Impact of solvents on the extraction and purification of vegetable dyes onto the efficiency for dye-sensitized solar cells

Abstract

Eight vegetable dyes extracted from flowers, fruits and leaves abundant in the wide biodiversity of the Andes region of South America were extracted with ethanol without purification to explore as vegetable photosensitizers in dye-sensitized solar cells (DSSCs). The absorbance spectra were measured by UV–visible spectroscopy and the photoelectrical performance of the DSSCs based on these dyes with a homemade solar simulator, constructed only for educational purposes under 1 sun of illumination. The open-circuit voltages (Voc) and the short-circuit photocurrent densities (Jsc) varied from 0.39 to 0.48 V and from 0.04 to 0.56 mA cm−2, and the power conversion efficiency (PCE) ranged from 0.01 to 0.18%. Particularly, the highest Voc and PCE values of the DSSCs sensitized by the ethanol extracts of Mortiño fruit (Vaccinium floribundum) and Jamaica flowers (Hibiscus sabdariffa) without purification were presumably associated with anthocyanin, the most effective component present in both vegetable photosensitizers. Hence, various components of the ethanol extracts obtained from these two vegetable dyes were purified by liquid–liquid extraction using different organic solvents of different polarity, namely petroleum ether, chloroform, ethyl acetate, n-butanol, and distilled water. Ethyl acetate resulted as the most favorable solvent for purification of ethanol extracts from Mortiño fruit and Jamaica flowers to use as vegetable photosensitizers in DSSCs. The PCE of the DSSC fabricated with the dye extracted in ethyl acetate from Mortiño fruit achieved 0.33%, with Voc of 0.520 V and Jsc of 1.014 mA cm−2, whereas the corresponding values obtained from the dye extracted from Jamaica flowers reached 0.22% with Voc of 0.541 V and Jsc of 0.678 mA cm−2. Thus, the purification of vegetable dyes used as photosensitizer impacts the photoelectrochemical performance of DSSCs.