P-CuO films and photoelectrochemical corrosion

Abstract

CuO films on transparent, conductive substrates (fluorine doped tin oxide, FTO), obtained by spray pyrolysis, were analyzed photoelectrochemically in neutral and alkaline solutions. The photoresponse was typical for a p-type semiconductor in a junction with an electrolyte. In absence of an electron scavenger in solution, cathodic photocurrents decayed rapidly (within minutes). This is ascribed to photogenerated conduction band electron initiated reduction of the electrode material to Cu2O. Such films could be reactivated by annealing in air, which resulted in the reconstruction of the CuO phase and complete recovery of photocurrents. Reducible species (methylviologen, ferricyanide, oxygen) were added to the electrolyte in order to compete with the photoelectrochemical auto-reduction of the semiconducting layer. In the case of O2 as scavenger, formation of a product in solution, H2O2, was observed, although with a Faradaic efficiency of only 2 percent. In all cases, only minor long-term stabilization was achieved. This was because sufficiently high concentrations of electron scavengers could not be used when high cathodic dark currents were developed (case of ferricyanide), or when the solubility was limited (case of oxygen). In addition, reduction of the semiconductor by the reduced photoactive species (case of methylviologen) can occur.