應用於染料敏化太陽能電池之二氧化鈦奈米管陣列薄膜電極的製備與鑑識

Abstract

本論文提出一個製備染料敏化太陽能電池(Dye-Sensitized Solar Cell, DSSC)工作電極的新方法；導入具有方向性的一維二氧化鈦奈米管(TiO2 nanotube, TNT) 陣列作為工作電極材料，以取代傳統TiO2奈米粒(nanoparticle, NP)之半導體電子傳輸層。我們利用陽極處理法(anodization)於鈦金屬基材上成長有序之奈米管，由於奈米管有序排列地垂直於基材表面，可以提供電子的傳導之一明確的途徑，有效地減少電子-電洞再結合以及暗電流的發生。 我們所提出一Hybrid anodic的新方法可於較短時間內成長出高品質、高膜厚之TNT薄膜。TNT之成長以0.4 wt.% 氟化銨(NH4F)溶解於乙二醇再加入2 vol.% 去離子水作為陽極反應之電解液，並在固定之溫度與反應面積下進行陽極處理反應。陽極處理的第一個小時在定電壓(60 V)條件下進行，此一小時可得到膜厚約為11 um之奈米管；利用此階段於鈦金屬基材上製造出整齊排列的TNT圖案，在後續固定電流密度條件下我們可以得到高品質及線性成長之TNT陣列。 將TNT薄膜浸泡N719染料並組裝成背照式之NT-DSSC元件，我們發現其散射效果隨管長增加而增強；元件之電流值亦隨著TNT管長的增長而有系統的增加，但電壓值則稍為反向遞減。我們的結果顯示，TNT管長增長表面積亦隨之增大，染料吸附量因而增加，此造成元件光電流與整體效能隨管長增長而提升的結果。TNT經TiCl4後處理在管長為43 um，N719染料吸附量為345 nmol cm-2之條件下，我們獲得NT-DSSC之最佳效能為JSC = 14.29 mA cm-2，VOC = 722 mV，FF = 0.67，轉換效率= 6.93%。

To improve the charge-collection efficiency by promoting faster electron transport and slower charge recombination, vertically oriented one-dimensional TiO2 nanotube arrays have been established using the potentiostatic anodization method with promising advance in DSSC applications. Here, we report a novel hybrid anodic method, starting from the potentiostatic anodization followed by a galvanostatic anodization, to grow much longer TNT arrays in a much shorter t. The ordered TNT films were fabricated at 25 oC and active area (6 × 6 cm2) using the hybrid anodic method by anodizing titanium (Ti) foil in the electrolyte containing ammonium fluoride of 0.4 wt.% in ethylene glycol in the presence of 2 vol.% H2O. We found that the lengths of the TNT arrays (L) are linearly dependent on t and controlled by the electric current. The devices made of TNT films show systematically improved cell performance on tube lengths up to ~60 □m, reflecting the excellent intrinsic light-scattering property of the NT-DSSC devices to harvest more sun light with longer TNT arrays. After converting the different tube layers to anatase and sensitizing with Ru-dye (N719), the NTDSSC show a significantly higher photoresponse and conversion efficiencies than tubes formed under self-ordering conditions. We found that the cell JSC with TiCl4 post-treatment increased from JSC = 12.933 mA cm-2 to 14.290 mA cm-2 and efficiency from 6.0 % to 6.9 % at L = 43 um.