Abstract
Natural dyes extracted from fruits, vegetables, flowers, and leaves are considered as promising alternative sensitizers to replace synthetic dyes for dye-sensitized solar cells (DSSCs). Generally, solar activity of natural dyes stem from anthocyanin pigment. Carbonyl, carboxyl, and hydroxyl groups present in the anthocyanin molecule improve the adsorption ability of dye on TiO2 and therefore facilitate charge transfer. Here, for the first time, novel natural dyes extracted from St. Lucie cherry, yellow jasmine, and madder berries are reported to act as sensitizer in DSSCs. These novel natural dye extracts are prepared by dissolving related fruits in ethanol. The ingredient of the dyes is identified by FT-IR spectroscopy. Accordingly, FT-IR spectrum reveals that novel natural dye extracts exhibit all the characteristic peaks of anthocyanin pigment. Specifically, St. Lucie cherry consists of more distinct carbonyl group than other sources. Also, photoanodes composed of three TiO2 layers are prepared by using a spin-coating method. Then, they are immersed into natural dyes and analyzed by conducting UV-Vis spectroscopy. Compared with bare TiO2, natural dye-loaded photoanodes demonstrate far higher absorption ability in the visible region. After fabrication of devices with different novel natural dye sensitizers, current-voltage characteristics and electrochemical impedance spectroscopy measurements are performed. The best power conversion efficiency (PCE) of 0.19% is obtained by sensitization of St. Lucie cherry with an open-circuit voltage (V-oc) of 0.56 V, short-circuit current density (J(sc)) of 181 mu A cm(-2), and fill factor (FF) of 0.55. Furthermore, St. Lucie cherry-sensitized devices show the lowest charge transfer and highest recombination resistances. This result can be attributed to the obvious carbonyl group exhibited by St. Lucie cherry.