喹喔啉電子施體-受體高分子半導體之合成、性質鑑定及其光電元件應用

Quinoxaline-Based Donor-Acceptor Semiconducting Polymers: Syntheses, Properties, and Optoelectronic Device Application

賴美秀(Mei-Hsiu Lai)

指導教授 ： 陳文章

國立臺灣大學/工學院/化學工程學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.00903

摘要

高分子半導體近來由於其在發光二極體、薄膜電晶體和光伏打電池的廣泛應用而備受矚目；共軛高分子為被廣泛研究之高分子半導體，它具有可調控的光電性質和良好的可加工性，因此擁有極佳之應用潛力。本論文主要目的在由實驗合成出一系列不同電子施體和受體 (在本研究中為喹喔啉) 所組成的共軛高分子，進行薄膜電晶體和光伏打電池元件的製備與測試。

在本研究第一個部分 (第二章)，五種含有側鏈經修飾的喹喔啉 (quinoxaline) 構成施體-受體或施體-受體-施體結構的共軛高分子，包poly[2,5-didecyloxy-1,4-phenylene-alt-2,3-bis(4-(2-ethyl hexyloxy)phenyl)-5,8–dithien-2–yl-quinoxaline](POC10DTQ(EHP)), poly[2,5-didecyloxy-1,4-phenylene-alt-2,3–bis(4-(2-ethylhexyl oxy)phenyl)-5,8–dithien-2–yl-quinoxaline] (PFODTQ(EHP)), poly[thiophene-2,5-diyl-alt-2,3-bis(4-(2-ethylhexyloxy)phenyl)-5,8-quinoxaline] (PThQx(EHP)), poly[thiophene-2,5-diyl-alt-2,3-bis(4-(2-ethyl hexyloxy)phenyl)-5,8-dithien-2–yl-quinoxaline] (PThDTQ(EHP))和poly[2,3-bis(4-(2-ethylhexyloxy)phenyl)-5,8–dithien-2–yl- quinoxaline] (PDTQ(EHP))。由於高分子內之施體的HOMO能階和受體的LUMO能階混層，使其整體HOMO-LUMO間的能隙為非線性關係之縮小，進而得到較低能帶隙的產物。這些高分子 (除PThDTQ(EHP)外) 可溶於常見的有機溶劑中。從吸收光譜圖和循環伏安法鑑定測得能隙在1.57 ~ 1.92 eV和1.93 ~ 2.14 eV此範圍；其中PThQx(EHP) 因為由較強的電子施體(thiophene)構成且有最平衡的受體比例，故有最小的能隙。另外，此五種共聚高分子在氯苯溶劑中製備成薄膜電晶體，測得之電洞遷移率間於 4.34×10-3 ~ 4.7×10-5 cm2V-1s-1，on-off ratio範圍為103 ~ 104；由於PDTQ(EHP)可形成極平坦而均勻的薄膜，可能是此高分子有最佳之電洞遷移率的主因。再對PFODTQ(EHP)，POC10DTQ(EHP) 和PThQx(EHP) 做太陽能元件測試，光能轉換效率分別達到 1.76 %，0.64% 和0.92 %。

本研究第二部分(第三章)利用Suzuki反應成合成五種以咔唑 (carbazole)為施體，具有長短側鏈基的喹喔啉以及其兩側接有噻吩的分子等單體做為受體的共軛高分子，包括Poly[3,6-(2-ethylhexyl) carbazole-alt-2,1,3-benzothiadiazole] (PCzBTD), Poly[3,6-(2-ethylhexyl)carbazole-alt-2,3-dimethyl-5,8-quinoxaline] (PCzDQ), Poly[3,6-(2-ethylhexyl)carbazole-alt-2,3–dimethyl -5,8–dithien-2–yl-quinoxaline] (PCzDTQ), Poly[3,6-(2-ethylhexyl)carbazole-alt-2,3-bis(4-(2-ethylhexyloxy)phenyl)
-5,8-quinoxaline] (PCzQx(EHP)) 和Poly[3,6-(2-ethylhexyl) carbazole-alt-2,3-bis(4-(2-ethylhexyloxy)phenyl)-5,8–dithien-2–yl- quinoxaline] (PCzDTQ(EHP))等五種。這些高分子以有長側鏈的喹喔啉組成者溶解度較好，產物分子量較大且可溶於常見的有機溶劑中。從吸收光譜圖和循環伏安法得到此系列高分子之能隙在1.91 ~ 2.37 eV 和1.63 ~ 2.34 eV此範圍；而PCzDTQ(EHP)有最小的能隙是由於其分子內較有效的電荷轉移。另外五種高分子裂解溫度皆在400oC以上，展現了良好的熱穩定性。由UV-visible光譜的偏移可發現長側鏈的喹喔啉不僅改善產物溶解度，同時也增加了系統的有效共軛強度。綜合說來，本論文結果證實了電子施體-受體和主鏈結構對共軛高分子的電子和光電性質影響的重要性，亦佐證此類高分子於光電元件應用之潛力。

關鍵字

共軛高分子 ； 薄膜電晶體 ； 太陽能電池

並列摘要

Semiconducting polymers have been paid great attention because their intensive application of light-emitting diodes, thin film transistors, and photovoltaic devices. The conjugated polymer is a class of semiconducting polymers under intensive research, because it owns tunable optoelectronic properties and good processibility, leading to great potential of device application. The main objective of this thesis is to synthesize a series of conjugated polymers composed of different electron donors and acceptor (mainly quinoxaline) for the fabrication and measurement of field effect transistors and photovoltaic cells.

