過渡金屬氧化物於掺雜有機半導體之研究

Studies of Organic Semiconductors Doped with Transition Metal Oxides

林昌廷(Chang-Ting Lin)

指導教授 ： 吳志毅

國立臺灣大學/電機資訊學院/光電工程學研究所/博士(2008年)

https://doi.org/10.6342/NTU.2008.01209

摘要

由於近期有機電子產品可商業化於顯示器或是發光照明上及還在開發的有機太陽能電池，因而受到許多學者的參與研究。最常見到的有機電子元件即是有機發光二極體 (Organic Light Emitting Diodes, OLEDs)。其基本結構裡都含有n型掺雜的電子注入或傳輸層與p型掺雜的電洞注入或傳輸層。其作用是來幫助載子從電極注入到有機層及提高元件本身的導電度並降低元件操作電壓。本論文一開始即是藉著導入掺雜的無機物半導體的一些物理概念延伸到掺雜的有機物半導體中。其中像是費米能階(Fermi level)及蕭基能障(Schottky Barrier)的概念。藉著這些觀念來幫助我們了解有機半導體。而之後會提到有機半導體中n型掺雜及p型掺雜的原理介紹。最後著重討論一種新型的p型的掺雜物，過渡金屬氧化物，氧化鉬MoO3。從實際元件效率及紫外光電子能譜激發術 (ultraviolet photoemission spectroscopy, UPS) 和 X光電子深層電子能階譜激發術 (x-ray photoemission spectroscopy, XPS) 這兩種技術討論氧化鉬應用於元件的原理與機制。我們發現到共蒸鍍電洞傳輸層NPB與MoO3,將會使元件電性獲得大幅改善。甚至單只用一層MoO3放置在陽極與NPB之間，元件本身操作電壓也會下降。同時，當使用MoO3放置在不同陽極與NPB之間，電性會趨於一致。也利用UPS證實出此種現象即是費米能階釘札(Fermi level pinning)所產生的效應。而後我們也發現到應用薄金屬搭上MoO3的組合，也可以有效的應用在其他相關的有機電子元件結構來增進元件效率。總結此論文探討了無機與有機掺雜半導體間的基本特性，介紹了兩者掺雜機制的不同。同時也實例用Cs2CO3、F4-TCNQ、MoO3等三種掺雜物材料探討其中於OLEDs裡掺雜的原理與應用。

關鍵字

有機發光二極體 ； 光電子能譜激發術 ； 有機表面科學

並列摘要

Organic semiconductors have attracted lots of attentions, such as Organic Light Emitting Diodes (OLEDs), polymer LEDs , organic solar cell, and organic TFT. The typical OLEDs are multilayer structures, which consist of an anode, an anode buffer layer, hole injection layers (HIL), a hole transport layer (HTL), an emitting layer (EML), an electron transport layer (ETL), an electron injection layer (EIL), and a cathode. In order to decrease the Schottky barrier height to achieve Ohmic contact. OLEDs structures must have doped transport layers by appropriate choices of n-type and p-type doping materials.
In the beginning of this dissertation, we will discuss two kinds of doped semiconductors, inorganic and organic, and explain the p-type and n-type doping effect in both kinds of doped semiconductors. We will also discuss metal/organic and metal/inorganic interfaces with energy band diagrams explanations. Simultaneously, we try to understand organic semiconductors easily by similar concepts analogous to inorganic semiconductors such as the Fermi level and Schottky barrier. We then discussed the mechanisms of enhanced hole-injection in OLEDs with p-type dopant, MoO3 (a kind of transition metal oxide). UPS (ultraviolet photoemission spectroscopy) and XPS (x-ray photoemission spectroscopy) spectra show that MoO3 would catch electrons from NPB and cause p-type doping in NPB. We further investigation the interactions between low work function metals and MoO3, low work function metals would easily get O atoms from MoO3, resulting in the transition to MoO2 and the increase in conductivity at the same time. Finally, we have investigated that there will always be gap states in the forbidden gap of MoO3 after depositing MoO3 onto different substrates including ITO, Au, Al, Ag, and Mo. UPS shows that there is Fermi level pinning effect of metal/MoO3 structures.

並列關鍵字

OLED ； Photoemission Spectroscopy ； organic surface science

參考文獻

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