位置規則性-聚(3-烷基噻吩)之合成與特性探討及其應用於有機場效電晶體之研究

STUDIES ON THE SYNTHESIS AND CHARACTERIZATION OF REGIOREGULAR POLY(3-ALKYLTHIOPHENE) AND APPLICATION ON ORGANIC FIELD-EFFECT TRANSISTOR

張怡鳴(Yi-Ming Chang)

指導教授 ： 郭欽湊

大同大學/工程學院/化學工程學系所/碩士(2004年)

摘要

位置規則性-聚(3-烷基噻吩) (regioregular poly(3-alkylthiophenes))為一以頭對尾(head-to-tail)方式進行偶合(coupling)排列之共軛高分子，可輕易地達到一個低能量、低空間障礙的共平面構造，具有高度的共軛性、較佳的導電度及光學性質，並能產生自我組裝(self-assembly)之絕佳結構，有利於光電元件之應用，如有機場效電晶體(organic field-effect transistor, OFET)。
本研究成功利用GRIM (Grignard metathesis)法合成具有不同側鏈烷基長度之高位置規則度( > 90% )-聚(3-烷基噻吩)，經分析後發現，其物理與化學性質受不同位置規則度與側鏈烷基長度影響甚鉅。UV-visible光譜顯示，聚(3-烷基噻吩)會隨著位置規則度的提高產生紅位移，產生較高之共軛性。由XRD結果指出，聚(3-烷基噻吩)擁有絕佳之排列與結晶性結構，並與SEM結果相互比對後可知，較高之位置規則度有利於聚(3-烷基噻吩)之成膜性。此外，聚(3-烷基噻吩)之熱穩定性與熔點會隨著位置規則度的增加與側鏈烷基長度的減少而有所提升，整體而言，位置規則性-聚(3-烷基噻吩)於400℃氮氣環境下可擁有一良好之熱穩定性。
本研究中，同時對位置規則性-聚(3-烷基噻吩)之有機場效電晶體性能進行探討，其場效位移率(field-effect mobility)會受到材質之不同烷基長度及不同成膜程序而產生改變。研究結果指出使用側鏈烷基長度較短之聚(3-烷基噻吩)為材質製備有機場效電晶體，可擁有較高之場效位移率。在成膜程序上，可利用降低高分子溶液濃度或使用高沸點溶劑之方式，如甲苯，來提升電晶體之開關電流比(on/off current ratio)。此外，研究中提出幾種方法可提升位置規則性-聚(3-烷基噻吩)場效電晶體之位移率，第一為利用HMDS試劑對元件之二氧化矽表面進行處理；第二為利用退火(anneal)處理將聚(3-烷基噻吩)層重新排列；而第三為使用滴落塗佈(drop-cast)方式，使位置規則性-聚(3-烷基噻吩)順向垂直排列沉積於元件表面，產生高結晶性。在經最佳化成膜製程後，以位置規則度96% 之聚(3-己烷基噻吩) (poly(3-hexylthiophene))製作之有機場效電晶體，場效位移率最高可達3 × 10 - 2 cm 2 / Vs，而開關電流比於VDS = VG = - 100 V時為2 × 10 2。

關鍵字

位置規則性 ； 聚(3-烷基噻吩) ； 場效電晶體 ； 導電性高分子

並列摘要

Regioregular head-to-tail poly(3-alkylthiophene) (HT-P3AT), containing only head-to-tail coupling, can be easy of access a low energy, low space obstacle coplanar conformation, leading to highly conjugated polymer. HT-P3AT possess better conductivity and optical properties, and can undergo self-assembly, resulting in highly ordered three-dimensional polymer architecture. And these materials have a significant practical impact in optoelectronic application - organic field-effect transistor (OFET).
The high level of regioregularity (> 90%) of HT-P3ATs with different length of the alkyl side chains can be synthesized successfully by GRIM (Grignard metathesis) method. It is found that the physical and chemical properties of HT-P3ATs are significantly affected with different level of regioreularity and length of the alkyl side chains. UV-visible spectra of HT-P3ATs show that the red shift of λmax increases with increasing the level of regioregularity, resulting in a higher degree of conjugation. XRD results indicate that HT-P3ATs have a great order and crystalline structure, and corresponding SEM photographs show that higher regioregularity is good for film-forming properties of HT-P3ATs. In addition, the thermal stability and Tm of HT-P3ATs increase with increasing the degree of regioregularity and decreasing the length of the alkyl side chains. In summary, all HT-P3ATs exhibit an excellent thermal stability under 400℃ in nitrogen atmosphere.
In this study, the performance of HT-P3AT field-effect transistor (HT-P3AT FET) has been investigated. The field-effect mobility of HT-P3AT FETs can be changed with different length of the alkyl group of materials and various film-forming processes. Results indicate that use shorter alkyl side chain of HT-P3ATs as material to fabricate OFET has higher field-effect mobility. In term of the film-forming processes, the on/off current ratio of HT-P3AT FET can be increased as the concentration of polymer solution reducing or using the high boiling point solvents such as toluene. In addition, the field-effect mobility of HT-P3AT FET can be improved by some methods. The first method is the SiO2 surface of device modify by HMDS reagent. The second method is reordering the HT-P3A layer via the annealing treatment. The third method is making HT-P3ATs oriented vertically (standing upright) on the device’s surface by the drop-cast method, leading to highly crystalline polymer. Through the optimal condition of the film-forming process, the maximum field-effect mobility of OFET fabricated with 96% regioregularity of head-to-tail poly(3-hexylthiophene) achieve 3 × 10 - 2 cm 2/Vs with an on/off current ratio of 2 × 10 2 at VDS = VG = - 100 V.

並列關鍵字

conducting polymer ； field-effect transistor ； poly(3-alkylthiophene) ； regioregular

參考文獻

2.T. Ito, H. Shirakawa and S. Ikeda, J. Polym. Sci., Polym. Chem. Ed., 12 (1974) 11.

3.H. Shirakawa, E. J. Louis, A. G. MacDiarmid, C. K. Chiang and A. J. Heeger, Phys. J. Chem. Soc. Chem. Commun., (1977) 579.

6.M. G. Kanatzidis, Chem. Eng. News, 3 (1990) 3.

8.Nobel Symposium in Chemistry: Conjugated Polymers and Related Materials: The Interconnection of Chemical and Electronic Structure, W. R. Salaneck, I. Lundstrom and B. Ranby, Ed’s (Oxford Sci., Oxford, 1993)

14.A. O. Patil, A. J. Heeger and F. Wudl, Chem. Rev., 88 (1988) 183.