in recent years. And then the design idea and teoretical basis were expounded.In the second chapter, by introducing chloride ions onto ITO surface with physical methods, the work function of the ITO was greatly improved, and the interface barrier of the hole injection/ITO was reduced, which will facilitate the injection and transport of hole carriers. The ITO anode with carbon tetrachloride solution treatment shows significantly higher work function than that of as-cleaned ITO, leading to more efficient hole injection from ITO to organic layers. At the current density of20mA/cm2, the device of ITO with carbon tetrachloride solution treatment showed an improvement of39.35%in current efficiency and66.95%in power efficiency over the as-cleaned device.In chapter three, we fabricated the unilateral homogenous devices with hole transport-type host material TCTA and mCP. The ptimized device with TCTA as host and hole transport material exhibited a high power efficiency of40Im/W and a high external quantum efficiency (EQE) of19.2%. Compared to tranditional OLEDs with NPB as hole transport layer, the efficiencies of unilaternal homogenous OLED increased by32.4%and in64.6%. The device with mCP as the host and hole transport material obtained a maximum power efficiency and external quantum efficiency of36.2lm/W and19%, respectively. And compared with tranditional device, the unilateral homogenous devices’s power efficiency has been improved100%at different brightness.The fourth chapter we used MDBIP and MDBIPy as host to construct unilateral homogeneous devices. The devcie with MDBIP as host and electron transport materail exhibited high efficiencies with maximum current efficiency, external quantum efficiency and power efficiency of63.34cd/A,17.79%and64.66lm/W, respectively. The power efficiency was improved137.46%compared with multilayer heterojunction devices. When MDBIPy was used as host and electron transport material, the device showed a maximum efficiency of74.21cd/A and71.82lm/W, respectively. The efficiencies of unilateral homojunction device are higher than the multi-layer heteroj unction device, showing the imporvement of71.74%and220.2%.The fifth chapter the homogenous device with bipolar transport host was fabricated. Compared with the corresponding multilayer devices, the homogenous device exhibited high efficiencies and low efficiency roll-off due to the broader exciton formation zone and balance of carrier injection and transport. The optimizd device with biplar host of MBICP was fabricated showing a maximum current efficiency, power efficiency and external quantum efficiency of35.2cd/A,33.51m/W and17.7%, respectively Compared with the traditional multilayer heteroj unction device (21.3cd/A,16.8lm/W and10.1%), the improvement of efficiencies are65.6%,99.6%and75.2%, respectively. In addition, we fabricated a double emitting layer (DEML) device with FIrpic doped in a hole-transportmaterial TCTA and an electron-transporting material SPPO13, respectively. The optimized device has a high current efficiency of30.59cd/A, a high external quantum efficiency of15.56%, a high power efficiency of36.571m/W. Compared to OLEDs with only single TCTA-and SPPO13-DEML, the device efficiency of with DMEL increased nearly5-fold.In chapter six we design a new type device with quantum well structrue by using the different materials with different highest molecular orbital (HOMO) and lowest molecular unoccupied orbital (LUMO) energy level to limit the carriers into the light-emitting layer. The optimized device structure exhibited the maximum current efficiency, power efficiency, and external quantum efficiency of40.31cd/A, and20.31%,30.141m/W, respectively. More importantly, the quantum well device structures exhibit very low efficiency roll-off, the external quantum efficiency is still as high as18.86%at brightness of5000cd/m2and maintain more than92.86%of the maximum external quantum efficiency. The good performance of the device with quantum well device structure demonstrated that it is a new rational way to realize the industrialization of the organic electroluminescence light emitting device. |
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