新穎雙軸延伸噻吩-異靛藍素電子施體-受體共軛高分子於有機光電元件應用

Synthesis of Novel Donor-Acceptor Conjugated Polymers Based on Biaxially Extended Thiophene and Isoindigo for Optoelectronic Device Applications

洪千雯(Chian-Wen Hong)

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(2016年)

https://doi.org/10.6342/NTU201610178

摘要

有機共軛高分子材料近年來因其低廉製程、可伸縮撓曲特性及可大面積製造等優點廣泛應用於有機場效電晶體、光伏打電池等電子元件中。新穎光電高分子材料的發展中，發現改變高分子的側鏈結構，可有效調控其溶解度、鏈間的排列及薄膜型態；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、吸收光譜範圍及水氧穩定性。本碩士論文研究目標在於開發一系列以異靛藍素為主體並具有雙軸延伸結構之電子施體-受體共軛高分子材料，並探討其結構設計對於高分子薄膜形態與光電特性之影響，系統性的探討高分子結構對於載子遷移率與太陽能電池效率之影響。
本文的第一部分(第二章)-新穎異靛藍素電子施體/受體共軛高分子之合成及特性鑑定-合成一系列以異靛藍素為主體並具有雙軸延伸結構之共軛高分子材料，包含PIITT4T、PIITT4TSi、PII2T4T、PII2T4TSi、PII2T8T與PII2T8TSi，藉由導入不同雙軸延伸之噻吩單體(TT4T、2T4T及2T8T)與側鏈之異靛藍素基團利用Stille coupling 進行微波聚合，進而探討其高分子材料之熱性質、光電性質與型態分析。此系列之高分子能隙在1.59 eV到 1.63 eV之間，因其利用雙軸的方式延伸共軛長度及導入異靛藍素之電子受體，其中，PII2T8T (-5.38 eV) 與PII2T8TSi (-5.32 eV) 展現較低的最高佔有分子軌域能階，主因為2T8T基團具有側鏈分支的結構使扭轉程度較大。
本文的第二部分(第三章)-新穎異靛藍素電子施體/受體共軛高分子於場效電晶體及光伏打電池之應用-延續第二章，將其合成之一系列新穎異靛藍素電子施體/受體的共軛高分子應用於場效電晶體及光伏打電池。其中，PII2T4TSi具有最高之場效電晶體電洞遷移率為0.53 cm2V-1s-1 ，因其雙軸延伸共軛單元 (2T4T) 較具平面性及異靛藍素含矽氧烷末端基團可使分子排列較為緊密，提升結晶性。此外，對於共軛高分子混摻碳七十衍生物做為光伏打電池主動層材料，PIITT4T展現出最好的光電轉換效率可達1.88 %。
整體研究成功合成一系列新穎異靛藍素電子施體/受體並具有雙軸延伸結構之共軛高分子材料應用於場效電晶體及光伏打電池，其材料有不錯的電洞載子傳輸能力及太陽能光電轉換效率，在光電元件的應用上是具有發展性的。

關鍵字

異靛藍素 ； 共軛高分子 ； 雙軸延伸側鏈 ； 場效電晶體 ； 光伏打電池

並列摘要

Organic conjugated polymer is considered as one of the most appropriate candidates for electronic and optoelectronic applications owing to its potential advantages, including low cost, light-weight, good solution-processability, and flexibility, over inorganic or organic small-molecular counterparts. In the recent progress of polymer community, side chains are act as a crucial component in the design of novel conjugated polymers. They not only directly relate to the solubility but also affect the molecular packing motifs and thin film morphologies. The goal of this thesis is to address the effect of conjugated or alkyl side chain structures on the polymer thin film morphologies and the optoelectronic properties. In addition, the field-effect mobilities and photovoltaic characteristics are also probed to explore the structure-property relationship through side chain engineering design systematically. The details of explorations are summarized as below:

1. Synthesis and Characterization of Novel Donor-Acceptor Conjugated Polymers Based on Biaxially Extended Thiophene and Isoindigo (Chapter 2): a series of novel isoindigo-based conjugated polymers, including PIITT4T, PIITT4TSi, PII2T4T, PII2T4TSi, PII2T8T, and PII2T8TSi, have been synthesized via Stille coupling polymerization enable various biaxially extended donor moieties (TT4T, 2T4T, and 2T8T) and isoindigo acceptor with different side chain. Tunable polymer structural, optical, and electrochemical properties were observed because different π-conjugated building blocks in the polymer main chain and side chain, affecting the conformation of polymer backbone. The studied polymers have the optical band gaps between 1.59 and 1.63 eV, owing to biaxially extended donor moieties and isoindigo acceptor groups. PII2T8T (-5.38 eV) and PII2T8TSi (-5.32 eV) exhibited lower HOMO levels than other studied polymers, which was mainly due to the conformational distortion of the 2T8T moiety on polymer chains. Owing to the octyldodecyl group of the isoindigo moiety with a severe backbone twisting, the HOMO levels of PIITT4T, PII2T4T, and PII2T8T were deeper than PIITT4TSi, PII2T4TSi, and PII2T8TSi, respectively. Details of polymer morphologies were investigated using atomic force microscopy (AFM) and grazing incidence X-ray diffraction (GIXD) systematically. PII2T4TSi exhibited a smaller π-π stacking distance (3.56 Å) than other studied polymers, and had both face-on and edge-on packing structures in thin films.

2. Novel Donor-Acceptor Conjugated Polymers Based on Biaxially Extended Thiophene and Isoindigo for Field-Effect Transistors and Photovoltaic Cells (Chapter 3): Top-contact field-effect transistors (FETs) were used to explore the charge carrier transport ability of the studied polymer films. Among the isoindigo-based polymers, PII2T4TSi exhibited the highest hole mobility (0.53 cm2V-1s-1) using o-DCB as processing solvent, with on/off current ratio around 105. In addition, the power conversion efficiencies (PCEs) of the photovoltaic cells based on polymer/PCBM blends were in the range of 0.69–1.88 % for our synthesized polymers. Among them, PIITT4T-based device could achieve the best PCE of 1.88 % using o-dichlorobenzene as processing solvent. The above results demonstrated that the new-designed polymers could serve as a promising candidate for polymer optoelectronic device applications.

並列關鍵字

Isoindigo ； conjugated polymers ； biaxially extended side chain ； field-effect transistors ； photovoltaic cells

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