有機發光二極體被認為是目前有機會作為大面積、全彩，平面化顯示器之元件，由於它具有一些優點如：製程簡易、高應答速度、高對比、輕、薄及應用便利等。因此，許多研究探討改善其元件結構之及了解其操作機制。本研究利用增加載子注入效率以及採用特殊元件結構調整載子的特性來改進整體元件之效率。
首先我們將各種不同的超薄緩衝層熱蒸鍍於ITO基板上並予以紫外光臭氧處理，藉此來探討其對於元件載子注入特性的影響。利用X射線和紫外線光電子光譜儀來測定其功函數以及使用表面能量化來研究其接面特性。當緩衝層厚度以及紫外光臭氧處理時間最佳化後，元件的驅動電壓降低、電流效率與最大亮度增加且同時可消除共振穿隧效應。能帶、表面能以及表面極性的量測指出利用紫外光臭氧處理過之超薄緩衝層來同時提高ITO之功函數與表面特性可大幅的提升元件之表現。
再來，我們將改進元件的結構來調變載子於元件內的再結合與傳輸特性。首先我們採用兩種不同型態(陷阱式與阻擋式)的量子井結構來平衡正負載子的數量，陷阱式量子井擁有較佳的效果，可大幅的提升元件效率達36%，並可減輕於高壓操作下效率驟降的效應。此外共主體結構被採用來侷限載子再結合區域以提升整體元件效率，利用電洞傳輸材料(NPB)與藍光發光材料(p-DMDPVBi)以最佳比例(20/80)混成共主體發光層，並搭配橘光摻雜體(Rubrene)即可製做出高效率白光元件。能帶圖、螢光光譜、吸收光譜、電激發光譜以及空間電荷量測則被使用來探討此二種結構的背後物理機制。結果顯示量子井與共主體結構為簡易且有效增進元件效率的方法。

Organic light-emitting diodes (OLEDs) are currently considered as promising candidates for large-area, full-color and flat-panel displays due to their prominent advantages such as easy fabrication and convenient use in applications. A lot of effort has, therefore, been made to improve device structures and to understand their operating mechanisms. This thesis focuses on improving the device performance by using the anode ultra-thin buffer layer, quantum-well and co-host structure.
At first part of this thesis, various ultra-thin buffer layer film was thermally deposited between ITO and NPB as the buffer layer and then treated with the ultraviolet (UV) ozone, then the fabrication of organic light emitting diodes (ITO/buffer layer/NPB/Alq3/LiF/Al) to study its effect on hole-injection properties. Work function was estimated from X-ray photoelectron spectroscopy, and surface properties were calculated from measured contact angles using water and CH2I2 as test liquids. With optimized buffer layer thickness, device performance such as turn-on voltage, current efficiency and maximum luminance are significantly improved. Moreover, eliminate the resonant tunneling effect. Measurements of energy band, surface energy and surface polarity indicated device improvement came from the simultaneous increase in work function and surface energy of ITO by adding treated ultra-thin buffer layer film between ITO and the hole-transporting layer.
Secondly, device structures are modified to manipulate the carrier characteristics of transporting and recombination. To investigate two different types of multiple-quantum-well (MQW) structure on emission characteristics of white organic light-emitting diodes (WOLEDs), we fabricate trapping-type and blocking-type MQWs by inserting C545T (green dye) and TPBi, respectively, into hole transport NPB layer (ITO/CuPc/NPB/MADN:rubrene/TPBi/LiF/Al). Bright efficient and stable fluorescent white emission was obtained for the OLED with 2 trapping-type MQWs formed with C545T (thickness: 2 nm). The device current and power efficiency were greatly raised 36% relative to that of reference device. Furthermore, the improvement remained even beyond the roll-off effect caused by high current density. Besides, efficient co-host emission layer has been demonstrated by mixing blue-emitting p-DMDPVBi and hole-transporting NPB in optimal weight ratio (w/w = 80/20). First, efficiency enhancement was observed in the fabrication of blue organic light-emitting diodes (ITO/NPB/p-DMDPVBi:NPB/TPBi/LiF/Al). Then, bright, efficient and stable fluorescent white organic light-emitting diodes (WOLEDs) were obtained by doping the optimal co-host emissive layer with orange dye (rubrene). The device performance was significantly improved. The all improvement mechanisms were elucidated using energy level diagrams, photoluminescence spectra, absorption spectra, electroluminescence spectra and SCLC measurement. Current results show that forming the trapping-type MQW structure and the co-host emission layer are promising ways to improve device performance, making it applicable for facile fabrication of efficient OLEDs.

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