| Summary: | 博士 === 國立成功大學 === 電機工程學系碩博士班 === 101 === Transparent conducting substrate is an important research and development topic in applications of organic light emitting devices. Although ITO (indium tin oxide) is probably the most successful transparent conductive oxide (TCO) thin film, however, indium is a relatively scarce element in the earth. Thus, the cost for ITO production is more expensive than that of others. Besides, the toxic nature of indium could be hazardous to human and environment. For the purpose of overcoming these ITO basically drawbacks, new type ZnO-based materials have been actively studied by many research groups in recent years. The transparent conductive ZnO-based thin films are investigated as an alternative to ITO films. In contrast to ITO materials, the ZnO material is more stable in reduction ambient, nontoxic, and the abundance of its constituent elements makes it available at a low cost. Therefore, ZnO-based thin films have attracted much attention as the transparent electrode.
Highly transparent conducting Al-doped zinc oxide (AZO) films were deposited on a non-alkali glass substrate and flexible poly (ether sulfone) (PES) substrates by an RF magnetron sputtering system at room temperature and under low sputtering power. Without substrate heating or post-annealing treatment, ZnO-based flexible electrodes with low resistivity and high transmittance were prepared. In this work, electromechnical study was conducted on the performance of Al-doped zinc oxide film deposited on a flexible PES substrate. The change in electrical and optical properties by using a simple model method with face-out (FO) bending and face-in (FI) bending was proposed to understand the failure mechanisms. The results of bending test show that the face-out direction enables AZO films deposited on PES substrates to tolerate greater mechanical bending.
Then, a hole-only device was used to explore charge behavior at the interface between anode materials and the organic layer. Hole-only devices with AZO film and commercial ITO anodes were used to examine the efficiency of hole injection and its effect on performance of OLEDs. OLED devices with AZO and ITO anode materials, respectively, were also fabricated to verify experimental results. The dependence of hole injection and OLED performance on the anode material was determined. We also reported that AZO films of various thicknesses were prepared by sputtering on glass substrates for use as transparent anodes of OLED devices. The effect of AZO film thickness with and without heated substrates on the performance of OLEDs based on AZO anodes was investigated.
Finally, we present Ti-doped ZnO (TZO) as transparent anodes of OLEDs for high work function. Our results demonstrated that the resistivity and transparency of TZO was slightly worse than those of AZO, but TZO showed a superior performance to AZO due to its high work function. These new transparent conducting thin films are helpful for the development and practical applications of organic electronic devices.
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