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標題: | 新穎共軛高分子半導體及其側鏈結構探討與有機光電元件應用 Designing Conjugated Polymers through Modification of Side Chains and Application in Optoelectronic Devices |
作者: | Chien Lu 呂謙 |
指導教授: | 陳文章(Wen-Chang Chen) |
關鍵字: | 側鏈結構,共軛高分子半導體,分子堆疊,可拉伸電子元件,太陽能電池, side chain engineering,conjugated polymers,molecular packing,stretchable electronics,organic photovoltaics, |
出版年 : | 2016 |
學位: | 博士 |
摘要: | 新穎半導體共軛材料因其在有機電子元件,如場效應電晶體、有機太陽能電池與有機記憶體元件之應用性以及其低成本與溶液操作性等優勢受到研究者矚目,在共軛高分子材料發展中,側鏈結構之設計可以調控高分子多向排列結構以及薄膜型態。本論文目標在於開發具備不同共軛側鏈或烷基側鏈修飾於施體受體共軛材料,並探討其光電性質與元件特性,依不同材料結構與應用主要可分為以下三類:
1. 合成二維分支噻吩側鏈共軛高分子於場效應電晶體與有機太陽能電池應用:本論文第二章中開發一系列具二維分支噻吩側鏈(4T)之半導體高分子(P4T2T, P4T2Se, P4TTT, and P4TDTT)並探討其化學結構與光電性質的 關係。與4T共聚共軛基團(2T, 2Se, TT, and DTT)之大小與對稱性可改變共聚之高分子主鏈結構之平面性與分子堆疊結構,依此特性可於P4TDTT高分子得到最佳化載子遷移率0.610 cm2V-1s-1並具有優異的環境穩定性。本論文第三章中將延續探討二維分支噻吩側鏈(4T)之半導體高分子平面性之結果,開發具二維分支噻吩側鏈(4T)和二維延伸分支側鏈噻吩側鏈(8T)之半導體高分子(P4TV與P8TV),其最佳化載子遷移率分別為0.12與0.0018 cm2V-1s-1,同時其最佳高分子/PC71BM異質接面太陽能電池之光電轉換效率分別為4.04與2.69%。P4TV因期限性側鏈結構具有較優異之結晶性與電荷傳輸能力,而P8TV則因其分支側鏈結構有效降低最高佔據分子軌道而具有優異之環境穩定性。 2.含二維分支噻吩側鏈共軛高分子基團之施體受體共軛高分子:本論文第四章探討具有不同受體強度之施體受體共軛高分子(P4T-DTT, P4T-Q, P4T-BT, P4T-DPP, PDTT-DPP)其化學結構與不嵌入電荷儲存層之電晶體式記憶體特性之關聯。受體基團之電子親和力越強共軛高分子半導體之電荷儲存能力越強,P4TDPP與PDTT-DPP高分子可展現高達80V與60V之電荷儲存窗口與30000秒以上之儲存時間,並表現出多級記憶之快閃記憶體特性。為了近一步探討二維分支噻吩側鏈半導體高分子於施體受體結構中之光電特性,本論文中第五章開發具Isoindigo (IIG) 和其衍生物Thienoisoindigo (TIIG)之二維分支噻吩側鏈半導體高分子(PBDT-IIG、PBDT-TIIG),討論其受體分子之共平面性與受體強度對共軛高分子之光電性質與結晶影響,並系統性的研究此類雜芳烴衍生物受表面改質影響之薄膜表面結構於場效應電晶體和有機異質接面太陽能電池之應用,其最佳化載子遷移率分別為0.103與0.071 cm2V-1s-1,同時其最佳高分子/PC71BM異質接面太陽能電池之光電轉換效率分別為5.86與2.55%。 3.分支烷基側鏈於半截經共軛高分子之機械性質與可拉伸性之影響: 近年來,高分子之可撓性與拉伸性被廣泛應用於各類材料上,而具有可撓性與拉伸性之有機電子元件更是未來軟性元件趨勢之一。本論文中第六章主要探討拒辦結晶特性之poly(tetrathienoacene-diketopyrrolopyrrole)之高分子與其不同烷基側鏈衍生物在薄膜狀態下之拉伸特性與斷裂行為,並進一步量測此高分子薄膜於拉伸狀態下之表面結構與電荷傳輸特性變化。其中具分支烷基側鏈之半導體高分子可承受40%之應變而不產生斷裂,並在拉伸至100%之應變時仍可保持其載子遷移率在0.1 cm2V-1s-1,在進一步的分子結晶堆疊結構中可發現,此系列分支烷基側鏈高分子中具edge-on排列特性之高分子較具有edge-on與face-on混和排列結構之高分子可展現出更優異之機械性質與電荷傳輸特性,由於face-on排列之高分子烷基側鏈堆疊方向與拉伸方向平行,而烷基側鏈堆疊相較於主鏈π-π堆疊較弱更亦受應力而變形,使其於拉伸下之薄膜連續性較差,此研究提出設計新穎具有高載子遷移率軟性共軛高分子之概念。 從以上三類材料開發策略中,可成功利用側鏈結構設計並調整共軛高分子半導體之光電特性載子傳輸率太陽能光電轉換效率非揮發性記憶特性與機械性質,充分表現出此類共軛高分子半導體於未來有機電子元件之應用潛力。 The development of novel organic conjugated materials has gained momentum in recent times due to their possible applications in organic photovoltaic (OPV), organic field-effect transistor (OFET) devices, and organic memory devices where their lower cost, light weight, and mechanical flexibility are all attractive properties. The exploration of the structure property relationships of π-conjugated systems provide an important insight for high-mobility, ambient stable, and solution-processable semiconducting polymers. The goal of this thesis is to address the effect of molecule design including side chain engineering and donor-acceptor structure on the optoelectronic properties and electrical characteristics of the conjugated polymers, as shown in following approaches: 1. Synthesis of two-dimensional thiophene-extended conjugated polymers for OFET and OPV application In chapter 2, the synthesis, morphology, and field-effect transistor characteristics of biaxially extended thiophene-based conjugated copolymers, P4T2T, P4T2Se , P4TTT, and P4TDTT consisting of bithiophene, biselenophene, thieno[3,2-b]thiophene, dithieno[3,2-b:2’,3’-d]thiophene, respectively. The effect of inserted moieties and symmetry on the polymer backbone and their corresponding molecular packing was explored. P4TDTT exhibited a smaller d-spacing and π-π stacking distance due to enhanced interchain interaction and denser molecular packing, showing the highest hole mobility up to 0.610 cm2V-1s-1. Two-dimensional extended 4T- and octithiophene (8T)-vinylene conjugated polymers, P4TV and P8TV were investigated in chapter 3. P4TV and P8TV exhibited smaller energy band gaps of 1.69 and 1.78 eV than that of parent polythiophenes, respectively, due to the reduced conformational backbone distortion by the vinylene linkage. The highest field effect hole mobilities of P4TV and P8TV were 0.12 and 0.0018 cm2V-1s-1, respectively, which could be related to the ordered structure of P4TV. The power conversion efficiency (PCE) of the P4TV/ PC71BM and P8TV/ PC71BM based photovoltaic cells (PV) was 4.04 % and 2.69 %, respectively. However, P8TV had a better environmental stability attributed to its lower-lying HOMO energy level. 