Formation of Silica Nanolayers on ZnO Electrodes in Dye-Sensitized Solar Cells

Zinc oxide electrodes for use in dye-sensitized solar cells were coated with thin silica layers by using a sol-gel transformation of tetraethylorthosilicate (TEOS). Coating solutions were prepared by mixing TEOS and diluted ammonia while stirring and ultrasonificating simultaneously. Two kinds of coating methods (immersing and dip-coating) were adopted and compared to control the thickness of the silica layers on a nanometer scale. With the immersing method a relatively thick SiO2 coating was made on zinc oxide particles on the electrodes, which resulted in an increase in the open-circuit photovoltage (V-oc) and a large decrease in the short-circuit photocurrent density (J(sc)). In contrast, by using the dip-coating method, with a relatively low withdrawal speed of 100 mu m s(-1), thinner SiO2 layers could be formed on the zinc oxide particles and a high J(sc) as well as a high V-oc was obtained. These results demonstrate that the V-oc characteristics of solar cells using silica-coated zinc oxide electrodes can be enhanced by controlling the structure of the silica-coating layers.