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  • 學位論文

具有雙軸延伸結構之噻吩半導體材料:合成、形態鑑定與場效電晶體之應用

Thieno[3,2-b]thiophene-based Semiconducting Materials with Biaxially Extended Side Chains: Synthesis, Morphology and Organic Field-Effect Transistor Applications

指導教授 : 陳文章

摘要


有機共軛半導體材料因其低廉、環境友善的製程、可伸縮撓曲的性質與可大面積製造等優點,使其在工業上與學術上皆被廣泛的研究著。其中含有噻吩並噻吩的共軛高分子與小分子,因噻吩並噻吩剛硬的平面性結構,使其能形成高度規則的結晶。近幾年來,具有雙軸延伸結構之共軛側鏈半導體系統,其延伸的共軛長度可增加電荷載子傳輸能力、吸收光譜範圍、水氧穩定性與場效電晶體的表現。在本研究當中,將合成一系列具有雙軸延伸結構之噻吩並噻吩半導體材料並對其形態鑑定與場效電晶體之特性加以探討,其細節如下: 1. 具有雙軸延伸結構之噻吩並噻吩共軛高分子之形態鑑定與場效電晶體之應用 (第二章): 一系列的具有雙軸延伸結構之噻吩並噻吩(2DTT)高分子,包括 PT2DTT、PV2DTT、P2T2DTT、PTT2DTT與PDTT2DTT 藉由微波聚合器,利用Stille coupling成功的合成。在這一系列高分子中,對於導入不同未取代共軛單元之高分子的化學結構、光電性質與場效電晶體特性逐一討論。所有的高分子皆表現出良好的熱穩定性與水氧穩定性,然而結構的不同,對場效電晶體的特性產生很大的影響。在X-光繞射的分析中,在PT2DTT與PDTT2DTT觀察到較小的晶面距離,然而PT2DTT主鏈的嚴重扭曲與 PDTT2DTT的低溶解度,縮短了有效共振的長度與降低成膜性,導致較差的場效電晶體特性。在PV2DTT中,導入的乙烯基使得高分子的層狀結構變得較為鬆散,而拉大其晶面距離,且因其不佳的水氧穩定性,使得PV2DTT在場效電晶體表現無法有效提升。當導入噻吩並噻吩做為未取代共軛單元時,強共平面性的噻吩並噻吩共軛單元使得PTT2DTT晶面距離有效縮短,因此展現出較佳的場效電晶體特性。在P2T2DTT中,使用兩個噻吩做為未取代共軛單元,其結構模擬出的主鏈平面性與在X-光繞射中發現的結晶性層狀排列結構,使得P2T2DTT的場效電晶體擁有高達0.359 cm2 V-1 s-1的電洞遷移率,同時具有良好的電流開關比達7.1×106。這些結果說明了具有雙軸延伸結構的共軛高分子系統能藉由導入不同的未取代共軛單元改變其光電性質、結晶形態與場效電晶體的特性,同時噻吩並噻吩的系統能有效的提升結晶性與電荷遷移的能力,展現出其在有機光電元件應用的能力。 2. 具有雙軸延伸結構之噻吩並噻吩共軛小分子材料之形態鑑定與場效電晶體之應用(第三章):以2DTT為主的雙軸延伸小分子材料,藉由Stille-coupling與Suzuki reaction導入不同的取代基 (T與2T),探討化學結構、光電性質與場效電晶體特性的影響。2DTT為主的小分子材料皆表現好的水氧穩定性,其最高佔有分子軌域能階皆低於-5.39eV。在這一系列的小分子材料中,不同的共軛長度對於小分子的結晶形態有很大的影響。T-2DTT-T 這隻小分子材料展現出了高達0.0347 cm2 V-1 s-1的電洞遷移率,同時具有良好的電流開關比達1.2×107,當增加其共軛長度時,2T-2DTT-2T的電洞遷移率大幅下降至6.69×10-5 cm2V-1s-1。如此劇烈的差異主要來自於兩種共軛小分子的結晶結構,在原子力顯微鏡的觀察下,T-2DTT-T主要以長達500 nm大小的晶粒連續性的層狀排列著,然而2T-2DTT-2T卻是不連續的排列,不僅晶粒較小,晶界也較多。在X-光繞射分析中,2T-2DTT-2雖然因為延伸的共軛長度,成功的縮短晶面距離,然而T-2DTT-T卻表現出更強更明顯的晶面繞射。因為晶粒形態與結晶性的差異,使得兩種小分子在場效電晶體上的表現大不相同。這些結果可以證明具有雙軸延伸的小分子材料可藉由導入不同的共軛單元,改變結晶形態與場效電晶體之性質。

