Improving the Efficiency and Stability of Organic Light Emitting Diode Using [CuPc-Li-Al] Multilayer Cathode

Autor: Chih-Feng Sung, 宋志峰
Rok vydání: 2000
Druh dokumentu: 學位論文 ; thesis
Popis: 88
In this thesis, we will investigate the electrical and optical characteristics of the organic light emitting diode (OLED) devices using [CuPc-Li-Al] multilayer cathode. At first, we investigate the characteristics of CuPc for ITO/CuPc/TPD/Alq3/CuPc/Al structure and the characteristics of Li for ITO/TPD/Alq3/Li/Al structure. Then, we change the thickness of CuPc and Li for [CuPc-Li-Al] multilayer cathode of device structure ITO/TPD/Alq3/CuPc/Li/Al to study the operation mechanism and electrical and optical performance of OLED devices. Finally, we utilize x-ray photoemission spectroscopy (XPS) to investigate the CuPc/Li interface formation. Concerning to the study of the properties of CuPc and Li, we can observe that CuPc layer treats as anode buffer layer for ITO/CuPc/TPD/Alq3/Al structure can enhance luminous efficiency. But CuPc layer is used for cathode buffer layer for ITO/TPD/Alq3/CuPc/Al choosing Ca, Mg or Al as cathode, the optical performances become very poor. If we select Li as cathode for ITO/TPD/Alq3/Li/Al structure, we must control the thickness of Li layer under 1nm to obtain good optical characteristic. If the thickness of Li layer is over 1nm, the device would fail very soon. Furthermore, we try to change the thickness of CuPc and Li for [CuPc-Li-Al] multilayer cathode to study the device performance. In the condition of CuPc-17nm, Li-2nm, we can observe the best electrical and optical performance. We utilize XPS to investigate the reasons about above results. It attributes to the reaction of Li with CuPc to produce new composition but a part of CuPc still preserve their original property. And the new interface formation will improve the electron injection efficiency greatly. Although, the other low work function metals such Ca or Mg also can react with CuPc. However, the property of CuPc would be affected. Therefore, the optical performance 100 times poorer than the device with Li layer. The conclusion of this study reveals that the electron injection efficiency of OLED devices are not mainly attributed to the choice of low work function metals. It attributes to the interface formation and the influence of metal materials for organic materials.
Databáze: Networked Digital Library of Theses & Dissertations
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