二氧化鈦奈米管陣列的製備與分析及染料敏化太陽能電池的應用

Preparation, Characterization and Application of Titania Nanotube Arrays in Dye-Sensitized Solar Cells

鄭傑中(Chieh-Chung Cheng)

指導教授 ： 蘇昭瑾

國立臺北科技大學/工程學院/有機高分子研究所/碩士(2009年)

https://doi.org/10.6841/NTUT.2009.00195

摘要

染料敏化太陽能電池（DSSC）相對其他種類太陽能電池來說成本較低，也因此成為近來的研究重點。DSSC典型的陽極是由15~20 nm的二氧化鈦奈米粒所組成。然而在電子在TiO2奈米粒間的跳動會降低電子移動，也可能會和電解液發生再結合反應。因此本研究利用陽極氧化法製得TiO2奈米管陣列替代奈米粒以期達到效率提升。
本研究是以鈦金屬基板行陽極氧化反應以得到規則排列的TiO2奈米管陣列。此反應是在二極式電解槽內進行，而以Pt金屬為對電極。電解液則是在乙二醇內添加0.3 wt% NH4F和2 vol% H2O。在15 oC的環境下，控制時間2到8小時以獲得不同管長。但陽極處理後的TiO2奈米管為無結晶相結構，為了得到anatase相的TiO2奈米管，將試片置入高溫爐中，以升溫（降溫）速率1 oC /min（2 oC/min）的速度加熱到450 oC持溫3小時並持續通入氧氣以防氧化膜脫落。
在電池的組裝上，本研究係利用正照光與背照光的方式來檢測太陽能元件。在背照光的應用方法，對電極因為要讓光能通過，勢必要製備透明的Pt對電極。因此我們使用三種不同的對電極來作電池的組裝。分別是以濺鍍法濺鍍1 nm厚的白金電極、H2PtCl6為前趨物的溼式化學法及市售透明對電極。組裝成元件後分別作 I-V特性曲線、IPCE及EIS分析。
為了提高TiO2奈米管的比表面積，本研究以二種不同TiO2前趨物來作奈米管的後處理。將退火處理後的奈米管在60 oC下浸泡0.2 M 的TiCl4 30分鐘，接著用去離子水沖洗後以450 oC 高溫煅燒 30分鐘即完成；另一種則是將正四丁基氧化鈦緩緩滴入2 M的醋酸並持續攪拌五天而形成溶膠狀，將奈米管放入此溶膠中置入水熱罐中以200 oC水熱反應五小時後取出再置入高溫爐加熱450 oC 30分鐘。實驗結果顯示，經過前趨物處理的TiO2奈米管比未經處理的元件有較高的染料吸附量及Jsc進而提升效率值。
而且正照光方面，我們比較同為光陽極同TiO2奈米管，而用不同的照光方式比較。實驗結果發現，背照光的IPCE因為在短波長的區域被電解液吸收，導致光能無法完全利用。所以電流值與正照光方式相比少了將近50 %，效率更相差了將近三倍之多。
最後，我們同為正照方式，比較TiO2奈米管與奈米粒之間的電子傳輸現象。實驗結果顯示，TiO2奈米管確實有效增加電子的傳導，避免電子與電解液發生再結合的反應。

關鍵字

二氧化鈦 ； 陽極處理 ； TiO2奈米管陣列 ； 染料敏化太陽能電池

並列摘要

Dye-sensitized solar cells (DSSCs) are a relatively low cost solar cell technology that has achieved overall light-to electricity conversion efficiencies of over 10%. The electron-collecting layer in a DSSC is typically a 10 μm thick nanocrystalline film comprised of a three dimensional network of interconnected 15–20 nm sized nanoparticles. However the structural disorder at the contact between two crystalline nanoparticles leads to enhanced scattering of free electrons, thus reducing electron mobility. Electron transport is a limiting factor in the performance of these nanoporous nanocrystalline electrodes, hindering progress in achieving higher efficiencies.
This study describes the application of TiO2 nanotube arrays fabricated by anodization of a starting Ti material. The Ti foils were anodized under constant potential in a two-electrode configuration with a Pt foil as a counter electrode at 15 oC using power supply. The anodization electrolyte consists of a mixture of ethylene glycol and DI water (2 vol%) containing 0.3 wt% NH4F. To obtain nanotube arrays with various tube lengthes, the anodization time were varied in the ranges 2 – 8 hrs. After anodization, the as-prepared samples were annealed at 450 oC for 3 hours with heating rate 1 oC/min and cooling rate 2 oC/ min with oxygen ambient for transform amophous TiO2 into anatase.
Backside-illumination is used for TiO2 nanotube array in this study. However, it is necessary to fabricate the transparent counter electrodes which can let sunlight pass through. We used 3 types of transparent Pt electrodes for DSSC assembly. Sputtered Pt electrode with 1 nm of thickness, wet chemical method with H2PtCl6 as a precursor and commercial Pt electrode were compard by I-V curve, IPCE and EIS analysis.
To enhence the specific suface area of TiO2 nanotube, two types of TiO2 precursor have treated after thermal annealing. Annealed TiO2 nanotube array was soaked in 0.2 M TiCl4 at 60 oC for 30 mins and heated at 450 oC for 30 mins in an oven. Tnb was added into 2 M CH3COOH and stirrd for 5 days, then TiO2 nanotube array was put in this sol before 200 oC hydrothermal reaction.
Dye adsorption of TiO2 nanotube array with TiO2 precursor treatement is higher then without one. It provides higher specific suface area to adsorpt dye molecule and higher Jsc.

並列關鍵字

Titanium dioxide ； anodization ； TiO2 nanotube array ； dye-sensitized solar cell

參考文獻

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