高分子摻雜於有機發光二極體之應用; Doping in Polymers for Organic Light Emitting Diodes

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题名:	高分子摻雜於有機發光二極體之應用;Doping in Polymers for Organic Light Emitting Diodes
作者:	張興華;Xing-Hua Zhang
贡献者:	光電科學研究所
关键词:	有機發光二極體;高分子摻雜;有限摻雜源之染料擴散熱轉印法;OLEDs;Doping;Finite-source dye-diffusion therm
日期:	2001-07-18
上传时间:	2009-09-22 10:23:15 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	由小分子及高分子製作成的光電顯示元件或光電元件中, 摻雜是一項重要的技術。為了調制發光顏色及增強元件的效率，在小分子有機發光元件與高分子有機發光元件中常使用發光性的摻雜材料。為了元件結構的多樣性及在一片基板上做多元件的整合，需要將摻雜材料作橫向及縱向的分布的調制。由真空沉積方法所做成的小分子元件中，橫向摻雜的調製可由切換式的陰影遮罩達成，而縱向調製可用順序式的共蒸鍍完成。然而由甩膜塗布的方法所做成的高分子元件中，傳統的摻雜的方式只能將摻雜材料在薄膜作均勻的分布而無法在橫向及縱向上做調制。在這本論文中，我們利用有限摻雜源之染料擴散熱轉印法(Finite-source dye-diffusion thermal transfer，FS-D2T2) 可對已形成之高分子薄膜進行橫向局部的摻雜以及縱向摻雜的控制。在進行FS-D2T2時，將被轉印膜與轉印源薄膜直接緊密接觸，透過加熱擴散的方式，使染料轉印至被轉印膜。我們分別在poly(N-vinylcarbazole) (PVK)或poly (N-vinylcarbazole): 2-(4—biphenyl)-5-(4-tert- butylphenyl)-1,3,4-oxadiazole (PVK: PBD)的系統中進行了一連串的染料擴散實驗，而且證明可利用Fick’s擴散理論來模擬染料的擴散行為。另一方面在有機蒸氣的環境中，摻雜染料在低於高分子的玻璃轉換溫度下即能做有效的擴散。此效應使得高玻璃轉換溫度的高分子及更多的的摻雜材料能用於有限摻雜源之染料擴散熱轉印法。利用有限摻雜源之染料擴散熱轉印法方便調控的特性，我們可對高分子中的摻雜材料做橫向及縱向的調制。在橫向的調制中，用來做高分子有機發光元件色彩的整合而達到製作多彩元件的目的。而在縱向的調制中，利用摻雜材料的淺摻雜分布可降低摻雜材料的載子陷阱效應。另一方面在本論文中還提出一可填充式的熱轉印方法，以容許重複使用D2T2的熱轉印源。為了獲得低驅動電壓及高效率的元件，需要增進電荷注入的能力。一個有效的方法是對有機半導體薄膜作導電性摻雜。在本論文的最後，我們探討利用SbCl5對高分子PVK 作導電性摻雜，並將其用為有機發光元件中之電洞注入層。我們發現摻雜了SbCl5的PVK可大幅增進電洞自陽極注入有機層的能力。 Doping is an important technology for electronic imaging and optoelectronic devices based on molecular or polymeric materials. Emissive doping is usually used for tuning emission colors and enhancing luminescence efficiency. For the versatility in the device structures and the integration of different devices on a substrate, it usually requires the capability to laterally and vertically modulate the distribution of dopants in organic films. In molecular devices fabricated by vacuum deposition, lateral modulation of compositions can be implemented by switchable shadow masking, and vertical modulation is achieved by controlling the co-deposition sequences. However, in organic devices incorporating molecularly doped polymers (MDPs), the conventional blending process can only produce uniform dispersion of dyes throughout the polymer layer, providing no spatial selectivity of dopant distribution. In this thesis, we propose finite-source dye-diffusion thermal transfer (FS-D2T2) for performing controllable doping of polymer films. In this process, the polymer receiver film is placed in direct contact with the dye-dispersed polymer donor film to permit direct dye-diffusion thermal transfer. We perform a series of experiments of dye diffusion in the poly(N-vinylcarbazole) (PVK) or the poly (N-vinylcarbazole): 2-(4—biphenyl)-5-(4-tert- butylphenyl)-1,3,4-oxadiazole (PVK: PBD) matrix systems and show that it can be modeled by Fick’s diffusion theory. We have also shown that in an atmosphere of organic solvent vapor, effective dye-diffusion thermal transfer may be enhanced at temperatures much below Tg of host glassy polymers. Such an effect may permit polymers of higher Tg and wider ranges of dye molecules to be used in the D2T2 process for electronic imaging applications. By using finite-source dye-diffusion thermal transfer process , we demonstrate lateral and vertical modulation of dopant distribution in polymer films. Lateral modulation of dopant distribution was applied to the color integration of OLED devices. Vertical modulation of dopant distribution was used to reduce carrier trapping effect caused by the emissive dopants in the device. To permit repeated use of the D2T2 source plate, a method of rechargeable thermal transfer stamping was also introduced. Furthermore, we demonstrated the enhancement of device performance with small molecule/FS-D2T2 doped polymer hybrid heterostructures. In order to achieve low driving voltage and high efficiency in OLED devices, it is necessary to facilitate the injection of charges. One effective approach to enhance carrier injection is to conductively dope the organic layer. In this thesis, we investigated the SbCl5-doped PVK as a conductively doped polymer, and its use as a hole-injection material in OLEDs. It is found that SbCl5-doped PVK is an effective hole-injection material for both polymer or small-molecule based OLED devices.
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