FormationofsilicananolayersonZnOelectrodesindye-sensitizedsolarcells

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_∞) 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 μrns ^-1, thinner SiO₂ layers could be formed on the zinc oxide particles and a high Jsc 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.