並列摘要


Recently, biaxially extended conjugated systems with conjugated side chains have been developed to enhance charge transport, air stability as well as their OFET device performance1,2 while conjugated polymers and oligomers with thieno[3,2-b]thiophene moieties have been reported to promote formation of highly ordered crystalline domains.3,4 In this research, a series of 3,6-bis(5-dodecylthiophen-2-yl)thieno[3,2-b]- thiophene (2DTT)-based biaxially extended conjugated thiophene semiconducting materials were synthesized and investigated. The details of explorations are summarized as below: 1. Synthesis, Optoelectronic Properties and Organic Field-Effect Transistors of Thieno[3,2-b]thiophene-Containing Polymers With Biaxially Extended Side Chains (Chapter 2): A series of 2DTT-based polymers, including PT2DTT, PV2DTT, P2T2DTT, PTT2DTT and PDTT2DTT have been synthesized by Stille coupling under microwave heating. All the studied polymers exhibited stable thermal properties. Incorporating 2DTT with different spacers also has dramatic influence in structure and FET performance. Although a smaller d-spacing observed in XRD, PT2DTT and PDTT2DTT exhibit poor FET performance. The optimized geometry of PT2DTT indicates a severe torsion in polymer backbone and adopts poor film qualityeven spin-coated with chloroform. On the other hand, PDTT2DTT unfortunately bears low solubility and is only slightly soluble in processing solvent. When a vinyl linkage introduced to polymer backbone, the loose molecular packing with d-spacing of 27.7Å leads to moderate hole mobility. Furthermore, the high-lying HOMO level (-4.71eV) of PV2DTT results in poor air-stability under atmosphere. PTT2DTT exhibits dense d-spacing than PV2DTT because of more order crystalline domains, leading to a higher hole mobility. P2T2DTT shows the highest hole mobility up to 0.359 cm2V-1s-1 and the large Ion/off ratio of 7.1×106. It is consistent with the highly ordered edge-on lamellar polymer chain packing and fiber-like structure observed in XRD and AFM. The above results suggest that the biaxially extended 2DTT-based conjugated polymers could enhance the charge transport characteristics and emerge as a promising candidate for organic optoelectronic devices. 2. Synthesis, Optoelectronic Properties and Organic Field-Effect Transistors of Biaxially Extended Thieno[3,2-b]thiophene-Based Small-Molecules (Chapter 3): In this chapter, the optoelectronic difference between 2DTT-based small-molecules, the model compound of PT2DTT and PDTT2DTT have been investigated. Thiophene (T) and 2,2'-bithiophene (2T) were incorporated to biaxially extended 2DTT core via Stille-coupling and Suzuki reaction. The small-molecules show a good air stabilitydue to the HOMO level lower than -5.39eV while dramatic difference in the crystalline structure when extending the conjugation length were observed. Incorporating 2DTT with different length of thiophene has a dramatic influence not only in the surface structure and molecular packing but also in OFET performance. The high mobility of T-2DTT-T is attributed to the highly ordered lamellar structure and continuous interconnected large grain observed in XRD pattern and AFM image. The OFET characteristic of T-2DTT-T is comparable to the reported branched thiophene molecules, while the biaxially extended π-conjugation successfully enhance the air stability (HOMO= -5.57eV). 2T-2DTT-2T exhibits poor OFET performance mainly due to the short-range order and large grain boundaries which leads to the disturbing the conjugation of π-electrons and charge transfer. These above results indicate that 2DTT-based small-molecules can be efficiently tuned by introducing the different moieties into the core 2DTT.

參考文獻


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