Photosensitization of Semiconductor Electrode by Cyanine Dye in Lipid Bilayer

Abstract

A thin film electrode is prepared by evaporation of indium‐tin‐oxide. It is covered by a bimolecular layer of lipid doped with a cyanine dye in direct contact to the electrode. The assembly is investigated in an electrochemical cell. The bilayer lowers the voltage dependent capacitance corresponding to the effect of a thin homogeneous dielectric with a hole fraction of about one percent. Illumination leads to a sensitized photocurrent which is enhanced by thiourea. The maximal yield at saturating potential and 3M thiourea is 0.7. The electron is transferred at a rate of about 1010 sec−1 and a yield of 0.8. An intermediate is formed consisting of the oxidized dye and an electron at the electrode surface. Supersensitization is due to the reduction of this intermediate by thiourea, the drop of current at low potentials is assigned to a reduction by occupied surface states.