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Research on the Surface Modification of Light Emitting Materials of OLED Quinoline Metal Complexes

Author: ZhangJunPing
Tutor: XuBingShe
School: Taiyuan University of Technology
Course: Materials Processing Engineering
Keywords: OLED SiO2 coated 8-hydroxyquinoline
CLC: TB34
Type: Master's thesis
Year: 2011
Downloads: 67
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Abstract

With reaching a consensus on the development of "low-carbon economy" all over the world, top priority has been given to the development of organic light emitting devices (OLEDs) in the area of light and illuminating industry, which can be mainly attributed to its advantage of environment friendly, low power consumption and high efficiency properties.However, OLEDs’s relatively short lifetime and low power-conversion efficiency have seriously hindered its futher industrialization process in the real world, therefore, a great deal of work still needs to be done to improve or overcome its disadvantages immediately. In this paper, inorganic silica film are coated on the light-emitting materials by the method of improving the physical and chemical properties of the surface of the light-emitting material of OLED with a view to reducing the erosion effect of moisture and oxygen on the matrix materials, which will consequently play a protective effect on the light-emitting materials and extent the lifetime of the devices mentioned above.In the paper sodium silicate and TEOS were chosen as the silica source, respectively, while the organic metal complexes 8-hydroxyquinoline zinc (Znq2) and 8-hydroxyquinoline aluminum (Alq3) as the substrate with their surfaces being coated to improve the relevant properties, the concrete procedures are as follows:1. Silica-coated Alq3 was synthesized through the method of liquid phase deposition with sodium silicate and TEOS as the silica source, respectively, self-made of Alq3 as the substrate as well as under the condition that molar ratio of Si to Alq3 equals 1:10. The scanning electron microscopy, transmission electron microscopy, photoluminescence spectroscopy and thermal gravimetric analysis were then used to demonstrate the morphology, luminescent properties and thermal stability of the products, respectively. In particular, the microscope morphology of the film formed on the product after evaporation was analyzed by means of scanning electron microscopy and X-ray photoelectron spectroscopy. The Silica-coated Alq3 and none-coated Alq3 were respectively used as the emitting layer to synthesis the binostructural electroluminescent devices of ITO/NPB (50nm)/Alq3 (50nm)/LiF(1nm)/Al (100nm) whose electroluminescent properties was then tested. Results show that the Silica-coated Alq3 exerts good morphology, and its thermal stability, film-forming and light colors make no difference to the none-coated Alq3. However, its life span was greatly improved which proves that the Silica-coated Alq3 serves as an effective coating technology.2. Liquid phase deposition method was employed to synthesize silica-coated Znq2 with sodium silicate as the silicon source and Znq2 the substrate matrix. The effect of different molar ratios of sodium silica to Znq2 on the coating result was analyzed by scanning electron microscopy under the conditions of fixed temperature and pH values. The thermal stability of the coating film as well as the electroluminescent characteristics of devices with silica-coated or none-coated Znq2 as the emitting layer was analyzed by thermal gravimetric analysis. Results show that the better coating result was achieved when the ratio of Na2SiO3 and Znq2 is 1/10, and the silica-coated lighting devices can contribute to prolong the lifetime of devices.3. Finally, the dissertation initially discussed the coating mechanism as well as the hydrolysis mechanism of sodium silicate and TEOS and give a preliminary interpretation to the experimental phenomena.Results show that the better coating result was achieved when sodium silicate as silicon source.

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