染料分子吸附二氧化鈦薄膜之動力學模式與機制及其應用於染料敏化太陽能電池

Kinetic modelling and mechanisms of dye adsorption on TiO2 and its application in dye-sensitized solar cells

劉念慈(Nien-Tzu Liu)

指導教授 ： 楊重光

國立臺北科技大學/工程學院/化學工程研究所/碩士(2009年)

摘要

本論文主要探討染料分子吸附在二氧化鈦薄膜的動力學吸附機制與模式，此吸附過程為製備工作電極的重要步驟，一般製程中通常需要24小時的吸附時間，因此我們以此為動機探討染料吸附量隨著時間的動態變化。
實驗分成兩部份，第一部份為恆溫平衡吸附實驗，使用染料N719、N3、black dye，搭配UV/vis檢測可計算出染料吸附量，發現增加吸附溫度有助於增加薄膜最大飽和吸附量；藉由IR光譜分析，可以觀察染料分子於TiO2薄膜表面吸附機制。第二部份為動態吸附，套用不同的吸附條件，分別為薄膜厚度、染料濃度、吸附溫度在不同吸附時間下進行吸附實驗，結果發現薄膜太厚，造成擴散不易會使染料分子產生吸附不均勻的現象；染料濃度主要影響染料最大飽和吸附量；增加吸附溫度可加快吸附速率。由實驗數據模擬，得此吸附機制符合擬二階動力學模式，並且以化學吸附為速率決定步驟。經由不同的溫度變化可探討熱力學參數熱焓值，證實為吸熱反應。最後將實驗結果應用在染料敏化太陽能電池的組裝，搭配效率測試與交流電阻分析來證實實驗的結果。在此結果發現以0.3 mM的染料N719在55 ℃下吸附薄膜3小時，其效率值較常溫下吸附24小時為佳。

關鍵字

染料敏化太陽能電池 ； 二氧化鈦 ； 染料 ； 恆溫吸附 ； 動力吸附機制

並列摘要

The kinetic models and mechanisms of dye adsorption on TiO2 were discussed in this study. The adsorption process is regarded as a critical step on preparing working electrode. According to the literatures, TiO2 thin film should soak in the dye for 24 hours, yet, the reasons are still unknown. Therefore, we took this necessary step as a motive to discuss dynamic adsorption curve along with time change.
Equilibrium isotherm studies were studied by the effects of initial concentration and temperature for using N719, N3 and black dye. For the adsorption of dye onto TiO2, the results showed that the adsorption processes of the dye onto TiO2 fit with Langmuir isotherm model rather than Freundlich model. Besides, the adsorption of the dyes increased with the raising of the ambiance temperature, which was observed from the intensity of UV-Vis spectra. Moreover, the adsorption condition between dyes and TiO2 surface was investigated by DRIFTs technique.
The operation variables of kinetics adsorption were controlled by the initial dye concentration, film thickness and temperature significantly. The dye capacity increased with the raising of ambience temperature and initial concentration of dyes; however, it decreases with thickness of the film thickness. Furthermore, the adsorption temperature is one of the important factors of the adsorption rate. Sorption kinetic data suggests that the behavior of adsorption kinetics followed the pseudo-second-order model, and the chemical adsorption, determined as endothermic reaction, was the dominating step in the dye-adsorptive processes.
Finally, the results in this study could be applied in dye-sensitized solar cell. Compare to the working electrode adsorbing 0.3 mM dye N719 for 24 hours at room temperature, one immersing in the dye for 3 hours at 55 ℃ inherits the best conversion efficiency in this study.

並列關鍵字

Dye-Sensitized Solar Cell ； TiO2 ； dye ； isothermal adsorption ； kinetic model

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