Effects of zinc oxide nanostructures on performance of natural dye sensitized solar cells

Abstract

Dye Sensitized Solar Cell (DSSC) is a very promising development in photovoltaic technology. In DSSCs, dye molecules provide the charges, while a semiconductor collects and transports the charge. The performance of DSSCs depend on the choice of nanostructure, semiconductor material and dye type. In this research we investigate the effect of ZnO nanostructures on the performance of DSSCs when sensitized with different natural dyes. We prepared ZnO nanoparticles (NPs), Long ZnO nanowires (NWs) and Long Branched ZnO NW films on Fluorine-doped Tin Oxide Transparent Conducting Oxide (FTO-TCO) glass, and determined their surface morphologies. Analysis software showed that ZnO NPs with a mean diameter of had been deposited, Long ZnO NWs a with mean diameter of and length of had been grown and ZnO NW branches with a mean diameter of and a length of had grown on the parent NWs. Absorbance spectrum of anthocyanin dye extracted from mulberries, chlorophyll dye from spinach leaves and a dye blend in the ratio 1:1 were obtained and analyzed. The blended dye had better absorption features than the individual dyes; it had three absorption peaks one (highest) in the UV zone (363 nm) and two in the visible zone (523 nm and 676 nm) compared to two peaks each for anthocyanin and chlorophyll. It also had the widest full width at half maximum of 117.46 nm compared to 70.20 nm and 74.99 nm for anthocyanin and chlorophyll respectively. We assembled DSSCs using a platinum counter electrode and lithium iodide electrolyte and did I-V characterization. I-V results showed that DSSCs assembled with Long Branched ZnO NW photoanode and sensitized with any of the three dyes always performed better. The blended dye, when used to sensitize any of the three photoanodes, performed better than pure dyes. The best solar cell parameters were obtained when Long Branched ZnO NW DSSC was sensitized with cocktail dye giving open circuit voltage, , short circuit current, and efficiency, . The least performing DSSC was from ZnO NPs sensitized with chlorophyll dye with open circuit voltage, , short circuit current, and efficiency, .