Stabilization of CdS and CdSe photoelectrodes modified by a catalyst‐containing polythiophene coating

The protection of CdS and CdSe by a conductive polymer is studied in aqueous solutions of ferrous/ferric redox couple and lithium perchlorate indifferent electrolyte. The polymer is poly(bithiophene) which is grown photoelectrochemically in an acetonitrile solution containing the dimer 2,2′‐bithiophene and lithium perchlorate as the supporting salt. The dimer was chosen as the starting material because photocorrosion of the semiconducting substrate competes with electropolymerization when using a solution of the monomer, leading to very unhomogeneous and poorly adhesive polymers. The protection by the as grown polymer against photodegradation of the semiconductor in an aqueous solution is rather poor, due to a spontaneous reduction of the polymer to its neutral form where its conductivity is lowered by several orders of magnitude. A significant improvement of the protection is obtained by including noble metal clusters on the polymer overlayer. The inclusion is realized by electrochemical reduction of a salt of the metal.