高效率有機發光元件之元件結構及電極結構研究

Device and Electrode Architectures for High-Efficiency Organic Light-Emitting Diodes

卓庭毅(Ting-Yi Cho)

指導教授 ： 吳忠幟

國立臺灣大學/電機資訊學院/電子工程學研究所/博士(2007年)

https://doi.org/10.6342/NTU.2007.00985

摘要

由於有機材料其本身的獨特性，適合應用於高效率、大面積的全彩顯示面板及照明用白光光源，因此近年來逐步受到各方的矚目，並吸引廣泛的研究。在本論文中針對有機發光元件中之元件結構及材料介面進行深入的研究及探討，尋求元件效率之改善。
本論文利用光學模型分析堆疊串接式有機發光元件中之光學結構，並結合微共振腔結構與堆疊串接式結構，大幅提昇元件之正向發光效率。在元件光學結構之分析中，我們瞭解將堆疊串接元件中的各發光單元分別製作在反節點，可極大化元件之發光效率。若更進一步利用微共振腔結構之效應，適當設計元件之光學結構，則可製作出超高效率(200 cd/A)之上發射型綠色燐光有機發光元件。
本論文提出一超薄堆疊串接型有機白光元件結構，係利用不同波長的光其反節點位置不同的特性，將黃光及藍光分別製作於各自的第一反節點，而得以在維持原發光效率的前提之下，減少元件整體厚度，進而降低操作電壓及提升元件能量轉換效率之目的。
本論文研究一金屬氧化物材料--氧化鉬作為有機發光元件中之電洞注入層。氧化鉬具有較低的製程溫度、高導電能力、及平坦的膜層表面，適合在有機發光元件中應用。使用氧化鉬作為注入層之元件，可大幅降低陽極介面的電洞注入能障，且可廣泛通用於具有不同功函數之電極材料，論文中也更進一步利用紫外線光譜分析技術(UPS)深入研究其中原因，並提供一合理解釋。
最後，本論文利用先前所發展之芴寡聚物材料作為有機發光元件中之電子傳導層。此高能隙材料具有高雙載子移動率、高熱穩定性之優異特性，故具有簡化製程、增加元件操作壽命的潛力。論文中廣泛嘗試各種優化陰極介面之材料與製程方式，發現氟化銫(CsF)可有效提高電子注入能力並改善元件之能量轉換效率，也同時採用了UPS探討其成因並提供解釋。

關鍵字

有機發光元件 ； 高效率 ； 為共振腔 ； 垂直串接 ； 導電性摻雜

並列摘要

Organic light-emitting devices (OLEDs) have attracted much attention for its applications in high-efficiency, large-scale, full-color flat-panel displays and solid-state lighting. In this thesis, we focused on developing device structures and electrode structures to obtain improvement of emission efficiency of OLEDs.
We investigated theoretically and experimentally the optical characteristics of noncavity and microcavity tandem OLEDs. By use of rigorous electromagnetic modeling of OLEDs, radiation characteristics of tandem OLEDs as a function of device structures are analyzed and correspondingly the guidelines for optimizing performances of tandem devices are suggested. Making use of the analysis results, we show that with well designed microcavity conditions and device structures, a five-fold enhancement in luminance can be achieved with cavity tandem devices having only two emitting units. A very high efficiency of 200 cd/A has been demonstrated with a phosphorescent cavity two-unit device.
We demonstrated ultra-thin tandem WOLEDs by locating yellow and blue emitters at corresponding first antinodes to the metal electrode, instead of 1st and 2nd antinodes in conventional tandem OLEDs. This attempt leads to the substantial reduction of operating voltage improvement in power efficiency, compared to conventional tandem WOLEDs. Besides, it shows stable EL spectra under various bias conditions.
The thermally evaporated molybdenum oxide (MoOx) was investigated as the effective hole-injection material for organic light-emitting diodes (OLEDs). The use of MoOx significantly lowers the operating voltage of OLEDs. According to ultraviolet photoemission spectroscopy (UPS), there exists gap states in MoOx layer, such that the Fermi level is pinned and hole-injection barrier through MoOx layer is reduced. As such, OLEDs using MoOx as the hole-injection layer are rather insensitive to the anode materials utilized.
Finally, we investigated the derivative of oligofluorene, ter(9,9-diarylfluorene), as an efficient electron-transport layer in OLEDs. In interface engineering of the cathode, we found that the introduction of CsF effectively reduces the electron injection barrier. Combined with high mobility of oligofluorene (i.e. electron-transport layer), the operating voltage of OLEDs can be reduced and power efficiency is improved accordingly.

並列關鍵字

OLED ； high-efficiency ； microcavity ； tandem ； conductive doping

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