本論文將研究分為三大部分，皆針對共軛高分子於光電元件之應用作探討。在此選擇探討有機半導體的蕭基行為、高分子偏極化光二極體以及順向排列有機薄膜電晶體等三大課題。依序以不同專題對共軛有機分子於其中扮演的角色加以比較，分別敘述如下：
(1)不同摻雜物下之聚苯胺在金屬/半導體蕭基接面效應
聚苯胺蕭基行為的研究主要是針對摻雜硫酸(SA)與甲基磺酸(MSA)的不同，探討對於製作成蕭基二極體特性的影響。此兩種酸的特點為pH值相似但具有不同大小取代基之摻雜物。蕭基接面的製作是利用聚苯胺以電化學方法製備高分子膜於ITO玻璃上，再與低功函數的鋁箔進行接觸，製作出ITO/PANI (SA or MSA)/Al之蕭基二極體。電流-電位特性及交流阻抗分析來檢測高分子膜與金屬接面半導體參數，利用紫外光/可見光譜、循環伏安掃瞄及電子顯微鏡觀測來定義高分子膜的結構、成長速率、電荷移動動力機制。由於摻雜酸的不同，使得電子狀態、表面結構以及電荷傳輸機制的改變，以致元件接面電性，如勢壘高度、起使電位、Richardson常數及ideality factor有所差異。以電流-電位特性分析與交流組抗分析顯示，摻雜甲基磺酸的元件會有較薄的耗盡層厚度，以致於擁有較低的勢壘高度。
(2)高效率高分子偏極化光二極體
利用聚茀高分子(PF)經由配向後可得順向排列之結構，進而可發出藍色偏振光來進行研究。在此引入電洞傳輸配向層之觀念來改進文獻中傳統元件效率不佳亮度太低等缺點，以PVK之共軛高分子材料來當作配向層製備ITO/PEDOT/PVK/PF/Ca/Al之高分子偏極光二極體元件，除可增加電洞傳輸效果外亦可以保護電洞注入層PEDOT免於因摩擦而破壞表面。在此成功的得到效率為0.31 cdA-1非常接近標準元件的數值，並擁有超過1000 cdm-2以上之亮度及25左右之偏振比。以光致螢光及電致螢光光譜分析元件厚度對偏振效果之影響，發現電子電洞在結合區域與高分子鍊段重排區域必須重疊之重要性。在光譜中亦發現經由配向排列後所發出之偏振光具有紅位移，顯示出共軛鍊段增長的結果；以及出現較狹窄之半波寬，代表此元件具有光色較飽和之特性，此為順向排列降低分子排列的亂度，因而抑制部分分子鍊中相互吸引或振動的波峰所導致。
(3)順向分子排列之有機薄膜電晶體
在此引入配向層製備具規則性排列五環素(pentacene)當作主動層之有機薄膜電晶體，分別以ITO、金來當作閘極、源極與汲極，利用高分子PVP當作介電材料。探討不同共軛高分子以摩擦配向製備之配向材料(PF, PVK)對有機共軛分子排列性之影響，組裝成ITO/PEDOT/PVP/ (PF或PVK)/pentacene/Au之電晶體結構，以提升其載子遷移率。量測電流-電壓特性曲線求其載子遷移率、臨界電壓、電流開關比、飽和電流等參數並加以比較。以PF修飾後可將配向方向平行於通道電流方向之元件的載子遷移率提升至0.623 cm2V-1s-1，與標準元件相較有3倍的提升。且不同苯環位置(主鍊或側鍊)的共軛高分子鍊段，對於pentacene的排列亦有所影響，導致以PVK為配向層的載子遷移率反而下降。這也代表pentacene的分子排列與配向材料的選擇的確與元件的特性具有相當大的關係。

The main purpose of this dissertation is to study the application of conjugated polymers to optoelectronic devices. The investigations include three parts: the Schottky behavior of metal/semiconductor, polarized polymer light-emitting diodes, and thin film transistors. Conjugated polymers are utilized in each specific topic to investigate the role of active and modified layers. The brief descriptions of three parts in followings:
(1)Influence of dopant size on the Schottky behavior of polyaniline
Shottky diodes were fabricated with polyaniline (PANI) doped with sulphate anion (SA) and methane sulfonate anion (MSA) as Al/PANI (SA)/ITO and Al/PANI (MSA)/ITO devices. Schottky contacts could be established between PANI (SA or MSA) and aluminum foils which avoid tedious vacuum evaporation process in making contact. Thermionic emission model was found to fit with the current density (J)-voltage (V) characteristics of the diode. J-V curve and AC impedance characteristics were monitored for the devices. The values of the junction parameters such as ideality factor, barrier height and rectification ratio were compared. UV-vis spectra, cyclic voltammetric curve and scanning electron microscopy were used to define the polymer structure, growth rate and kinetic charge transport. The results are analyzed in the light of differences in dopability, morphology and mobility of carriers between SA and MSA doped PANI in forming Al/conducting polymer junction which alter the electronic state and influence Schottky properties of the device. PANI doped with MSA has thinner depletion layer that promote the probability of charge transport and results in lower barrier height.

(2)High luminescence polarized polymer light-emitting diodes
We have successfully constructed a polarized polymer light-emitting diodes (PLEDs) by employing poly(N-vinylcarbazole) (PVK) as an extra hole-transporting alignment layer that prevents the damage of the hole-injected layer of poly (3,4 ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT-PSS) by mechanical rubbing. The maximum luminance efficiency 0.31 cdA-1 of blue polarized PLED fabricated with the aligned polufluorene (PF) layer is obtained. The brightness approaches 1000 cdm-2 at a relatively low biased voltage. By using a PVK alignment layer, a dichroic ratio of 25.7 (at a 451 nm emission wavelength) was observed by finding the optimum thickness of PF. Herein, the most important topic is confirmed for the relationship between recombination area for hole and electron and rearrangement region in PVK/PF interface. The conjugated length of polymer chain in rubbed device thus longer than random ones and the energy band gap is reduced. This is lead to the red shift of the electroluminescence emission wavelength. The spectrum of photon emission is narrow, characterized by its full width at half maximum value, for the aligned PF film because the random vibrational motions of atoms inconjugated molecular chain were reduced.

(3)Pentacene-based thin film transistors with aligned layer of conjugated polymer
Pentacene-based organic thin-film transistors (OTFTs) with a dielectric layer of polyvinylphenol were fabricated onto the ITO glass substrate. Pentacene film was aligned parallel or perpendicular to the mechanical rubbing direction, which consisted with PF or PVK as alignment materials. Electronic parameters such as carrier mobility, threshold voltage and current on-off ratio are achieved. Improving the field-effect mobility in parallel rubbed device aligned by PF, with the value of 0.623 cm2V-1s-1, was achieved 3-fold by the standard pentacene-based OTFTs due to the highly ordered pentacene. The location of benzene ring for alignment layer in main chain or side chain affects the orientation of pentacene molecules, so the mobility of PVK aligned device is reduced. It indicates that field-effect carrier mobility is greatly depended on the molecular orientation, film roughness, and various conjugated alignment layers.

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