含側鏈共軛基團嵌段共聚高分子之合成、性質鑑定及其記憶體元件應用

Block Copolymers with Pendant Conjugated Chromophores: Syntheses, Properties, and Memory Device Application

林佩萱(Pei-Hsuan Lin)

指導教授 ： 陳文章

國立臺灣大學/工學院/高分子科學與工程學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.10251

摘要

近幾年來，側鏈含有共軛基團之共聚高分子已引起了廣泛的研究與應用。相較於主鏈共軛的線性高分子而言，側鏈含有共軛基團之共聚高分子擁有較佳的溶解度、可調控的型態以及可精準控制地光電性質。然而，關於不同的高分子結構、電荷傳導和光電性質對於記憶體元件上的應用尚未被深入研究。本論文主要目的在由實驗合成出共聚高分子側鏈含有不同共軛基團系列，並進行記憶體元件的製備與測試。
在本研究第一個部分 (第二章)，主要是利用原子轉移自由基聚合法和鈴木偶聯反應合成新穎性側鏈含有共軛基團之共聚高分子，而共軛基團包括3,5-difluorophenyl, fluorene 和 pyrene等三種。我們所成功合成出的共聚高分子已藉由凝膠滲透層析儀與氫核磁共振光譜鑑定之。所合成高分子之分子量皆在一萬以上且溶於常見的有機溶劑如氯仿、四氫呋喃和氯苯中。由吸收光譜圖可看出此類共聚高分子之吸收峰隨著共軛基團含量增加而往長波長位置位移，由光學吸收值計算可得此系列高分子之能隙在3.14 ~ 4.11 電子伏特；由螢光光譜的紅移可發現摻入不同比例之共軛基團可以有效改變發光峰之峰值。側鏈共軛結構和團塊比例對高分子的電子和光電性質之影響在本研究中作完整的分析。
本研究第二部分 (第三章) 即使用第一部份所合成之共聚高分子製備成記憶體元件。此類型共聚高分子以三種不同的團塊比例組成，其分別為 3:1，1:1和1:3 (聚苯乙烯:側鏈共軛基團)。記憶體元件的構造是將高分子薄膜夾在兩層電極之間的三明治結構，其上層電極是鋁，而下層電極是氧化銦錫。對於側鏈基團為3,5-difluorophenyl的記憶體元件系統中，其元件物理機制是受到燈絲理論影響，因為在全對數電流-電壓圖分析中，在開啟狀態時之曲線斜率約等於1.0。另外，在pyrene共軛基團元件系統中，在通一電場後，聚苯乙烯的絕緣性質可進行電洞的捕捉，而側鏈pyrene基團則會自發性地進行電洞載子的傳輸，因而形成揮發性記憶體。而最後一個例子則是側鏈部分為fluorene基團，因其高分子本身之最高填滿軌域狀態和氧化銦錫的工作程式相差甚大，導致電洞不易進行傳導，故呈現絕緣性質。本研究建立高分子之化學結構與電子結構對元件之關係，而本論文使用之含有側鏈共軛基團之共聚高分子在記憶體元件上之應用上極具發展潛力。

關鍵字

共聚高分子 ； 側鏈共軛基團 ； 記憶體元件

並列摘要

A wide range of vinyl monomers and their polymers bearing various conjugated chromophores have been extensively studied and applied in recent years. In contrast to wholly π-conjugated linear polymers, non-conjugated polymers containing pendant π-conjugated moieties systems are of interest for their advantages of excellent solubility, tunable morphology and precisely optoelectronic properties. However, the correlation between polymer architecture, charge transport and photophysical properties in the switching behavior of memory devices have not been fully explored yet. Therefore, this thesis mainly focuses on the synthesis and characterizations of polymers with pendant conjugated moieties combined with their applications on memory devices.
In the first part of this thesis (Chapter 2), atom transfer radical polymerization (ATRP) and Suzuki coupling reaction were applied to synthesize the new non-conjugated diblock copolymers with different pendant conjugated chromophores, including 3,5-difluorophenyl, fluorene and pyrene groups. The targeted diblock copolymers were successfully synthesized and characterized by gel permeation chromatography (GPC) and 1H NMR spectrum. All the polymers have number average high molecular weight (>104) with polydispersity index (PDI) of 1.2 ~ 1.4, and soluble in common organic solvents such as chloroform, THF and chlorobenzene. The shifted absorption band of these diblock copolymers were shown as the increasing pendant conjugated moieties, and the band gaps calculated from absorption edge are in the range of 3.14 ~ 4.11 eV. Furthermore, adding pendant conjugated moieties to copolymers would shift the λmaxabs to longer wavelength in fluorescence spectra. Effects of side-chain chromophores structures and ratios on the optoelectronic and electrochemical properties were systematically investigated.
In the second part of this thesis (Chapter 3), the new non-conjugated diblock copolymers based on polystyrene derivatives containing pendant 3,5-difluorophenyl, pyrene and fluorene groups were used to evaluate the memory applications. The prepared diblock copolymers are composed of three different block ratios of 3/1, 1/1 and 1/3 (polystyrene/pendent chromophores). The bistable memory behavior is conducted by a simple sandwich device configuration consisted of spin-coated polymer film between indium-tin oxide (ITO) bottom electrode and aluminum (Al) top electrode. For the pendant 3,5-difluorophenyl series of memory devices, the mechanism of the switching behavior is based on filamentary conduction, because the logarithmic plot of the I-V data for the ON state contains a linear region with a slope of 1.0. In the case of pyrene based polymers, the insulating characteristics of polystyrene could be served as hole-blocking moieties and provide the charge trapping environment. Thus, the pendant pyrene based polymers exhibit the electrical volatile nature which attributed to the back transferring of shallow trapped charges in the pendant functional groups. And for the last case of the devices with fluorene moieties, its insulating behaviors are due to the higher energy level between the work functions of the ITO bottom electrode and the HOMO level of the active polymer layer, which might prevent the hole injection process. The relationship between the chemical structure, electronic properties, and device performance were also established in this study.

並列關鍵字

Block copolymer ； Pendant conjugated chromophores ； Memory device

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