- 學位論文
聚(3-己烷基噻吩)靜電紡絲纖維在場效電晶體上之應用與形態分析
Morphology and Application of Electrospun Poly(3-hexylthiophene) Nanofibers on Field-effect transistor
摘要
奈米結構的半導體高分子具有應用在軟性光電元件的潛力。然而其在製備方式、形態控制上仍有許多探討空間。在本篇論文中，我們以P3HT為內管PMMA為外管的雙軸系統，再去除外管的方式來製備純的P3HT奈米纖維，並研究製程參數(外管流速、內管溶劑和迴火溫度)對其型態和電性的影響。其分述如下： 1. 外管流速對聚(3-己烷基噻吩)雙軸靜電紡絲纖維在場效電晶體上之應用與形態分析(第二章): 本研究藉由改變雙軸系統中的外管流速，來探討流速對靜電紡絲的構型與場效電晶體電性的影響。再去除外管PMMA後，純的P3HT奈米纖維在不同流速下直徑分別為168 nm(0.5 ml/hr), 131 nm(1.0 ml/hr), 257 nm(1.5 ml/hr) and 520 nm。由於噴絲時所使用的是具有穩定噴絲系統的高沸點氯苯，故纖維表面非常平滑且均勻。由其形態結果來看當外管流速小時，P3HT的結晶度和結晶大小有明顯被提升的效果，且在不同流速下其載子移動率有103的差異。在流速為1.0 ml/hr下載子移動率可高達1.92*10^-1 cm2/V s。此明顯的差異可歸功於流速小時單位流體所受的電場強度較強，使高分子鏈可充分被電場拉伸，產生具有方向性的排列方式。此結果初次提供P3HT靜電紡絲內高分子鏈堆疊和電性的研究，並且提出一簡易方式來改變其載子移動。 2. 內管溶劑和迴火溫度對聚(3-己烷基噻吩)雙軸靜電紡絲纖維在場效電晶體上之應用與形態分析(第三章): 這部分是在固定外軸條件下來改變系統中的內管溶劑(氯仿, 氯苯 and 1, 2, 4-三氯苯)，進而調控纖維內部的型態和其電性。結果顯示內管溶液的黏度和其中高分子的堆疊程度為影響靜電紡絲纖維內部高分子型態的主因。低黏度的氯仿系統裡，溶液在電紡的過程中容易受到電場拉伸，因此有較高的分子鏈順向性。即使高分子結晶度受到抑制，其載子移動率仍可高達3.57*10^-1 cm2/V s。結果顯示對於P3HT靜電紡絲來說，分子鏈的順向性對載子傳遞的影響性更勝結晶度。本文的最後一部分為將第二章中外管流速 1.0 ml/hr的部分以不同溫度進行熱處理，並且探討纖維內部的型態和其電性。由SEM和XRD觀察出熱處理有助於分子鏈於纖維內部的排列，並且進而提高高分子結晶度。然而當溫度高於100 ℃時，過高的分子流動性反而破壞電紡的幾何侷限性，導致經電紡產生的分子鏈順向性被破壞，因此在電性表現上熱處理溫度在100 ℃時有最高的載子移動率。由以上結果顯示靜電紡絲所提供的幾合侷限性有助於載子於一維結構中傳遞，且對P3HT靜電紡絲纖維來說，100 ℃為其型態變化的轉折點。 目前的研究結果顯示製程參數對於靜電紡絲P3HT纖維的型態和場效電晶體元件特性具有很重要的影響。
並列摘要
Semiconductor based polymer nanostructures have potential applications in flexible electronic or optoelectronics, such as nanowire or nanofiber. The fabrication, morphology control, and electronic properties of electrospun nanofiber remain significant challenge. In this thesis, we used two-fluid coaxial electrospinning technique to prepare P3HT/PMMA core/shell polymer nanofiber, followed by extraction of PMMA to obtain pure P3HT nanofiber. The morphology and electronic properties of the prepared nanofiber show the enhanced carrier mobility through the optimization of process parameters, as described below: 1. Effects of Shell Flow-Rate on the Morphology and Electrical Properties of Coaxial Electrospun Poly(3-hexylthiophene) Nanofibers For Field-Effect Transistor(chapter 2): The P3HT fiber diameters after removing the shell PMMA were 168, 131, 257 and 520 nm using the different shell flow rates of 0.5, 1.0, 1.5, and 2.0 ml/hr, respectively. All of the above ES fibers are smooth and uniform because the electrospun solvent chlorobenzene with a high boiling point leading to more stable cone-jet model during ES process. The morphology studies show that the π-π stacking, crystallinity and crystal size of P3HT were significantly enhanced at the shell flow rate was reduced, which led to large charge-carrier mobility. The highest charge-carrier mobility as the shell flow rate of 1.0 ml/hr could be up to 1.92*10^-1 cm2/Vs. The higher electrical force along fiber axis at low shell flow rate probably induced preferred orientation of P3HT polymer chains in nanofiber and promoted the already-aligned polymer chains folding to be the better crystallinity and larger crystal size after annealing treatment. A schematic representation on the relationship between chain packing and charge transport in ES P3HT nanofiber is also provided in this chapter. 2. Effects of Solvent and thermal treatment on the Morphology and Electrical Properties of Coaxial Electrospun Poly(3-hexylthiophene) (P3HT) Nanofibers For Field-Effect Transistor (chapter 3): In this study, three different core solvents, chloroform(CF), chlorobenzene(CB), and 1, 2, 4-trichlorobenzene(TCB), were employed to manipulate the morphologies and electrical properties of ES P3HT nanofibers. The results show that the core solution viscosity plays an important role to control the morphology and charge-carrier mobility. In the lower viscosity solutions using chloroform, polymer chains completely extend can be fully stretched by electrical force, resulting in higher ordered orientation and charge-carrier mobility of the P3HT nanofiber even though processing lower crystallinity and thinner crystal size. On the other hand, the high solution viscosity using TCB led to the significant P3HT aggregation in solution but poor orientation within the nanofiber, leading to low carrier mobility. The highest charge-carrier mobility of prepared ES P3HT nanofiber based FET using chloroform system could be up to 3.57*10^-1 cm2/Vs, which suggest the importance of ES process on preferred orientation of polymer chains within fibers. The morphology and electrical properties were also investigated by thermal treatment at different temperature Morphology studies using SEM and XRD demonstrate that the thermal treatment decreases in the fiber diameter, increased P3HT crystallinity and affected carrier mobility. However, as temperature was higher than 100 ℃, the geometrical confinement begin to be destroyed, resulting in poor orientation within nanofiber, thereby decreasing the measured field-effect mobility. Our observations show that both the orientation and crystallinity affect the mobility and 100 ℃ is an optimum temperature of thermal treatment to prepare ES P3HT nanofiber FET. The present study addressed the importance of the process parameters on the morphology and OFET device characteristics of the ES P3HT nanofiber.