以孔洞氧化鋁自組裝二氧化鈦空心半球伴隨二氧化鈦奈米管陣列應用於染敏太陽能電池

Abstract

近年來，染料敏化太陽能電池在再生能源範疇引起廣泛的討論與高度注意。具有高表面積的電極以利染料吸附並獲取更多光子為高效率染敏太陽能電池必需的條件。為了達到此目的，許多團隊致力於電極結構的改良與研發。 利用填充二氧化鈦前驅物入陽極氧化鋁管壁以形成二氧化鈦奈米管，在應用於染敏太陽能電池上展示許多優點。二氧化鈦奈米管沿著陽極氧化鋁管壁生成，藉由陽極氧化鋁管壁的阻隔可有效防止二氧化鈦奈米管互相接觸而延遲電子傳輸，由此可提升電池效率。此外，陽極氧化鋁可防止電子與電解液中電洞再結合的發生。然而陽極氧化鋁與導電玻璃界面間的接合一直是各研究團隊所遭遇到的問題。 許多研究著重在一維二氧化鈦材料用於電極的開發，然而至今仍少有結合一維與空心結構的電極提出。我們團隊提出-陽極氧化鋁模板自組裝二氧化鈦奈米空心半球伴隨二氧化鈦奈米管陣列這樣的結構作為染敏太陽能電池電極。藉由沈積一層鈦於導電玻璃上可增進導電玻璃與鋁的接觸並利於後續的陽極氧化進行。陽極氧化過程中，當上方的鋁已形氧化鋁並反應至下方的鈦，此時二氧化鈦奈米空心半球自發生成。 自主裝二氧化鈦奈米空心半球高約130奈米，寬約200奈米 。利用二氧化鈦前驅物 Ti(OC3H7)4 形成之二氧化鈦奈米管陣列管徑寬200奈米，長700奈米垂直生長於導電玻璃上方，並經確認為銳鈦礦。在經過後續的四氯化鈦處理可增加結構表面積進而提升電池效率。 陽極氧化鋁模板自組裝二氧化鈦奈米空心半球伴隨二氧化鈦奈米管陣列作為染敏太陽能電池電極，可達到短路電流5.00 mA/cm2，開路電壓0.58 V，效率為傳統利用奈米粒子為電極電池的1.77倍。

Dye-sensitized solar cells (DSSCs) have attracted extensive interest in past decade as a promising candidate for the future generation of cost-effective photovoltaic solar cells. It is well-accepted that a high efficiency photoelectrode for DSSCs requires a high surface area for light harvesting. To satisfy this requirement, much effort has motivated recently in development of electrode geometry. TiO2 nanotubes using anodic aluminum oxide (AAO) to backfill the template with TiO2 precursor showed a lot of advantages in DSSC application. TiO2 nanotubes are formed along the channels and separated by isolation alumina. The divided nanotubes without interconnections improve electron transport leading to higher photoefficiencies; plus, the alumina layer slows the recombination of the photo-generated electrons on the TiO2 conduction band and holes in the electrolyte or the oxidized dye. However, the poor contact between FTO (fluorine-doped tin oxide) and AAO may cause a serious leakage of electron transport. While considerable studies have focused on the preparation of 1D TiO2, no methods have been available to combine those with hollow structures. We introduce a novel photoelectrode architecture consisting of self-organized hollow TiO2 hemispheres under porous alumina with TiO2 nanotubes inside. By depositing a thin layer of Ti on FTO substrates before anodization, we improve the contact between FTO substrates and overlaying aluminum; meanwhile, when the aluminum layer is consumed up to the underlying Ti, growth of hollow TiO2 hemispheres under the bottoms of the alumina pores spontaneously occurred. The self-organized hollow TiO2 hemisphere with a height of 130 nm and a diameter of 200 nm was formed. Highly ordered TiO2 nanotube arrays of 200-nm pore diameter and 700-nm length were grown perpendicular to a FTO substrate by infiltrating the alumina pores with Ti(OC3H7)4 which was subsequently converted into anatase TiO2. The structure was treated with TiCl4 to enhance the photogenerated current and then integrated into the DSSC using a commercially available ruthenium-based dye. The dye-sensitized solar cell using self-organized hollow TiO2 hemispheres under porous alumina with TiO2 nanotubes inside as the working electrode generated a photocurrent of 5.00 mA/cm2, an open-circuit voltage of 0.58 V and yielding a power conversion efficiency 1.77 times the conventional nanoparticle-based DSSC.