The Absorption Spectra of Natural Dyes and their Suitability as a Sensitiser in Organic Solar Cell Application

Abstract

This paper analyzes the suitability of organic dyes (hibiscus, Solanum nigrum, beetroot and eggplant) that are locally available in East Africa for low-budget dye sensitized solar cells (DSSC). The natural dyes were extracted in different ways, where the nightshade berries and eggplant were simply crushed and sieved to obtain their juices, while for hibiscus and beetroot, the fruits was boiled in water and then ethanol. The most promising results are found from hibiscus extracted in water at 50˚C, which exhibit a significantly better performance in Umpp (311.35mV), Impp (236.43A) and efficiency (0.43%). The results also show that Solanum nigrum is strong in terms of voltage but poor in terms of current, while Eggplant fails due to a difficult extraction process. Beetroot turns out to be a poor candidate since it contains betanin which does not chelate to the TiO2 surface of the cell. The analysis of Solanum nigrum and hibiscus mixture shows that these mixtures do not lead to a better performance. It is also observed that the process of chelating to the TiO2 shifts the absorption spectra of the dyes slightly towards lower wavelengths. The analysis of the molecular structures of betanin and certain anthocyanins shows the number of =O and -OH groups relative to the total number of atoms per molecule is higher for most anthocyanins, so that they can connect better to TiO2 than betanin.