過鍍金屬氧化物於有機發光二極體中電洞注入層之研究

使用紫外光和X光激發光譜研究過渡金屬氧化物於有機發光元件中的影響。首先，在使用過渡金屬氧化物當作電洞注入層的有機發光元件，元件驅動電壓明顯的改善;在同樣到達電流密度4 (mA/cm2)的要求下，驅動電壓從原本沒有注入層的7.9 V，改進到5.4 V , 5.4 V, 5.8V and 6 V－分別對應到三氧化錸、七氧化二錸、三氧化鉬和氧化釕。而有氧化釕作為電洞注入層，最大亮度從2,200 (cd/m2)改進到3,300 (cd/m2)，足足改進了600%。但電流效率由5.1 (cd/A) 降到3.5 (cd/A).由實驗觀察，可能的解釋為，有了電洞注入層後，雖然改善了電流大小，但元件累積了過多的電荷在介面上，降低了效率。接下來，調查了蒸鍍溫度對於氧化鉬電性的影響，以及氧化鉬用於有機發光二極體的效用。較高蒸鍍溫度下對應到較高鍍率，氧化鉬膜比較接近於計量式三氧化鉬（MoO3），但對於它作為電洞注入層的效果反而變差了。反之亦同，當氧化鉬在較低的溫度下、較低鍍率蒸鍍時，有大量的額外能階狀態發現在禁止能隙中。這些額外能階狀態讓薄膜特性像一個高功函數的導體和一個有效電洞注入層，使電洞注入效果提昇。最後，調查七氧化二錸和三氧化錸的電性特性。七氧化二錸的額外能階狀態使其有更好得電洞注入表現。七氧化二錸的額外能階狀態源自於結構式中，錸氧之間的長鍵鍵結易斷裂有關。

關鍵字

過渡金屬氧化物；三氧化錸；七氧化二錸；三氧化鉬；氧化釕；紫外光激發光譜； X光激發光譜；有機發光元件；額外能階狀態

並列摘要

The mechanism of transition metal oxide, dirhenium heptoxide (Re2O7), rhenium trioxide (ReO3), molybdenum oxide (MoOx) and ruthenium dioxide (RuO2), used as interlayers in organic light-emitting devices (OLEDs) are investigated. The electronic structures and interfacial chemical reactions are investigated with ultraviolet and x-ray photoelectron spectroscopy. First of all, the influence of evaporation temperatures on the electronic structures of MoOx films and the electrical properties of organic light emitting diodes are investigated. MoOx films evaporated at a high temperature and a high deposition rate are close to a stoichiometric phase, but become less effective when they are used as a hole injection layer. However, when MoOx is evaporated at a lower temperature and a slower rate, there are large amounts of defect-related states present in the forbidden gap, which make the films behave like a high work function conductor and an effective hole injection layer. Second, the electronic structures of Re2O7 and ReO3 films in OLEDs are investigated. The gap states of Re2O7 interlayer due to the frailty of longer Re-O bond make the films behave as a better hole injection layer in OLEDs. Finally, the operation voltages at a current density of 4 (mA/cm2) decrease from 7.9 V to 5.4 V , 5.4 V, 5.8V and 6 V for OLEDs with 5-nm-thick ReO3 ,Re2O7, RuO2 and MoOx as interlayers, respectively. The maximum luminance is 13,300 (cd/m2) for the device with RuO2, compared to 2,200 (cd/m2) for the device without HIL. The maximum luminance value increases about 600% in OLED using RuO2. However, the performance of the current efficiency is 5.1 (cd/A) for the OLED without an HIL (ITO/TMO/NPB/Alq3/LiF/Al) and 3.5 (cd/A) for a similar device employing ReO3 as the HIL. We also investigate the accumulation of charge carriers as interfacial charges or dipoles at the interfaces of OLEDs.

並列關鍵字

transition metal oxide ； dirhenium heptoxide ； rhenium trioxide ； molybdenum oxide ； ruthenium dioxide ； ultraviolet and x-ray photoelectron spectroscopy ； organic light-emitting devices

參考文獻

2. H. Kanno, R. J. Holmes, Y. Sun, S. K. Cohen, and S. R. Forrest, Adv. Mater., 18, 339 (2006).

6. T. Lee, K. Lai, and L. Leung, Polymer (2009).

1. C. W. Tang and S. A. Vanslyke, Appl. Phys. Lett., 51, 913 (1987).

5. C. Adachi, T. Tsutsui and S. Saito, Appl. Phys. Lett., 56, 799 (1990).

9. S. Tokito and Y. Taga, Appl. Phys. Lett., 66, 673 (1995).

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過鍍金屬氧化物於有機發光二極體中電洞注入層之研究

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