硫摻雜二氧化鈦奈米管陣列於染料敏化太陽能電池之應用

Abstract

本論文介紹兩種在二氧化鈦奈米管(TNT)中硫摻雜的方式，來有效提升電子的傳輸效率，並期望進一步提升染料敏化太陽能電池的元件效能。首先我們將陽極處理法成長完之二氧化鈦奈米管燒結至290 °C，再利用水熱摻雜法和電泳摻雜法兩種方式將硫摻雜進去；其中水熱摻雜法利用硫尿(thiourea, TU) 作為硫的前驅物在水熱反應中進行摻雜，隨著TU濃度的提升，可以由XPS看到硫摻雜的含量也會隨之增加，並在濃度為1M時電流密度可以從未摻雜之10.92 mA/cm2上升到11.78 mA/cm2，整體效率由5.77%增為6.35%。而電泳摻雜法將硫的前驅物乙硫醯氨(thioacetamide, TA)與氨水溶液反應產生帶負電之HS-離子，再藉由電泳的方式摻雜入TNT結構中。隨TA濃度的提升，硫摻雜的含量亦隨之增加，同樣也可看到電流密度明顯的提昇，並在濃度為2M時電流密度可上升到11.95 mA/cm2，整體元件效能上由未摻雜之5.65%提昇到6.19%。由IMPS/IMVS量測結果顯示，硫摻雜之TNT的電傳輸能力有明顯的改善，另外由XPS可發現硫以S4+及S6+形式摻雜於結構中，當S6+取代Ti4+後會有陽離子電荷上的差異，可以有效提升二氧化鈦整體結構中的電子載子濃度，進一步提升光電流和整體光電轉換效率。

In this thesis, we report two methods to enhance the high charge-collection efficiency of the device by doping non-metallic element, S, into TiO2 nanotube (TNT) arrays for dye-sensitized solar cells (DSSC). The as-anodized TNT was sintered to 290 °C to remove solvent and organic impurities. At this amorphous phase, it is facile for sulfur doped to the oxygen and titanium defects of TiO2. Here, two post-treatments were carried out to fabricate S-doped TNT, the hydrothermal doping method and electrophoresis doping method. Hydrothermal reactions occured with the sulfur precursor thiourea (TU), inside the as-annealed TNT at 105 °C for 4h. The XPS resuts show that the amount of S increases as increasing the concentration of TU. The DSSC device made of the S-TNT electrode attained efficiency ƞ = 6.35% of power conversion, which is 10% enhanced from the un-doped TNT device (ƞ = 5.77%). In the electrophoresis doping method, theTNT film was immered in the ammonia solution containing sulfur precursor, thioacetamide (TA). The S-doped TNT was fabricated through electrophoresis at a bias potential 0.5V. The S-TNT DSSC shows a significantly improved cell performance compared to that of the un-doped TNT-DSSC (ƞ = 6.19% vs. 5.65%) owing to the much higher Jsc of the former than the latter (11.95 vs. 10.77 mA cm-2). According to the results of IMPS/IMVS, the electron transport properties of TNT-DSSC were improved significantly by doping with sulfur due to the increased electron carrier concentration inducing by substitution of the Ti4 + sites with S6+, which results in an enhanced photocurrent and overall power conversion efficiency.