In the first part of this thesis (Chapter 2), five side-chain modified quinoxaline-containing conjugated copolymers with donor-acceptor or donor-acceptor -donor structures were synthesized and characterized, including poly[2,5-didecyloxy- 1,4-phenylene-alt-2,3–bis(4-(2-ethylhexyloxy)phenyl)-5,8–dithien-2–yl-quinoxaline] (POC10DTQ(EHP)),poly[2,5-didecyloxy-1,4-phenylene-alt-2,3-bis(4-(2-ethylhexyl oxy)phenyl)-5,8–dithien-2–yl-quinoxaline] (PFODTQ(EHP)), poly[thiophene-2,5-diyl-alt-2,3-bis(4-(2-ethylhexyloxy)phenyl)-5,8-quinoxaline] (PThQx(EHP)), poly[thiophene-2,5-diyl-alt-2,3-bis(4-(2-ethyl hexyloxy)phenyl)-5,8-dithien-2-yl-quinoxaline] (PThDTQ(EHP)), and poly[2,3bis(4-(2-ethylhexyloxy)phenyl)-5,8-dithien-2-yl- quinoxaline] (PDTQ(EHP)). The hybridization of the high-lying HOMO energy level of the donor and low-lying LUMO energy level of the acceptor could produce a relatively small band gap polymer. The synthesized polymers (except PThDTQ(EHP)) are soluble in common organic solvents. Their band gaps are in the range of 1.57 ~ 1.92 eV and 1.93 ~ 2.14 eV measured by optical spectra and cyclic voltammetry, respectively. PThQx(EHP) has the smallest band gap because it is composed of the donor (thiophene) with higher electron-donating ability with the balanced percentage of the acceptor among the analogous polymers. These copolymers were fabricated into thin film transistors by their chlorobenzene solutions and measured their hole mobility in the range of 4.34×10-3 ~ 4.70×10-5 cm2/(Vs) with on/off ratios in the order of 103 ~104. The smooth and homogeneous surface of PDTQ(EHP) film may be a main factor for the highest charge carrier mobility. Furthermore, the solar cell power conversion efficiencies based on polymers PFODTQ(EHP), POC10DTQ(EHP) and PThQx(EHP) achieved 1.76%, 0.64% and 0.92%, respectively.

In the second part of this thesis (Chapter 3), five different carbazole-based copolymers were synthesized by palladium(0)-catalyzed Suzuki coupling reaction, including poly[3,6-(2-ethylhexyl)carbazole-alt-2,1,3-benzothiadiazole] (PCzBTD), poly [3,6-(2-ethylhexyl)carbazole-alt-2,3-dimethyl -5,8-quinoxaline] (PCzDQ), poly[3,6-(2-ethylhexyl)carbazole -alt-2,3-dimethyl-5,8–dithien-2–yl-quinoxaline] (PCzDTQ), poly[3,6-(2-ethylhexyl)carbazole-alt-2,3-bis(4-(2-ethylhexyloxy)phenyl)-5,8-quinoxaline] (PCzQx(EHP)) and poly[3,6-(2-ethylhexyl)carbazole-alt-2,3-bis (4-(2-ethylhexyloxy) phenyl)-5,8-dithien-2-yl-quinoxaline] (PCzDTQ(EHP)). The polymers containing quinoxaline with long alkoxy-phenylene side chains have better solubility, resulting larger molecular weights and meanwhile soluble in common organic solvents. Their optical and electrochemical band gaps were measured in the range of 1.91 ~ 2.37 eV and 1.63 ~ 2.34 eV, and the effective intramolecular charge transfer should account for the smallest band gap of PCzDTQ(EHP). Furthermore, by the red shifts of UV-visible spectra, we found that the alkoxy-phenylene side groups of quinoxaline both improve the solubility and enhance the effective conjugation length. In sum, the present study suggests the importance of donor/acceptor strength and backbone structure on the electronic and optoelectronic properties of conjugated polymers, and also demonstrated the potential on optoelectronic device application of these polymers.

並列關鍵字

quinoxaline ； conjugated polymer ； thin film transistor ； solar cell

參考文獻

3. Yang, Y.; Heeger, A. J. Nature 1994, 372, 344.

4. Sirringhaus, H.; Tessler, N.; Friend, R. H. Science 1998, 280, 1741.

5. Babel, A.; Jenekhe, S. A. J. Am. Chem. Soc. 2003, 125, 13656.

9. Roncali, J. Chem. Rev. 1997, 97, 173.

11. Kwon, O.; McKee, M. L. J. Phys. Chem. A 2000, 104, 7106.