含介面連接劑之聚己烷基噻吩/二氧化鈦奈米複合材料之合成及其性質研究

Abstract

在有機太陽能電池的材料中，製造較高面積的有機-無機材料異質接面是很重要的一環，但是有機與無機材料彼此間的不相容性可能會導致介面間產生空洞而大幅提高電子傳遞的阻礙。 這個研究中，我們發展了一種製備poly(3-hexyl- thiophene) / D-A linker / TiO2混摻材料的合成方法，將二氧化鈦和共軛性高分子以 D-A linker連接起來，藉此避免空洞的產生，同時增加能量傳遞的效率。此D-A linker的分子結構包括三個主要的部分：三乙氧基矽、長烷鏈及可供聚合的噻吩環；當連接劑在二氧化鈦表面形成自組裝單層膜之後，自組裝單層膜末端外露的噻吩環即可當成聚合poly(3-hexyl- thiophene)的起始單元。 我們以電化學聚合與分子自組裝技術為基礎，進一步開發更適合用在有機固態太陽能電池的材料及製程。藉由接觸角量測系統、熱重分析儀、原子力顯微鏡和化學分析能譜儀鑑定自組裝單層膜；再利用原子力顯微鏡和膠體色層分析儀量測此poly(3-hexylthiophene)/D-A linker/TiO2混摻材料的表面性質；紫外光-可見光譜儀和螢光光譜儀所觀察到的現象則被用來闡明此混摻材料的基本光學性質。 在紫外光-可見光譜儀的量測中，我們可以看到無論是成長在TiO2或是自組裝單層膜上的P3HT薄膜其吸光範圍都相同，最大吸收波長皆為620 nm，表示兩者具有相同的conjugation length；但由螢光光譜儀的量測結果，我們卻發現經由自組裝單層膜成長的P3HT薄膜，其PL強度大幅下降，即表示有較高的quenching efficiency，由此證明本方法的確可以能量傳遞的效率大幅提高。此一現象可能是因為D-A linker能以主價鍵結將二氧化鈦和共軛性高分子連接起來，藉此避免空洞的產生，而使光照射後產生之電子與電洞得以迅速的分離，並有效的傳導至兩端電極，進而達到提升元件光電能量轉換效率之目的。 在本研究中，我們合成一系列帶有各種不同長度烷類側鏈基的D-A連接劑，藉由不同長度的側鏈基來調整D-A介面間的距離，進一步探討側鏈基長度對材料性質之影響。

An electron donor (D)/electron acceptor (A) heterojunction was fabricated by depositing conjugated polymers with the aid of a layer of D-A linker on the surface of TiO2. The use of a D-A linker between TiO2 and the conducting polymer enables the formation of a strongly bonded composite, enhancing the efficiency of electron transfer between the donor and the acceptor. This study demonstrates a route for synthesizing novel hybrid materials of poly(3-hexylthiophene)/D-A linker/TiO2. The chemical structure of the molecular linker, which was used to connect chemically organic and inorganic phases, was designed with three main parts - a triethoxysilane group, an alkyl spacer and polymerizable thiophene ring. After the self-assembled monolayers (SAMs) of the linker were formed on the TiO2 surface, the terminal thiophene ring in the linker was used to initiate electro-chemically the growth of poly(3-hexylthiophene) chains electro-chemically for fabricating the novel composite of poly(3-hexylthiophene)/D-A linker/TiO2. The prepared self-assembled monolayers were characterized by contact angle, TGA, AFM and XPS measurements. Both the AFM and the GPC methods were employed to examine the surface morphology of the composites. The efficiency of the photoluminescence (PL) quenching in blends of electron donors and electron acceptors is one of the most important factors that govern the energy conversion efficiency of a photovoltaic cell. PL studies of these new hybrid materials indicate that the quenching efficiency increased as the alkyl spacer length in the D-A linker decreased, perhaps because the surface resistance increases with the length of the alkyl chain. Notably, the presence of the D-A linker between P3HT and TiO2 effectively increases the quenching efficiency of the photoluminescence above that of neat P3HT films on TiO2.