Flatband Potential of Cadmium Sulfide ( CdS ) Photoanodes and Its Dependence on Surface Ion Effects

Results are presented which show that the flatband potential ( V fb ) of a semiconducting cadmium sulfide ( CdS ) photoanode can be predicted from atomic electronegativity of its constituent atoms. This procedure, previously applied only to metal oxides, now appears generally applicable to any semiconductor‐electrolyte system. The flatband potential was measured in a CdS / S = , OH − /Pt wet photovoltaic cell as a function of S = and OH − concentrations. These measurements showed that the potential‐determining species are HS − and H + . The condition for zero net adsorbed surface charge (PZZP) was also determined by change of solution p S = with added CdS powder and differential potentiometric titration experiments. This is found to occur at a unique S = ion concentration of 4 × 10 − 9 M . The measured flat‐band potential, corrected to the PZZP and for the difference between the Fermi level and the bottom of the conduction band, is in excellent agreement with the value predicted from the atomic electronegativities.