The photovoltage and the fill factor of (indium-tin oxide (ITO)/silicon oxide/polycrystalline n-Si) junction solar cells are increased by immersing Si in a potassium cyanide solution before the deposition of an ITO film. Measurements of the temperature dependence of the dark current-voltage curves show that the mechanism of the current flow through the Si depletion layer is changed from trap-assisted multistep tunneling to thermionic assisted tunneling by the KCN treatment, indicating a decrease in the density of the trap states in the Si depletion layer. Measurements of the electrode conductance also show that the trap density is greatly reduced by the KCN treatment. The improvement of the electrical characteristics is attributed to the decrease in the trap density and an increase in the barrier height in n-Si caused by the inclusion of cyanide ions at the oxide/Si interface and/or in the silicon oxide layer.