Fabrication and characterization of mesoporous SnO2/ZnO-composite electrodes for efficient dye solar cells

Highly efficient mesoporous-composite electrodes were made by a doctor-blade technique from nano-sized SnO2 and submicron-sized ZnO. Coating pastes were prepared by mixing colloidal SnO2 or powdered SnO2 nanoparticles with ZnO submicron particles in the presence of acetic acid, acetylacetone, Triton X-100, and a cellulose thickener. The thickness of SnO2/ZnO-composite electrodes was controlled from 2.6 to 22 mum. The paste using colloidal SnO2 nanoparticles gave SnO2-covered ZnO submicron-sized particles, leading to a high conversion efficiency of the dye-sensitized solar cells (DSCs) at a thickness of 8.8 mm (V-oc = 721 mV, J(sc) = 12.41 mA cm(-2), FF = 0.709 and eta = 6.34%). On the other hand, the use of powdered SnO2 nanoparticles resulted in the formation of mixed large aggregates which were isolated from each other, giving low conversion-efficiency solar cells. The existence of a thin Zn2+ layer on the SnO2 layer of the composite electrode is proposed to explain the improvement in the DSC parameters.