2. Biaxially thiophene-extended thiophene-based donor-acceptor copolymers With the knowledge about biaxially extended thiophene-based polymers, the effects of donor-acceptor chemical structures on the memory characteristics were investigated in chapter 4. The charge storage capability of transistor-type memory devices was found to be related to the electron affinity of the used donor-acceptor copolymers. The 4T-based D-A copolymers with the strong electron-accepting benzothidiazole and diketopyrrolopyrrole exhibited large memory windows (55 and 79 V, respectively). The 4T-based donor-only copolymer and 4T-based D-A copolymer with a weak electron-withdrawing qunioxaline showed smaller memory windows of 7 and 11 V, respectively. This indicates that the strong acceptors may enhance memory behaviors. In addition, the conformational torsion in polymer backbone also enhanced the charge storage ability. The ON and OFF states of the D-A polymer devices can be maintained over 3×104 s with the Ion/Ioff current ratios of 102-105, and the write-read-erase-read (WRER) cycles can be operated over 200 cycles, indicating excellent nonvolatile flash-type memory behaviors. In chapter 5, systematic study on the effects of heteroarenes on the solid state structure and optoelectronic properties of isoindigo analogues, namely PBDT-IIG and PBDT-TIIG, where BDT buliding block also contains thiophene side chains, were explored as the donor(D)-acceptor(A) copolymers. The optical absorption, frontier orbitals, backbone coplanarity, molecular orientation, solubility, film morphology, charge carrier mobility, and solar cell performance are critically influenced by the heteroarenes in the acceptor subunits. PBDT-IIG exhibits good p-type OFET performance with hole mobility up to 1.03 × 10-1 cm2V-1s-1, whereas PBDT-TIIG displays ambipolar mobilities of μh = 7.06 × 10-2 cm2V-1s-1 and μe = 2.81 × 10-4 cm2V-1s-1. PBDT-IIG and PBDT-TIIG blended with PC71BM yield promising power conversion efficiencies (PCEs) of 5.86% and 2.55% , respectively. The differnt electrical transport characteristics could be attributable to the differnt packing orientations of the two polymers.Although PBDT-TIIG could preserve a long-range face-on packing alignment to meliorate its photocurrent in OPV applicaitons, the low open-circuit voltage caused by its high-lying HOMO energy level and greater recombination demonstrates the trade-off between light absorption and solar cell performance. Nevertheless, PBDT-TIIG with a PCE of 2.55% is the highest reported PCE to date for the TIIG-based systems. 3. The mechanical and conformational properties of semi-crystalline conjugated polymers with alkyl side chain engineering The design of polymer semiconductors possessing high charge transport performance, coupled with good ductility, remains a challenge. Understanding both the distribution and behavior of crystalline domains and amorphous regions in conjugated polymer films, upon an applied stress, should provide general guiding principles to design stretchable organic semiconductors. In chapter 6, structure-property relationships (especially in both side chain and backbone engineering) were investigated for a series of poly(tetrathienoacene-diketopyrrolopyrrole) (PTDPPTFT4) polymers. PTDPPTFT4 incorporated with branched side chains and additional thiophene spacer in the backbone was found to exhibit the best mechanical endurance and, in addition, does not show crack propagation until 40% strain. Furthermore, this polymer exhibited a hole mobility of 0.1 cm2V-1s-1 even at 100% strain, or after recovered from strain, which reveals a prominent continuity and viscoelasticity of the polymer thin film. The molecular packing orientations (either edge-on or face-on) of the studied polymers significantly was also found to affect the mechanical compliance of the polymer films. The improved mechanical property of the polymers was attributed to both the elasticity from the polymer’s amorphous regions and the intrinsic packing arrangement of its crystalline domains. From these approaches, we successfully designed and tuned the optoelectronic properties, charge mobility, power conversion efficiency, memory volatility, and mechanical ductility of semiconducting polymers in different organic electronic devices. These results showed the potential significance of these semiconducting polymers in the application of future organic electronics. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/51562 |
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