Characterization of Plant Based Organic Dye Mixtures for Dye Sensitized Solar Cells (DSSCS) Application

Field: Materials Science (Physical Sciences)

Aims/ Objectives: Main objective. To extract and characterize organic dye mixtures from plant- based chlorophyll and anthocyanin pigments for DSSCs applications. Specific objectives: To extract (solvent extraction process) and mix chlorophyll and anthocyanin dye pigments at varying concentration percentages. To study optical characterization (absorption and transmission) of the varying concentration percentages of the dyes. To fabricate dye sensitized solar cells (DSSCs) from the varying concentration percentages of the dyes and study their I-V characteristics. Study Design: Experimental. Place and Duration of Study: Department of Mathematics and physical sciences, Maasai Mara University, between September 2024 and March 2025. Methodology: Different natural dye mixtures, extracted from Spinacia oleracea (spinach leaves) and Bougainvillaea glabra (red bougainvillaea flower) to obtain the two pigments, chlorophyll and anthocyanin respectively, were blended together at differnt ratios, to establish a mixture with optimum properties and highest efficiency for application in DSSCs. The dye-sensitised solar cell was fabricated where the compact layer was made through spray pyrolysis, followed by depositing TiO2 paste through spin coating on top of the compact layer, and then the coated TiO2 glass electrodes were immersed in dyes mixtures solution for dye pigment to adsorb on TiO2 nanoparticles. Thereafter a counter electrode with two drilled holes was fused together, and electrolyte was fed through the drilled holes. The dye mixtures and the fabricated DSSCs were characterized using UV-VIS spectroscopy and the Solar Cell I-V Test System respectively. Results: Dye sample solutions of chlorophyll and anthocyanin were extracted via solvent extraction, filtered and then mixed in different ratios. The plant products used were analysed to check if they had the required pigments (chlorophyll and anthocyanin). The dilution of the known concentrated dye (ruthenium complex dye) to different solution concentrations was done, and their absorbance characteristic were determined. The absorbance data of the ruthenium dyes showed the highest absorbance values within the visible light region at 437 nm, and the absorbance of the chlorophyl and anthocyanin solutions were determined at the same wavelength of 437 nm. The transmittance of the dye mixtures and the standard ruthenium dye was done, where ruthenium had the least transmittance, indicating that it permits less amount of light to penetrate past the dye within the visible light region. Furthermore, the dye absorption curves were determined by the UV- VIS spectrophotometer, which showed that mixing chlorophyll and anthocyanin increases the range of light absorption. The optical characterization of the annealed thin films was done, and the transmittance spectra for the compact layer and annealed TiO2 films displayed a gradual increase in transmittance within the visible light range, indicating that visible light transmits very well through the film, which is an excellent feature for solar cells in harvesting visible light from sun. The film thickness of the annealed compact and TiO2 layer was determined using a DEKTAK- Profilometer. Compact layer size was determined and its effect on the functionality of the DSSC was discussed. Current-voltage (I-V) Characteristics of the DSSC were measured at room temperature to determine the effects of Chlorophyll dye, anthocyanin dye, and their mixtures on the DSSC’s ability to harvest visible light. It was found out that pure anthocyanin dye led to higher efficiency compared to all other dyes since it has a wider spectrum range for absorbing visible light and chlorophyll had the lowest absorption spectrum range of visible light hence the lowest cell efficiency. Furthermore, mixtures’ efficiencies depend on the amount of anthocyanin present, and thus higher quantity of anthocyanin leads to higher efficiency compared to chlorophyll. Conclusion: Transmittance and absorbance characteristics of the dye mixtures assisted in establishing the amount of light each mixture absorbed. Electrical characterization, such as ISC, VOC, and PM, was calculated at room temperature. This research emphasized on investigating the2 properties of different dyes mixtures and came up with a mixture of the best properties.