噻吩系列共軛高分子在正規和可拉伸場效應電晶體中結構與性能的關係

Abstract

半導體高分子已經廣泛地運用在薄膜式場效應電晶體、太陽能電池與記憶體元件上，得利於共軛高分子的特性，使其在製備上價格低廉，且可利用溶液製程大面積處理，在機械性質上，更具有可撓曲的特質，隨著化學合成學術的發展，導電高分子結構設計也受到了高度關注。本論文目標在於系統性統整出以四噻吩為主幹的高分子衍生物，建構其結構與化學物理性質、正規還有拉伸元件效能間的關係。 本文的第一部分(第二章)，噻吩共軛聚合物衍生物的正規場效應電晶體，一系列共九隻高分子成功被開發出，藉由這些高分子可以同時比較酯基取代(PBTBO、PDCBT)、併環噻吩(PDCBT、PDCTT)、酯基取代基位置(PDCTT、PDCBT-TT)、雙軸延伸(PDCTT、PDCTT2T)以及氟基團引入的影響。PDCBT-F 具有最佳之載子遷移率0.365cm2V-1s-1，同時保持足夠高的開關電流比值還有較低的電壓閥值。酯基的引入可以限制烷基側鏈擺動方向，提升薄膜排列規整度，進而提升載子遷移率；併環噻吩的改變，會表現出更佳的共平面性，但也因為較近的分子內作用力，造成測鏈彎曲，在電性上稍微降低；酯基取代基位置會有不同程度的自由度，PDCBT-TT 具有較多自由空間，造成嚴重的噻吩扭轉，破壞了面內方向排列，影響了電晶體表現；雙軸延伸在主鏈形成螺旋結構增大了面外方向排列的間距，阻礙了面內方向的堆疊，電性上有較差的結果；氟基團的加入提升了所有高分子的剛性，僅有PDCBT-F 在結晶上出現雙峰取向(bimodal orientation)，其餘高分子顯示出較差的結晶結果。 本文的第二部分(第三章)，噻吩共軛聚合物衍生物的本質拉伸、轉印場效應電晶體，共三隻材料(PDCBT、PDCTT、PDCBT-F)因其較高的載子遷移率，而被選擇做為本章節的研究對象。PDCBT 具有最佳的綜合表現，經過轉印、拉伸破壞回到最初狀態後，保有36%載子遷移率(相對於純轉印)。PDCTT 和PDCBT-F 在整體上較為剛硬，拉伸破壞更加明顯，研究結果也指出，拉伸方向對電性也有很大影響，垂直方向的電性平均較平行方向來的高。最後的重複拉伸測試，PDCBT 在垂直方向有維持0.1 cm2V-1s-1 的載子遷移率、近0V 的閥值電壓、大於104 的開關電流比。

Semiconductor polymers have been widely used in thin film field-effect transistors, solar cells and memory components due to the characteristics of conjugated polymers which are low-cost in process, large area solution process and even stretchability. With the development of chemical synthesis in academy, the design of conductive polymer structure has also received great attentions. The aim of this thesis is to systematically integrate the relationship between its structure to chemical, physical properties, and the performance of regular and stretchable devices in quaterthiophene-based polymer derivatives. 1. Regular Field-Effect Transistors of Thiophene-Based Conjugated Polymer Derivatives In chapter 2, a series of nine polymers have been successfully developed. These polymers construct the influence of carboxylated group substitutions (PBTBO, PDCBT), fused-thiophene (PDCBT, PDCTT), carboxulated substituent sites (PDCTT, PDCBT-TT), biaxial extension (PDCTT, PDCTT2T) and fluorine group introduction. PDCBT-F has highest charge carrier mobility of 0.365 cm2V-1s-1. It maintains a sufficiently high on/off current ratio and a lower voltage threshold. The introduction of the carboxylated group can limit the swing of the alkyl side chain, improve the polymer arrangement, and thereby improve the mobility; The fused-thiophene will show better coplanarity, but a bending side chain due to closer intramolecular force, slightly decreases to electric properties; The position of the carboxylated substituent has different extent of degree of freedom. For higher one (PDCBT-TT), it causes severe fused-thiophene twist, destroys the in-plane alignment and affects the transistor performance; The biaxial extension forms a spiral structure in the main chain which increases the spacing in the out-of-plane direction, hindering the stacking in the in-plane direction result in low mobility. The addition of the fluorine group enhances the rigidity of all the polymers. But only PDCBT-F exhibits bimodal orientation, the remaining polymers show poor crystallization results. 2. Intrinsically Stretchable and Printable Field-Effect Transistors of Thiophene-Based Polymer Derivatives In chapter 3, a total of three materials (PDCBT, PDCTT, PDCBT-F) were selected for the study of this chapter due to their high charge carrier mobility in pristine. PDCBT has the best overall performance. It retains 36% charge carrier mobility (relative to 0% strain applied) after 100% stretching and releasing back to origin. PDCTT and PDCBT-F are relatively rigid structure to PDCBT. The damage by stretching/printing is more obvious. The results indicate that the direction of stretching has an evident effect on electrical properties. The average charge mobility measured in the perpendicular direction is higher than the parallel direction. PDCBT show a 0.1 cm2V-1s-1 charge carrier mobility, near 0V threshold voltage, and large enough on/off ratio (>104) in perpendicular direction under mechanical durability test.