Nanostructured ZnO with bio-capping for nanofluid and natural dye based solar cell applications

In this paper we report the synthesis of ZnO nanoparticles using oxalic acid and the enhancement in its properties through surface modification by bio-capping using the medicinal plant Scorparia dulcis. The surface modified nanomaterial shows improved optical and morphological properties. It also exhibits enhanced near band edge ultraviolet photoluminescence and markedly reduced green emission. The perfect surface passivation with reduction in oxygen vacancies has resulted in the significant change in photoluminescence. Thermal conductivity measurements have been carried out in the base fluids water and ethylene glycol for different weight percentages of nanostructured ZnO. Significant increase in thermal conductivity ∼10–50% is observed for the nanofluids obtained using the surface modified particles. Photo conversion efficiency has been studied for natural dye based solar cells using bio-capped ZnO for the first time. Improved efficiencies of 10–30% are observed for solar cells sensitized using the natural dyes extracted from Jamun, marigold, pomegranate and mangosteen.