Effect of Doping and Co-sensitization on the Photovoltaic Properties of Natural Dye-sensitized Solar Cells

The fabrication of dye-sensitized solar cells was successfully carried out using the Dr. Blade deposition method on transparent Fluorine-doped Tin Oxide (FTO) coated glass substrates with a sheet resistance of Ω16.6/sq. The natural dyes used in this research were extracted from bitter leaf (chlorophyll pigment) (vernonia amygdalina), Zobo (anthocyanin pigment) (roselle) plant and a mixture of both dyes using ethanol as the extraction solvent. 50 g of each blended bitter leaf and zobo leaf were separately extracted in 250 ml of ethanol using a beaker. 25 g each of both dyes was adequately mixed and extracted in another 250 ml of ethanol inside a beaker. The cell was fabricated using lead as the counter electrode, nanocrystalline Titanium (IV) Oxide as the photoelectrode and potassium iodide as the electrolyte. 0.01 mol of hydrated nickel dichloride was used in doping the TiO2 nanoparticles. The XRD pattern showed irregular polycrystalline thin films with fairly randomly oriented peaks. Intense and narrow peaks were seen at (110) and (311) orientation for the film corresponding to 2θ values of 25.34o and 68.77o, respectively. Optical characterizations of the fabricated cells were carried out using UV-Vis (UV-1800) spectrophotometer. It was seen that all the nickel-doped dyes showed a moderate absorption peak of 40% in the UV region of the electromagnetic spectrum. A solar simulator was used for the I-V characterizations of the fabricated cells at an illumination intensity of 881mW/cm2 . The combined chlorophyll and anthocyanin-based dyes, which gave the highest conversion efficiency of 1.63% and the least energy band gap of 1.92 eV, were seen to be more efficient than the two lone dyes with efficiencies of 0.31% and 0.40% for the anthocyanin and chlorophyll-based dyes respectively. The observed high efficiency of the co-sensitized dyes implies the dye synergic absorption effect due to co-sensitization. It also suggests that 0.01 mol of the nickel dopant increases the electrical characteristics of the combined dyes.