| Display technology, another frontier after the advent of microelectronics and computer science, has a large market potential, and its constant progress brings about great convenience to the human society for the highly-efficient and prompt acquisition of information. As a novel branch in the field of display, organic light-emitting diode, i.e. OLED, has been one of the hottest topics among researchers all over the world. After two decades'development, significant achievements of study on OLED have been obtained in both theory and experiment. This thesis is concerned about the investigation of doped polymer OLED (doped-PLED) and its fabrication techniques. In view of the distinguishing advantages of polymers compared to organic small molecular materials and the low cost as well as the simplicity of spin-coating method, PLEDs consisting of diverse doped polymer systems were fabricated. Their optoelectronic performance and the morphology of thin films were measured and analyzed. Theoretical explanations were presented to these experimental results.Firstly, the background and development status of OLED are reviewed. Relevant principles about organic electroluminescence is introduced, which is the theoretical basis for the investigation in this work.Heterojunction double-layer green devices were fabricated by using doping systems comprised of different polymers and small molecules as the composite hole transporting layer and the traditional green emitting material Alq3 as both emitter and electron transporting layer. Systematical investigation was carried out on device performance, where dielectric PS/TPD and PS/NPB doping systems of different doping concentrations acted as composite hole transporting layer, respectively. The solvent impact on spin-coated film quality and device performance was studied with regard to conductive PVK/TPD and PVK/MEH-PPV doping systems. Results demonstrated that the hole transporting capacity of different composite hole transporting layers is discrepant, which has a remarkable impact on device performance. The optimum doping concentration of a certain system is beneficial to the maximum improvement of device performance. Solvent exhibits an important influence on film property, and device performance could be further enhanced by choosing the proper solvent.Investigation on the electroluminescent characteristics of two novel fluorene-based polymers PFC2 and PFC4 was carried out. Devices with different structures were designed according to material property. The hole transporting capacity and emitting performance of these materials were measured. Doping systems consisting of PFC2/PVK and PFC4/PVK were constructed. Results showed that these novel fluorene-based polymers can be used not only as hole transporting materials, but also as superior blue-emitting materials. In their PVK doping systems, devices exhibit consecutive color variation from green to blue region under different bias voltages resulted from the modulation function of electric field on the tunneling effect of carriers. These devices realize the function of color tuning via voltage control. Meanwhile, effective F?rster energy transfer mechanism might exist between the molecules of different materials in doped devices, which remarkably improves the device performance. This study implied that device luminance and efficiency could be enhanced through energy transfer process by physical doping method, which proves to be a simple and effective approach for device optimization and improvement. Furthermore, it is also proved that PFC2 and PFC4 are a kind of promising polymer materials for their application in blue OLED.In summary, from the point of view of material selection and device optimization, this thesis dicussed in detail different aspects of concentration coordination, current conduction, film morphology, energy transfer, technique improvement and so on in doped PLED, which may be a helpful reference and guide for the future work in the field of polymer organic electroluminescence. |
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