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  • 學位論文

電子施體/受體共軛高分子:理論分析、合成、特性研究與元件應用

Donor-Acceptor Conjugated Polymers:Theoretical Analysis, Synthesis, Characterization, and Device Application

指導教授 : 陳文章

摘要


電子施體/受體共軛高分子由於其在發光二極體、光伏打電池與薄膜電晶體上廣泛應用而備受囑目。在此藉由結合理論與實驗探討一系列不同電子施體/受體高分子結構。此博士論文目標在於分子設計及合成新穎高分子材料,說明調控電子及光電性質之結構和性質關係,及製備元件應用於電晶體和化學感測器上。 本文的第一個部分(第二章)針對不同聚甲亞胺共軛高分子之幾何結構與電子特性進行理論分析。基態聚甲亞胺之分子結結構與電子特性可由密度泛函理論來做計算。理論研究中發現PPV和PAZ具有共平面結構,然而PPI卻是非共平面的結構且PPI電子組態介於PPV和PAZ之間。若苯環被五元雜環系列取代,如3,4-二氧乙基噻吩、吡咯、噻吩、砆喃、噻二唑等,其非共平面之結構可變為更為共平面之結構。由於其共平面結構及電子施體/受體分子內電荷轉移,使PEEI、PYYI、PFFI和PTTI 理論能隙約在1.11至1.67eV之間。由於PThThI有較大鍵長差及缺乏電荷傳遞特性,使其相較於其他分子有較大的能隙 (2.47eV)。除PThThI 外,五元雜環聚甲亞胺價帶帶隙約為562-613 meV之間,遠大於PPI (247 meV)及PPV (373 meV)。由理論分析之結果可知聚甲亞胺之電子特性可藉由不同環幾何結構進行調控。在此所提出新穎共平面聚甲亞胺材料將在透明導體及薄膜電晶體上有極大潛力。 本文的第二個部分(第三章)利用2,7-雙甲醛基-9,9’-雙辛基芴及二胺合成可溶性的聚甲亞胺(PFI及PFCI)。而由咔唑取代芴會有扭結紊亂排列,造成離子能降低但會提昇能隙帶。然而PFI及PFCI吸收及放光光譜易受良好溶劑/非良好溶劑比例、酸環境或金屬離子影響,這些光譜調控改變可由高分子結構平面性和分子間電荷轉移來解釋。由密度泛函理論計算出PFI及PFCI因環上相鄰氫原子間斥力導致非共平面結構,可藉由塞吩(PFTI)及3,4-二氧乙基塞吩(PFEI)五元雜環來改進。此類聚甲亞胺擁有共平面結構及分子內電荷傳遞使PFTI及PFEI的能隙分別為2.17及2.03 eV,且其較小電子等效質量,使此高分子有半導體特性並可應用於有機光電元件。 本文的第三個部分(第四章)為開發新穎雙十烷氧基苯為主體電子施體/受體交替共軛高分子材料,由零價鉑催化劑之鈴木偶合共聚法所合成。所研究之電子受體包括噻嗯並[3,4-b]-吡嗪(TP)、2,1,3-苯並硫二唑(BT)、喹喔啉(Q)及吡啶(Py)等,可用來和苯環(P)做比較。所合成出之四種電子施體/受體高分子於常見有機溶劑具有良好的溶解性及熱穩定性,其光學吸收峰於甲苯中約在349至605 nm左右,薄膜狀態約在375至678 nm左右,較POC10-P皆有顯著紅移現象。POC10-TP於此系列材料中為最低能隙高分子,表示具有較強分子內電荷傳遞。由電化學循環伏安法可得LUMO和HOMO分別約在-3.38至-3.10 eV及-5.45至-4.65 eV之間。POC10-TP由於其電洞傳遞遷移率1.1 × 10-3 cm2/VS,電流開關比為60可作為主動半體體材料,其較廣吸收峰及高遷移率可應用在軟性太陽能材料開發。

