| 摘要: | π共軛雜環化合物在有機電子材料中具有很大的開發價值，其中又以pentacene具有良好的光電性質並在有機薄膜電晶體 (OTFT)中具有高的載子移動率。然而，pentacene高的HOMO能階與狹窄的能隙，使其在空氣中容易被氧化，成為其致命缺點。相較於pentacene，併環噻吩於一般環境中具有良好的穩定性、光電性質以及較大的能隙;而具剛性及平面的π共軛系統，使之成為有效傳遞載子的核心，是一個有潛力的有機半導體材料。此外，併環噻吩分子間的硫與硫原子具有強烈的分子間作用力，使分子更緊密堆疊，進而提升載子移動率。
在我的研究中，利用Stille與Suzuki耦合反應，合成出以併環噻吩為核心的有機半導體材料，並將之應用於有機薄膜電晶體 (OTFT)、有機光伏打電池 (OPV)以及雙光子吸收 (2PA)。最後利用UV-vis、DPV與TGA來探討分子的光化學、電化學性質以及熱穩定性;製作成薄膜後以AFM、GIXRD以及GIWAXS探討其分子排列規則度與堆疊性。
開發出以三併環噻吩 (DTT) 與雙三併環噻吩 (BDTT) 作為中心主體，與苯基及全氟苯環作為末端基團，合成出不對稱小分子 FPP-DTT 及FPP-BDTT ，並將此系列材料養成單晶，製備成單晶及薄膜場效電晶體元件，經測試後具有P-type場效性質，單晶場效電晶體元件載子移動率分別為0.74 cm2V−1s−1 及 0.73 cm2V−1s−1 ，薄膜場效電晶體元件載子移動率為 0.15 cm2V−1s−1 及 0.20 cm2V−1s−1 。
以具硫醚碳鏈之聯噻吩作為末端基團以三併環噻吩作為核心主體，開發出可溶性有機小分子 BDTT-BST，經由溶液製程製成元件，具有P-type場效性質，載子移動率可高達1.7 cm2V−1s−1 。利用全氟苯環、噻吩作為末端基團，分別與多併環噻吩 TTA、DTT與TT之中心共軛單元耦合，開發出分子DFPT-TTA、DFPT-DTT、DFPT-TT，將一系列材料製程元件，具有N-type場效性質，其中分子DFPT-TTA、DFPT-TT載子移動率分別可達 0.43 cm2V−1s−1及0.33 cm2V−1s−1。
以四併環噻吩 (TTA) 作為核心主體，吡咯并吡咯二酮 (DPP) 為末端基團，合成出分子 DDP-TTAR，並將此分子運用於有機薄膜電晶體 (OTFT) 及有機光伏打電池 (OPV)中，其中場效電晶體元件電洞遷移率為 0.1 cm2V−1s−1，光電轉換效率為 4.02%。另外，分子Bis4T-DPP，運用於有機光伏打電池，與P3HT及PC71BM進行混摻製程元件，其光電轉換效率可達4.87%。將吡咯并吡咯二酮 (DPP)，於其兩端引入dicyanomethylene 基團，改變其分子整體之共振，開發出具有溶解度之N-type 醌型材料 DPPQ，經由溶液製程製成元件，其載子移動率可達 0.55 cm2V−1s−1。最後也將三併環噻吩 (DTT)運用於雙光子吸收 (2PA)，其中分子 Bis(4T)-DTT，經由測試下擁有雙光子激發截面值為3000GM，因此多併環噻吩也可作為發光基團，未來可運用於雙光子吸收應用上。
;Fused conjugated ring compounds attracted considerable interest in organic electronics. Among them pentacene based small molecules have been studied in organic electronics due to their excellent electronic and optical properties and owing to its high OTFT performance. The high mobility of pentacene is due to high order in the crystalline film. However, pentacene has the disadvantage of being easily undergo photo-oxidation in air due to its high lying HOMO and narrow band gap. Compared with pentacene, fused thiophene based conjugated small molecules are emerged as a potential organic semiconducting materials due to their excellent optoelectronic properties and relatively higher ambient stability originating from larger band gaps in the crystal structures, their rigid and flat -conjugated frameworks make them the most versatile and effective molecular scaffolds for organic functional materials. Additionally fused thiophenes possesses extensive molecular conjugation and strong intermolecular S•••S interactions promotes close molecular packing lead to higher charge carrier mobilities.
In my research, we have designed and synthesized fused thiophene based organic semiconductors using Stille and Suzuki cross-coupling reactions in various architectures for organic thin film transistors (OTFT), organic photovoltaics (OPV) and two photon absorption (2PA). Also, includes the comparative study of the optical, electrochemical and thermal properties of these organic semiconductors. OTFT, OPV and 2PA characterizations of these compounds suggested that fused thiophene based organic semiconductors are promising new class of organic materials for organic electronics. Electrochemical properties were investigated using differential pulse voltammetry, optical properties were examined by UV-visible absorption spectroscopy and thermal stability was observed through the thermogravimetric analysis (TGA) curves. Thin film microstructure and film morphology were examined by X-ray diffraction, atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXRD) and grazing incidence wide-angle X-ray scattering (GIWAXS) to understand the relationships between molecular structure, film morphology/crystallinity, and device performance. The molecular structures of organic semiconductors and their molecular packing properties were determined by single-crystal X-ray diffraction.
Asymmetric phenyl and perfluorophenyl end-functionalized dithienothiophene (DTT) and bisdithienothiophene (BDTT)-based fused-thiophene derivatives gave high p-channel mobilities of 0.74 and 0.73 cm2V-1s-1, respectively for single-crystal transistors and exhibited decent p-channel characteristics with a carrier mobility as high as 0.15 and 0.20 cm2/Vs respectively for organic thin-film transistor. Thio-alkyl (SR) substituted bithiophene (BST)-based semiconductors, end-capped with dithienothiophen-2-yl (DTT) group derivatives exhibits excellent p-type OFETs performance with mobilities up to 1.7 cm2 V-1 s-1 for organic field effect transistors (OFETs). Fused-thiophene (TTA, DTT, TT) semiconductors, end-capped with diperfluorophenylthien-2-yl (DFPT) groups (DFPT-TTA, DFPT-DTT, and DFPT-TT) are synthesized and characterized for organic thin-film transistors (OTFTs), DFPT-TTA and DFPT-TT exhibit good n-type TFT performance, with mobilities up to 0.43 cm2V−1s−1 and 0.33 cm2V−1s−1, respectively. Diketopyrrolopyrrole (DPP) and fused tetrathienoacene (TTA) frameworks are synthesized and characterized for OTFT and organic photovoltaics (OPV) exhibit hole mobilities approaching 0.1 cm2V-1s-1 and OPV efficiencies (PCE) > 4% for DDPP-TTAR. Organic photovoltaic cells based on Bis4T-DPP:P3HT:PC71BM blends achieve power conversion efficiencies (PCE) of 4.87%. Diketopyrrolopyrrole (DPP)-containing quinoidal small molecules for n-type organic semiconductors in thin film transistors (TFTs) exhibits maximum electron mobility up to 0.55 cm2V−1s−1 by solution process. Fused-thiophene-based chromophores are developed and characterized for a two-photon absorption (2PA) study exhibits the strongest and the most widely dispersed 2PA cross-section value of up to 3000 GM for DTT based chromophore. |
