An Investigation of the Power Characteristics in Heterogeneous Electrochemical Photovoltaic Cells for Solar-energy Utilization

A heterogeneous electrochemical photovoltaic cell was constructed using the system of cadmium sulfide(CdS)/sulfides reducing agents//oxidizing agents/platinum. The output power characteristics were investigated focusing upon the redox potentials of the oxidizing agents in the cathodic half-cell and then discussed from the point of view of the solution-electrode junction. Though this type of cell intrinsically has a negative free energy for redox reactions of redox agents in an anodic and a cathodic compartment, it has a characteristic point that a larger open-circuit output than the intrinsical electromotive force determined by a redox couple was obtainable in operation under illumination. For example, in the CdS/S2−/S//Fe2+⁄3+/Pt system we found the open-circuit photovoltage of ca. 2.0 V, which is ca. 83% of a band gap (2.4 eV) of CdS. These measurements showed that a larger open-circuit photovoltage was obtained, though, of course, it was smaller than the band-gap energy of CdS, when the oxidizing agent of the more positive redox potential was dissolved in the cathodic compartment.