Zinc oxide is a promising material for dye-sensitized solar cells (DSSCs) due to its electronic structure and transport properties, and cells with efficiencies up to 5% have been reported. In order to achieve high efficiency cells, the ZnO nanomaterials properties need to be optimized, which requires a thorough understanding of the synthesis process. We have used sol-gel processing under a variety of experimental conditions to obtain ZnO nanomaterials for application in DSSCs.
In this work, we present two methods for the controlled synthesis of ZnO nanomaterials from ethanol solutions and zinc acetate: forced hydrolysis (with addition of water and NaOH) and auto-hydrolysis (with addition of only water). Special care was taken in preparing ZnO nanopowder due to the tendency of particle growth upon washing and drying. The nanomaterials were characterized using X-ray diffraction and transmission electron microscopy. In both methods, the ZnO nanoparticles size can be controlled in the range of 10 - 30 nm, by changing concentration, time, and temperature.
ZnO nanoparticles of different size, prepared by the two methods, were applied in DSSCs, using both commercial dye (N-719) and organic dyes, such as mercurochrome and eosin-Y. The cell efficiency is strongly dependent on the ZnO synthesis method, dye chemistry, dye sensitization time, and solution chemistry. With N-719 an efficiency of 2% was obtained, while with organic dyes the efficiency was close to 1%. The efficiency is expected to increase by optimizing the cell components.