The performance of ⟨indium-tin-oxide (ITO)/silicon oxide/n-Si(100)⟩ junction solar cells is improved by immersing Si wafers in a potassium cyanide solution before the ITO deposition. It is found from x-ray photoelectron spectroscopy measurements that about 3&percent; monolayer cyanide(CN−)ions are present on the Si surface after the cyanide treatment. The temperature dependence of the current–voltage curves shows that the band bending inn-Si is increased by the cyanide treatment. The increase in the band bending is attributed to an upward Si band edge shift caused by the presence ofCN−ions at the oxide/Si interface and/or in the oxide layer. Conductance–voltage measurements show that the density of trap states considerably decreases after the cyanide treatment. The conductance decrease is attributed to the passivation of interface states by the adsorption ofCN−ions on Si dangling bonds. ©1997 American Institute of Physics.