- 學位論文
聚己基塞分/2-(烷基磷酸)塞分/二氧化鈦層狀異質界面之製備及性質研究
Fabrications and Properties of Poly(3-hexylthiophene) / w-(2-Thienyl) Alkylphosphonic Acids / Titania Layer Heterojunction
摘要
有機太陽能電池材料的異質界面，能利用兩種異質材料電子親和性的不同，幫助光激發產生的exciton電荷分離，產生電流。但是有機與無機材料彼此間的相容性不佳，可能會導致接合界面間產生空洞，而阻礙電子的傳遞。所以我們設計了一個新型的層狀異質界面，使有機的poly(3-hexylthiophene)與無機的TiO2藉著donor-acceptor (D-A) linkers形成共價性的鍵結，而彼此緊密的接合。 在本研究中，此一系列的D-A linkers之分子結構包含三個主要的部分：磷酸官能基、長烷鏈、以及塞分環。其中的磷酸官能基可用與TiO2形成穩定的鍵結，而塞分環則提供為電化學聚合的起始單元；另外我們可由不同長度的長烷鏈來調整D-A界面間的距離，並進一步探討長烷鏈的長度對於後續的電化學聚合反應之影響。 我們首先利用核磁共振光譜儀來鑑定三種合成出來之D-A linkers的化學結構，在linkers吸附到TiO2表面形成自組裝單層膜之後，我們利用接觸角的量測得知浸泡時間與接觸角變化的關係，結果顯示三組樣品的表面吸附分別在一小時後即呈飽和的狀態。另外我們分別利用X射線光電子能譜來鑑定linkers之磷酸官能基與TiO2表面之鍵結；熱重分析法(TGA)與UV檢量線的測定來鑑定linkers在TiO2表面的含量；並由原子力顯微鏡的觀察，得知在接上D-A linkers的自組裝單層膜與未進行自組裝的TiO2表面型態沒有太大的差異。 在電化學聚合中，我們採用定電流的方式，並由測時電位(chronopotentiogram)的分析得知越長的alkyl chain在工作電極上形成越大的電阻，並由凝膠滲透層析儀(GPC)測出的分子量證實，其alkyl chain形成的電阻會阻礙高分子在自組裝單層膜上的成長；但由原子力顯微鏡的觀察，異質界面層狀材料中，P3HT的表面型態並不會有太大的差異；且由紫外光-可見光譜儀和螢光光譜儀的觀察，發現不同alkyl chain長度的D-A linkers，雖然其聚合之P3HT在凝膠滲透層析儀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；但由量子效率的量測，我們卻發現經由自組裝單層膜成長的P3HT薄膜有較高的quenching efficiency，且alkyl chain長度越短，效率越高，此一現象可能是因為D-A linkers能以共價鍵結將二氧化鈦和共軛高分子連接起來，避免了空洞的產生，而使光照射後產生之電子與電洞得以迅速的分離，讓能量傳遞效率大為提高所致。
並列摘要
The heterojunction of organic solar cell is combined by two semiconductor materials which have different energy band gap. We can use the different electron affinities of these two materials to favor exciton separation, then to generate current. However, the incompatibility between organic and inorganic materials would cause voids in the face of the heterojunction. And it will block the electron transfer. So we developed a series of donor-accepter linkers which were applied into layer structure. The using of D-A Linkers has led to the synthesis of covalently linked donor-acceptor system. In our research, the D-A linker structure consists of three major parts : phosphonic acid, alkyl chain and thiophene ring. Poly (3-hexylthiophene) could thus link to TiO2 by introducing D-A linkers whose phosephonic acid anchored to TiO2, and thiophene ring initialized electrochemical polymerization of 3-hexylthiophene. The interfacial distance between donor and acceptor can be controlled by introducing alkyl spacers with different length that may cause different conditions of electrochemical polymerization. First, we use NMR spectrum to characterize the chemical structures of three different D-A linkers. After the linkers form the self-assembled monolayers on TiO2, we can measure the contact angle to realize the relationship with immersing time. And it indicated the adsorptions onto TiO2 to reach saturation are around one hour for all D-A linkers. Besides, the analysis of XPS spectra identified the bonding structure of all D-A linkers on TiO2 particles. And the use of TGA and UV-vis spectra calculated the content of linkers on the TiO2 particles. AFM images indicate the surface morphology of the self-assembled monolayers is similar to that of TiO2. In the electrochemical polymerization process, by the chronopotential method, the chronopotentiogram analysis showed the longer alkyl chain brings the bigger resistance. Also, the molecular weight measuring by GPC proved that the resistance resulting from alkyl chain blocked the polymerization on the self-assembled monolayers. However, from the AFM images of polymers, weather alkyl chain or resistance exist or not, it has no influence on the surface morphology of P3HT. Though the measurement from UV-vis and PL, although the different alkyl chain length caused the different molecular weight of P3HT, it didn’t affect the maximum of absorption wavelength and the emissions positions. We found out the P3HT propagating from linker-modified TiO2 substrates have higher quenching efficiency though the measurement of quantum yield. And the shorter length the alkyl chain is, the higher efficiency it results. As we believed, D-A linkers covalently linked TiO2 and conjugated polymers. This phenomenon avoided the generation of pin holes, and raised the considerable efficiency of the electron transfer between donor and acceptor.
參考文獻
延伸閱讀
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