Thieno[3,2-b]thiophene-based Semiconducting Materials with Biaxially Extended Side Chains: Synthesis, Morphology and Organic Field-Effect Transistor Applications
Date Issued
2014
Date
2014
Author(s)
Chao, Pei-Yin
Abstract
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.
Subjects
雙軸延伸共軛系統
共軛小分子
共軛高分子
噻吩並噻吩
有機場效電晶體
Type
thesis
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