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  • 學位論文

噻吩系列共軛高分子中側鏈結構對於電荷/離子傳輸之影響

The Side-Chain Effects of Thiophene-based Conjugated Polymers on the Charge/Ion Transport Property

指導教授 : 闕居振

摘要


至今,有機半導體材料因為其價格低廉、溶劑項製程、高度可調整性、輕量化及可撓曲性等優點而被廣泛應用於有機場效電晶體、有機發光二極體、有機太陽能電池、有機電化學電晶體以及記憶體。早期,科學研究主要圍繞噻吩展開,然後後期發現D-A設計有助於電荷分離以及擁有更好的光電性質,逐漸噻吩的發展開始脫離主流。然而,噻吩共軛高分子因為其合成上的難度較低,使得商業化上有更高的潛力,仍然有許多科學家對噻吩共軛高分子持有抱負。 在這篇碩論中,我們引入不同側鍊嫁接在噻吩共軛高分子上,改善噻吩共軛分子的光電、電化學性質,從結果而言,我們可以肯定側鍊改質是一項有效的策略,進而幫助噻吩共軛高分子性質改善。 本文的第一部分(第二章),我們引入不同拉電子官能基,分別是酯基以及醯胺基進入複合環噻吩共軛高分子。我們實行了光電性質、分子模擬、表面研究、場效電晶體等實驗,證明酯基可以透過穩定構型提升噻吩共軛高分子主鍊的平面性,如上述優點,P1擁有比較好的結晶性以及電荷傳遞。然而P2在側鍊間有很強的偶極分布,引來很強的聚集效應,降低了結晶性。從場效電晶體的表現而看,P1有著1.19 x 10-2 cm2 s-1V-1的電子遷移率,而P2僅1.48 × 10-5 cm2 s-1V-1的電子遷移率,將近一千倍的差距。另外,因為P1呈現更低的能階,我們還檢定了P1的元件穩定性,P1保持了30天的元件表現。總結而言,由兩種拉電子基引起迥異的偶極分布,造成高分子材料在電子傳輸上有很大的差別。 本文的第二部分(第三章),我們在噻吩共軛高分子主鍊以及乙二醇側鍊中引入不同的中間體,分別是酯基及碳原子。藉由上一個計劃所學習到的結論,我們深信酯基可以減少因為離子引入所造成的立障。至此,我們研讀了光電、電化學表現,可以從電致變色測量中觀測到,含有乙二醇的高分子在離子嵌入上,有巨大的優勢,除此之外,從循環伏安法量測中可以發現,含有酯基的高分子在電容上有明顯的區別,顯示具有較高的電荷儲存能力。基於此,我們完成了高分子的基本鑑定,接下來我們會進行元件的製造以及量測,進而比較實際上在OECTs上的表現。

並列摘要


To date, organic semiconducting materials aroused great in electrochemical and optoelectronic applications because of advantages of low cost, solution process, highly-tunable, light weight, and stretchability. Rapid development of organic field-effect transistors (OFETs), organic light-emitting diodes (OLEDs), organic solar cells (OSCs), organic electrochemical transistors (OECTs) and memristors witness the tremendous successful of organic materials application. Early, most research were focus on polythiophene conjugated polymers (PTs). Recently, researchers turn to D-A design polymers because of push-pull effect and superior optoelectronic performance. However, PTs still attracted intense research interests because of their facile synthesis compared to other conjugated polymers. Herein, we applied different side chain into PTs to improve optoelectronic and electrochemical performance, the results showed that side chain engineering is effective in the fields of organic conjugated polymer. 1. Electron-Withdrawing Function Group Side-Chain Substitution for Thiophene-based Conjugated Polymers: Carboxylate Ester Group versus Carboxamide Group In Chapter 2, we investigate and compare the side-chain substitution effects of two electron-withdrawing side chains, the carboxylate ester and the carboxamide groups, for a thieno[3,2-b]thiophene (TT)-based PT. Comparative studies including optical and electrical characterizations, molecular simulation, morphology, and transistor performance, are conducted. The results show that the carboxylate ester side chain enables the backbone to adopt a centrosymmetric conformation and induces a push-pull effect on the backbone. As a result, its derived polymer (P1) possesses a higher crystallinity and a superior intra-charge transfer (ICT). Whereas, the carboxamide side chain imposes a larger torsion on the backbone. Besides, it brings in a strong intramolecular dipole moment (μmz) along the side chain direction. It results in more intense aggregation but with lower crystallinity. Finally, P1 (with carboxylate ester side chain) and P2 (with carboxamide side chain) deliver dramatically different hole mobility (μh) values (1.19 x 10-2 and 1.48 × 10-5 cm2 s-1V-1), showing ~1000 times difference. In addition, owing to the strong electron-withdrawing ability of the carboxylate ester group, P1 owns deep-lying energy levels and this enables air-stable mobility. The μh of the P1 device shows negligible changes when storing in air for 30 days. Collectively, our result shows that two electron-withdrawing side chains exhibit distinctly different dipole moment directions that results in distinct charge transport properties. 2. Ions Injection Improvement and Backbone Modification of Thiophene-based Polymers In Chapter 3, we investigated the effect of different spacer bridged thiophene-based backbone with ethylene glycol side chain. Carboxylate ester group and carbon atom were introduced between ethylene glycol side chain and thiophene-based backbone as spacer. Comparative studies including optical and electrical characterizations are conducted to elucidate the electrochemical performance difference of these polymers.

參考文獻


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