Study On Improving The Stability And Efficency Of Blue Organic Light-emitting Devices

Comparing with other light-emitting devices, organic light-emitting devices have many advantages, such as low drive voltage, high brightness and efficiency, wide visual angle, high contrast ratio, fast response and so on. For this reasons, organic light-emitting devices have shown vast potential applications in flat panel display. And it is believed to be the main stream of the next generation of display devices. Blue organic light-emitting devices as one of the tri-color for realizing full-color display, still have many shortages, such as low brightness and efficiency, bad color purity and stability. It will bring a rapid development for flat panel display, if these problems can be improved or solved. This thesis focuses on how to improve and enhance the stability and efficiency of blue organic light-emitting devices. The main contents include the following components:1. The organic electroluminescent devices will produce a large amount of Joule heat in practical applications. We simulate the actual application. Monitor the spectra of a blue organic material SPBF under different temperature to investigat its stability in the device application. By studying the absorption spectra, excitation spectra changes with temperature, analyse the reason for the long-wave emission appeared as the temperature increased and disappeared as the temperature decreased.2. By optimizing the device structure, for example, inserting a hole blocking layer between the light-emitting layer and the electron transporting layer, modifying the positive and negative electrodes, the electroluminescent properties of blue organic light-emitting devices using SPBF as the emitting layer are improved. It is evident that the performance of blue organic light-emitting device has been improved effectively after optimizing the structure of device.3. The effect of different hole injection layers on the performance of blue organic light-emitting devices are studied, using PEDOT:PSS, evaporated CuPc and water-soluble CuPc as hole injection layer, respectively. The results show that the performances of device with water-soluble CuPc as hole injection layer are better than that of the device with PEDOT:PSS, but worse than that of the device with deposited CuPc. In addition, the effects of film thickness and the fabricating methods of water-soluble CuPc on the performances of blue organic light-emitting devices are studied. We use two heat treatment ways on the films, as one is spin-coating the film on heated substrate and then annealing, the other is spin-coating the film on room temperature substrate and then annealing. The results show that the surface roughness of the film fabricated during heating is significantly smaller and the device performance is the best.4. The photoluminescence and electroluminescent characteristics and luminescence mechanism of the blue phosphorescent material Ir(Fppy)3doped system with different doping concentration are studied. The experimental results show that the mechanisms of photoluminescence and electroluminescent are different. There exists energy transfer between host and guest materials in photoluminescence, and it is enhanced as the doping concentration increasing. In the process of electroluminescence, the emitting of the guest material mainly comes from the carrier capture of the guest material. When the doping concentration is increased, more carriers are captured by the guest material, and the luminous performances of the devices are enhanced. In addition, the effects of single-wall carbon nanotube (SWCNT) on the performance of blue phosphorescence organic light-emitting diodes are investigated by altering the place of SWCNT in prepared devices. The results show that incorporation SWCNT and PEDOT:PSS can generate defects and retard the holes transport ability in PEDOT:PSS. Doping SWCNT into light-emitting layer can improve the transport characteristics of polymer significantly, which leads to excess holes injection and a lower luminous efficiency. Inserting SWCNT between the light-emitting layer and the electron injection layer can enhance electron injection and the luminous efficiency.