Studies of dye-sensitized solar cells based on a natural photosensitizer--Anthocyanin.

• Main Authors: Chien, Chiang-Yu, 簡江諭
• Other Authors: Hsu, Ban-Dar
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/6hk9jf

博士 === 國立清華大學 === 生物資訊與結構生物研究所 === 103 === Dye-sensitized solar cells (DSSCs) were fabricated using anthocyanin extracted from red cabbage (Brassica oleracea var. capitata f. rubra), and the conditions that could maximize their performance were explored. The best light-to-electricity conversion efficiency (η) was obtained when the pH and the concentration of the anthocyanin extract were at 8.0 and 3 mM, respectively, and when the immersion time for fabricating sensitized TiO2 film was 15 min. Under low light intensity, the DSSCs sensitized with anthocyanin can keep good VOC and η. More than 40% performance of the TiO2 electrodes sensitized with anthocyanin was maintained after 12 weeks in dark and dry environment, and more than 80% of that was maintained if the anthocyanin was purified. Fabricating the DSSCs in the presence of a coadsorbent, deoxycholic acid, at a molar ratio of dye:coadsorbent of 1:40 was also found to be able to improve the η significantly. The highest η reached was over 1.4%, which is almost three times higher than previously reported conversion efficiencies. In addition, further purification of the anthocyanin extract significantly led to a lower η, and the key elements that greatly affected the performance of the DSSCs based on anthocyanin was found to allocate in the colorless impurities fraction (IPF), which was separated from the purification of anthocyanin extract. Carbohydrates were found to be excellent performance enhancers that functioned in a dose-dependent manner. Different types of carbohydrates generally had different enhancement capabilities in the order of oligosaccharide > disaccharide > monosaccharide > polysaccharide. The enhancement capability was also highly dependent on the constituents of carbohydrates. Two oligosaccharides, isomalto-oligosaccharide (IMO) and xylooligosaccharide (XOS), showed the highest capability. The DSSCs sensitized with them as additives to anthocyanin exhibited a η over 1.6% (an improvement of 60%) with a short-circuit current (JSC) of about 4 mA cm-2, and open-circuit voltage (VOC) around 630 mV. The mode of interaction of anthocyanin with extrinsic carbohydrates was proposed and discussed. The use of carbohydrates and a common coadsorbent deoxycholic acid (DCA) together could induce an additional enhancement, which boosted the η up to 1.87% (an accumulative improvement of 90%). This study provided a choice of a promising and powerful enhancer for the DSSCs based on natural anthocyanins.