洋菜膠態電解質型染料敏化太陽能電池

Abstract

染料敏化太陽能電池(Dye-sensitized solar cell, DSSC)因為具有低價格、可撓曲及適合室內使用之特性而成為目前極具發展潛力的新一代有機太陽能電池。而膠態電解質因為擁有較固態電解質好的離子傳輸能力及優於液態電解質之穩定性，所以成為染料敏化太陽能電池效率的研究重點之ㄧ。為了避免環境之汙染，高分子多醣類之天然化合物則被利用做為液態電解質之固化劑使用。 本論文利用天然物洋菜作為膠態電解質支撐物，然而洋菜膠態電解質之表現在以往研究上並無法與液態電解質相比，因此本論文將利用(1)低毒性之有機溶劑及(2)低黏度離子液體 (3)調整TiO2薄膜之孔洞，三種方法改善此洋菜電解質之效能。 在使用對環境較友善之dimethyl sulfoxide (DMSO)/ propylene carbonate (PC) (體積比=1:4)雙溶劑系統下，可得到導電度14.2 mS cm-1、離子擴散係數為2.7×10-6 cm2 s-1之洋菜膠態電解質，其電池之光電轉換效率3.4 %。比較未使用洋菜之效能仍維持80% 光電轉換效率，而在電池效率上則比未使用雙溶劑系統前提升2.4倍之效率(1.4 % to 3.4 %)，；使用以1.5M 1-allyl-3-ethylimidadolium iodide(AEII)取代1-methyl-3-propylimidadolium iodide (MPII)及0.65 wt%之洋菜製備之電解質可得到與3-methoxypropionitrile (MPN)液態電解質可相比擬之電池之光電轉換效率(5.89 %，MPN電解液為5.84%)；為了得到較大孔洞之TiO2薄膜，在TiO2 漿料中加入30% 的PEG並在100℃下維持一小時，此TiO2薄膜讓此使用此低毒性洋菜電解質之太陽能電池之效率7.43 %，比較未添加PEG的電池提升了26%。利用此三個方法使得洋菜膠態電解質可使其效率大幅度改善且高於以MPN為溶劑之液態電解質。

Dye-sensitized solar cell (DSSC), a new generation organic solar cell, has tremendous market potential due to its low cost, flexibility as a device, and indoor usage. Recently, gel electrolytes are highly pursued for DSSCs because of its better ion transport ability than the solid electrolyte and its better stability than liquid electrolyte. Moreover, natural materials such as polysaccharides have been attempted to gel the liquid electrolytes of DSSCs to prevent environmental pollution. In this thesis, a natural agarose is chosen as the matrix of the gel electrolytes, whose performance and the efficiency of DSSCs still require much improvement compared to liquid electrolytes. Furthermore, three approaches were employed to enhance the performance of aragose gel electrolyte-based DSSC: (1) using environmentally benign solvents, (2) utilizing the low viscosity ionic liquids, and (3) modifying the pore size of TiO2 films. On the environmentally benign solvents, the electrolyte containing the co-solvent of 80 vol.% propylene carbonate (PC) and 20 vol.% dimethyl sulfoxide (DMSO) yielded the highest conductivity, 14.2 mS cm-1, and the highest diffusion coefficient of triiodide, 2.7×10-6 cm2 s-1. Its conversion efficiency with agarose was of 3.4%, which retained ~80% of the energy conversion efficiencies of the reference cell without agarose. Yet, it was 2.4 times improvement compared to pure 1-methyl-3-propylimidadolium iodide (MPII) with agarose (1.4%) under the illumination at AM 1.5, 100 mW cm-2. The efficiency of the DSSC using the agarose gel electrolyte containing ionic liquid, 1.5 M 1-allyl-3-ethylimidadolium iodide (AEII) and 0.65 wt% agarose is 5.89 % with the highest I3- diffusion coefficient of 7.7×10-6 cm2 s-1. The performance of the AEII ionic liquid-based agarose gel electrolyte is comparable to the liquid electrolyte based on 3-methoxypropionitrile (MPN) (5.84 %). Finally, Using the optimized TiO2 film with larger pores (30% PEG loading, 100 °C /60 min), an efficiency of 7.43% is achieved for the agarose gel electrolyte-based DSSC, which represents a 26.1% improvement over TiO2 without the addition of PEG. The approaches mentioned above have made the performance of agarose gel electrolyte higher than the MPN-based electrolyte.