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研究生:劉原良
研究生(外文):Yuan-liang Liu
論文名稱:有機發光二極體在Al/LiF界面的研究
論文名稱(外文):Study on the Al/LiF interfaces of the organic light-emitting diodes
指導教授:翁恆義
指導教授(外文):Uerng-Yih Ueng
學位類別:碩士
校院名稱:國立中山大學
系所名稱:電機工程學系研究所
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2004
畢業學年度:92
語文別:中文
論文頁數:79
中文關鍵詞:Al/LiF有機發光二極體
外文關鍵詞:OLEDAl/LiF
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在本論文中,將討論陰極與有機層的界面特性。由許多文獻中,可了解由陰極與有機層界面形成的dipole 層將決定有機發光二極體的特性。而由柯達公司所發表的Al/LiF/Alq3 的架構中,最主要是由於置入的LiF 將改變Al/Alq3 之間界面特性,原因是LiF 改變了Al/Alq3 的化學反應使得界面dipole 使真空能階移動更大進而降低電子注入能障和增加OLED 性能,而且發光效率增加也顯示出Al/LiF/Alq3 沒有gap state 產生與相互擴散。

在文獻中的元件模型對於載子注入是經由兩個步驟,第一歩載子先由金屬的費米能階跳躍至界面處的能態分佈中,第二歩載子由界面處的能態跳躍至有機層中。隨後,在有機層以跳躍(hopping)的方式移動。本論文將針對LiF 的厚度變化對於注入模型的影響,並假設在LiF 為0.5nm時元件會有最佳表現,而我們認為LiF 會在Al/LiF/Alq3 的界面中分解出Alq3-與Li+離子,並且兩分解出的離子量相同,而在LiF 層間也將形成一壓降,其模擬結果與實驗結果是一致的,當厚度越大其元件特性越差,一般認為當厚度大於0.5nm 時,元件特性越差,因為LiF 為絕緣層,所以LiF 太厚載子將難以注入至有機層。
In this present paper, the electrical characteristics of the interface between the cathode and organic layer in OLEDs are discussed. The dipole formed between the cathode and organic layer are the dominant factor resulting in the electrical characteristics of OLEDs. However, based on the Al/LiF/Alq3 architecture published by the Kodak company, it is mainly because that by inserting a LiF layer lead to change the interface characteristic of Al/Alq3 as to changed the chemical reaction occurred at the interface of Al/Alq3. The LiF interlayer could enable the contact interface being depolarized and the work function being close to the vacuum level, therefore, it will reduce the electron injection barrier to improve the OLED performance. In addition, the increase luminous efficiency was due to that without generating any gap state and interdiffusion occur at the interface of Al/LiF/Alq3.

For the carrier injection model reported by several authors, the carrier injection process is summarized by two steps as follow: first, the inject carriers translate from metal Fermi level to the energy distribution of interface. Second, inject carriers translate from the energy distribution of interface to the energy distribution of organic layer, afterward, the inject carriers migrate with hopping conduction in the organic level. Hence, it will regards to the dependence of the variety of LiF thickness on the influence of the injection model, and assume that as LiF thickness is 0.5 nm the device could be able to have the best performance, and also assume that LiF was able to decompose equal number of Alq3- and the Li+ ions at the interface of Al/LiF/Alq3 contact, and that led to form a voltage in the LiF layer. Finally, we found that the simulation approaches were consistent with the experimental results very well.
目 錄

中文摘要…………………………………………………………………i
英文摘要…………… …………………………………………………ii
目錄……………………………………………………………………iii
表目錄……………………………………………………………………v
圖目錄……………………….…………………………………………vi

第一章 序論……………………………………………………………1
1.1 簡介…………………………………………………………………1
1.2 平面顯示器的發展…………………………………………………2
1.3 有機發光材料的分類與小分子與高分子的比較…………………3
1.4 研究動機..............................................6

第二章 有機發光二極體理論基礎……………...……………….…7
2.1 螢光與磷光………………………….………...…………………7
2.2有機發光元件的基本原理.................................8
2.3 發光效率理論的極限…………………......……………………8
2.4 多層結構.............................................10
2.4.1 單層有機發光元件...................................10
2.4.2 雙層有機發光元件...................................10
2.4.3 多層有機發光元件...................................11
2.5 全彩化...............................................12

第三章 陰極與有機層界面與分析…………....................14
3.1電極改善……………………………………………………………14
3.1.1單一金屬電極…………………………………………….….…14
3.1.2合金金屬電極…………………………………………......…15
3.1.3置入一層buffer layer………………………………………..15
3.2 陰極與有機層之界面分析……………………………………….16
3.2.1 Interface Dipole………………..……………………..….16
3.2.2金屬擴散至有機層……………………….…………….………20
3.2.3 Gap state……………………………………………….….…21
3.3 Al/LiF之UPS與XPS分析………………….………….……..….22

第四章 注入模型……………………………………………………..27
4.1電子傳導途徑…………………………...….……………………27
4.2 Bulk limited current……………………………………….…27
4.2.1無陷阱的SCLC(space charge limited current)………....28
4.2.2有陷阱的SCLC(space charge limited current)……....…28
4.3 Injection limited current……………………………………29
4.4 LiF厚度變化對於injection limited current model之修正.35
4.5 討論.................................................37

第五章 結論………………………………………………………..…39
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