並列摘要


Donor-Acceptor conjugated polymers are of wide interests for electronic and optoelectronic devices, such as light-emitting diode, photovoltaic cells and thin film field effect transistors. However, systematic studies on the synthesis and electronic and optoelectronic properties of such polymers have not been fully explored yet. The goals of this thesis include the following issues: (1) molecular design and synthesize new conjugated polymers, (2) elucidate the structure-property relationship that dominate the electronic and optoelectronic properties, and (3) the application of the synthesized donor-acceptor conjugated polymers on thin film transistor and chemical sensors. In the first part of this thesis (Chapter 2), theoretical analysis on the geometries and electronic properties of various conjugated poly(azomethine)s is reported. The theoretical ground-state geometry and electronic structure of the studied poly(azomethine)s are optimized by the hybrid density functional theory (DFT) method treated in periodic boundary conditions at the B3LYP level of theory with 6-31G basis set. The geometry and electronic structure of poly(1,4-phenylenemethylidyneitrilo-1,4-phenylene-nitrilomethylidyne) (PPI) are compared with those of poly(p-phenylene vinylene) (PPV) or polyazine (PAZ). The theoretical results suggest the non-coplanar conformation of PPI but PPV and PAZ with a coplanar conformation. The electronic properties of PPI are in the intermediate between PPV and PAZ. The non-coplanar conformation of PPI could be released if the phenylene ring is replaced by the five-member ring of 3,4-ethylenedioxythiophene (PEEI), pyrrole (PYYI), thiophene (PTTI), furan (PFFI), or thiadiazole (PThThI). The theoretical band gaps of PEEI, PYYI, PFFI, and PTTI are in the range of 1.11~1.67 eV, which is due to the coplanar configuration or donor-acceptor intrachain charge transfer. However, the large bond length alternation or lack of charge transfer characteristic makes the PThThI with a larger Eg of 2.47 eV than others. The trend on the IP or EA of the studied conjugated poly(azomethine)s are consistent with the electronic characteristic of the aromatic ring. The upper valence bandwidth of the studied five-member ring based poly(azomethine)s except PThThI is in the range of 562-613 meV, which is larger than that of PPI (247 meV) or PPV (373 meV). The results suggest that the electronic properties of conjugated poly(azomethine)s could be varied through various ring structures. The proposed new coplanar conjugated poly(zomethine)s can be potentially used as transparent conductors or thin film transistors. In the second part of this thesis (Chapter 3), soluble conjugated poly(azomethine)s, PFI and PFCI, were synthesized from 2,7-diformyl-9,9’-dioctylfluorene (DFOF) with diamines. The replacement of the fluorene (PFI) by carbazole (PFCI) reduces the ionization potential but enhances the band gap (Eg) due to the kink disorder introduced by the 3,6-carbazole. The optical absorption or photoluminescence of the synthesized PFI or PFCI is sensitive to good /poor solvent ratio, acid environment, or metal ions. The variation of the planarity on the polymer backbone and intermolecular charge transfer explain the above spectral tuning by chemical species. The theoretical results based on the density functional theory (DFT) suggest that the PFI and PFCI show a non-coplanar conformation due to steric repulsion force between the adjacent hydrogen atoms. It could be resolved by replacing the fluorene or carbazole ring by thiophene (PFTI) or 3,4-ethylenedioxythiophene (PFEI). The coplanar geometry and possible intramolecular charge transfer leads to the band gap of 2.17 and 2.03 eV for the PFTI and PFEI, respectively. The smaller effective mass of the PFTI or PFEI also indicates both polymers could be p-type semiconductors for organic electronics. In the third part of this thesis (Chapter 4), novel didecyloxyphenylene (POC10) based donor-acceptor alternating conjugated polymers were synthesized by palladium(0)-catalyzed Suzuki coupling polycondensation. The studied acceptors include thieno[3,4-b]-pyrazine (TP), 2,1,3-benzothiodiazole (BT), quinoxaline (Q) and pyridine (Py) which could be used to compare with the parent phenylene (P). The synthesized polymers possessed good solubility in common organic solvent and high thermal stability. The optical absorbance peak of these four donor-acceptor polymers appears in the range of 349-605 nm in toluene and 375-678 nm in solid state, respectively, which show a significant red-shift than that of POC10-P. The POC10-TP exhibits the smallest band gap (1.47 eV) among the studied polymers, indicating a strong intramolecular charge transfer. The prepared polymers also emitt intense blue, olivine or featureless broad bands, depending on the acceptor moiety. Cyclic voltammetry reveals that the polymers are susceptible to both electrochemical oxidation and reduction with a LUMO level ranging from -3.38 to -3.10 eV and a HOMO level ranging from -5.45 to -4.65 eV. The hole mobility and current on/off ratio of POC10-TP as the active semiconducting materials in thin film transistors are 1.1 × 10-3 cm2/VS and 60 at ambient atmosphere, respectively. The combined broad absorption and moderately high mobility make POC10-TP promising for plastic solar cell applications.

參考文獻


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