二氧化鈦薄膜孔洞大小控制及其對染料敏化太陽能電池之影響

Abstract

染料敏化太陽能電池(Dye-sensitized solar cell, DSSC)是目前極具發展潛力的新一代有機太陽能電池。其中光電極之孔洞形貌是影響效率的主因之一。因此孔洞大小、比表面積，以及孔隙率，皆是優化染料敏化太陽能電池效率的研究重點。 本論文利用聚乙二醇高分子團聚的特性，在製作二氧化鈦光電極時，以100oC的溫度對試片進行熱處理，此”團聚處理”可以使得聚乙二醇由界面活性劑的角色轉化為類似起孔洞劑的效果，而經過高溫燒除之後得到比較大孔洞的二氧化鈦薄膜。藉由控制團聚處理時間，可以得到一系列孔洞大小，但表面積與孔隙率極相似的光電極。進而探討二氧化鈦光電極孔洞之大小，在液態與膠態電解質下，對效率的影響。 由光電轉換效率及電化學阻抗之檢測，發現較大的孔洞可使電解質在光電極中擴散較好而讓光電流提升導致更佳的光電轉換效率。最適當的孔洞大小則視電解質成分等因素而定。本實驗中利用液態電解質在其最適當之孔洞大小下，效率可提升8.8%達到6.68%的光電轉換效率；而膠態電解質更可以提升13.6%，而使效率達到7.43%。

Dye-sensitized solar cell (DSSC) is a new generation organic solar cell which has tremendous market potential due to its low cost, flexibility as a device, and indoor usage etc. The pore morphology of TiO2 film has been recognized as one of the major factors influencing the conversion efficiency of DSSC. As a result, the pore properties such as surface area, porosity, and pore size/distribution have been fervently studied in order to improve the conversion efficiency of DSSC. In this study, we have developed an aggregation process of polyethylene glycol (PEG) at 100 oC isothermally using different treatment time to modulate the pore size of TiO2 films, while keeping their surface area and porosity about the same. This process transforms the role of PEG from a surfactant to a porogen to form larger pore after long aggregation time. The effect of pore size /distribution of TiO2 films on DSSC performance was further examined using liquid electrolyte (LiI) and gel electrolyte (AEII) under 30w% PEG loading. Based on the I-V characteristic and electrochemical impedance spectroscopy analysis,larger pore can improve redox couple diffusion in TiO2 porous electrode to raise photocurrent, resulting in enhanced conversion efficiency. Under each optimized pore size, the liquid electrolyte exhibits η=6.68% with 8.8% improvement (over the film without aggregation process) and the gel electrolyte shows η=7.43% with 13.6% enhancement, respectively.