含界面連接劑之聚己烷基噻吩/二氧化鈦層狀結構材料之合成及其光激特性之探討

Syntheses and Photo-induced Properties of Novel Poly(3-hexylthiophene)/TiO2 Layer Structure Containing Interface Linker

劉惠如(Huei-Ru Liou)

指導教授 ： 王立義

國立臺灣大學/工學院/高分子科學與工程學研究所/碩士(2005年)

https://doi.org/10.6342/NTU.2005.02700

摘要

在有機太陽能電池的材料中， 增加有機及無機材料間的接觸面積, 進而提升元件的工作效率, 是一個相當有趣且主要的研究方向; 然而, 由於有機材料以及無機材料本身性質上的差異, 造成彼此在混掺時, 常有相分離的現象產生。 因此, 在本研究中, 我們製備出一系列的Donor-Acceptor (D-A) linkers, 將其應用在簡單的poly(3-hexylthiophene)/TiO2層狀結構中,進而形成poly(3-hexylthiophene)/D-A linker/TiO2 的新型架構; 該系列D-A linkers之分子結構包含三個主要的部份: phosphonic acid, 長烷鏈, 以及噻吩環。其中的phosphonic acid可用與TiO2形成穩定的鍵結; 而噻吩環則提供為電化學聚合的起始單元,進而將不相容的TiO2及poly(3-hexylthiophene), 藉由D-A linkers的連接來降低異相分離及空洞的產生; 此外, 由不同長度的長烷鏈來調整D-A介面間的距離, 進一步探討長烷鏈的長度對於形成分子自組裝膜的堆疊情形, 以及對於後續的電化學聚合反應之影響。

在本研究中,我們利用所合成出三種D-A linkers, 分別為2-thienyl phosphonic acid (TPA), 6-(2-thienyl)hexyl phosphonic acid (THPA), 以及10-(2-thienyl)decyl phosphonic acid (TDPA), 分別自組裝於燒結過後的TiO2膜材表面, 然後藉由接觸角量測得知浸泡時間與接觸角的關係,結果顯示三組樣品的表面吸附分別在八小時後呈飽和。 經由化學分析能譜儀鑑定, 顯示自組裝單層膜皆在TiO2表面有phosphonic acid以及噻吩的訊號, 直接說明了D-A linkers在TiO2表面的存在; 且由原子力顯微鏡的觀察, 得知在接上D-A linker的自組裝單層膜與未進行自組裝的TiO2的表面型態沒有太大的差異.

在電化學聚合中,我們利用定電壓的方式, 分別以D-A linkers的自組裝單層膜及TiO2作為工作電極來聚合poly(3-hexylthiophene) (P3HT), poly(3-methylthiophene) (P3MT)以及poly(2,2’-bithiophene) (PBT), 然而發現P3HT及P3MT皆無法聚合在THPA和TDPA的自組裝單層膜, 而PBT則是無法聚合在TDPA的自組裝單層膜, 可能是由於D-A linker結構中的長烷鏈在工作電極上形成電阻, 阻礙高分子在D-A linker自組裝單層膜上的成長; 由原子力顯微鏡結果得知P3HT/D-A linker/TiO2 層狀材料中P3HT的表面型態相較於P3MT及PBT均來得平整； 且由紫外光-可見光譜儀和螢光光譜儀觀察, 發現加入D-A linkers後, 雖然在膠體層析法中測出的分子量不同, 然而對於材料整體的最大吸收, 共軛長度以及螢光放光位置皆沒有影響。

關鍵字

界面連接劑 ； 聚己烷基噻吩

並列摘要

In organic solar cell, many efforts have been devoted to increase the interfacial area between donor and acceptor, and thus increase the power efficiency of the device. However, the voids or the phase separation between heterogeneous phases are also a factor which may result in low cell efficiency. In our research, we developed a series of D-A linkers which were applied into layer structure, poly (3-hexylthiophene)/D-A linker/TiO2. The D-A linkers are composed of three parts including phosphonic acid, alkyl chain, and thiophene ring. Poly (3-hexylthiophene) could thus link to TiO2 by introducing D-A linkers whose phosphonic acid anchored to TiO2, and thiophene ring initialized electrochemical polymerization of 3-hexylthiophene. Therefore, the voids and phase separation between heterogeneous phases may be reduced. The interfacial distance between donor and acceptor can be controlled by introducing alkyl spacers with different length that may cause different packing behaviors or different conditions of electrochemical polymerization.

In this study, the D-A linkers, 2-thienyl phosphonic acid (TPA), 6-(2-thienyl)hexyl phosphonic acid (THPA), and 10-(2-thienyl)decyl phosphonic acid (TDPA) were self-assembled to TiO2 in ethanol solution containing D-A linkers. The contact angle measurements indicate the adsorptions onto TiO2 to reach saturation are around 8 hours for all D-A linkers. AFM images indicate the surface morphology of the self-assembled monolayer (SAM) is similar to that of TiO2 only. Besides, the direct evidence of the existence of D-A linkers on the TiO2 surface was obtained from the ESCA spectra of D-A linkers modified TiO2 substrates .

Electrochemical polymerization was carried out by the potential-static method using D-A linkers modified TiO2 or TiO2 only substrates as working electrodes. However, the electrochemical polymerization of poly(3-hexylthiophene) (P3HT) and poly(3-methylthiophene) (P3MT) did not proceed in THPA- and TDPA- modified TiO2 substrates, and the electrochemical polymerization of poly(2,2’-bithiophene) (PBT) did not proceed in TDPA-modified TiO2 substrates. These phenomena may be caused by the resistance of the insulting alkyl spacers of D-A linkers. From the AFM images of polymers on D-A linkers modified TiO2, P3HT showed a smoother surface than P3MT or PBT. GPC was employed to examine the molecular weight of the electrochemically polymerized P3HT on TiO2 only and TPA-modified TiO2. Because of the barrier caused by the D-A linker, the molecular weight of P3HT on TiO2 is larger than that on TPA-modified TiO2. However, the conjugation length didn’t change with the molecular weight of polymer from UV-vis measurements, and the positions of maximum emissions of polymers on D-A linker modified TiO2 or TiO2 only substrates were the same by PL measurements.

並列關鍵字

Interface linker ； electrochemical polymerization

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