Size-Dependent Localized Surface Plasma Resonance of Au Nanoparticles in Au/ZnO Photoanodes for Dye-Sensitized Solar Cells

The size effect of Au nanoparticles on plasmonic ZnO dye-sensitized cells (DSSCs) was investigated. Different sized Au nanoparticles (similar to 5 nm, 10 nm, and 20 nm) were directly deposited on ZnO nanostructures via an in situ reduction technique. The size and the loading of Au nanoparticle were controlled by varying the amount of reducing agent and the reaction time, respectively. By introducing a proper amount of Au nanoparticles into the photoanode, plasmon-enhanced light absorption, photocurrent and power conversion efficiency were demonstrated, with the enhancement increased with decreasing Au particle size. Overloading the photoanode with Au nanoparticles, however, led to a decline in photocurrent and thus the cell efficiency. Au/ZnO DSSCs with optimized film thickness and 5 nm-Au loading attained an efficiency of 3.49%, corresponding to a 59% improvement over that of pure ZnO DSSCs. The improvement in cell efficiency was ascribed to a significant increase in the photocurrent of Au/ZnO devices, as a result of enhanced light harvesting and reduced interfacial resistance in the photoanode.