Fabrication of n–p junction electrodes made of n-type SnO2 and p-type NiO for control of charge recombination in dye sensitized solar cells

The n–p junction electrode fabricated coating nanocrystalline SnO2 thin film with a thin layer of p-type NiO was found to increase the sensitized photocurrent and photovoltage. In addition, increase in the fill factor was noticed due to inhibition of electron back transfer from SnO2 to the redox electrolyte (I3−) by both junction effect and presence of NiO barrier, resulting in much better energy conversion efficiencies. The highest cell efficiency was obtained for the cell fabricated by immersing SnO2 thin films in soluble Ni salts, and converting them to NiO by firing. The optimum NiO coating thickness was found to be only a few angstroms and the energy levels of the excited dye and the conduction band position of NiO suggest that the electron transfer from the excited dye to the underlying SnO2 layer occurs by tunneling through the p-type NiO layer.