Preparation of photoelectrodes with spectral response in the visible without applied bias based on photochemically deposited copper oxide inside a porous titanium dioxide film

A soft and simple photochemical technique is proposed for the incorporation of copper oxide to nanoporous TiO₂ with the purpose of sensitizing the TiO₂ to wavelengths in the visible range. An aqueous solution of copper formate is employed as precursor. The light intensity value needed for the process, as well as its spectral range, is readily attainable with solar light. Because of the importance of heterojunctions of porous semiconductors in solar energy application, like extremely thin absorber solar cells, experimental conditions have been studied in order to obtain a thin absorption layer of copper oxide covering the TiO₂. Selection of copper formate solution concentration, irradiation time and previous immersion time in the precursor solution has been studied using X-ray diffraction, scanning electron microscopy and optical spectral transmission. Direction and wavelength dependence of photocurrent show that photons are absorbed by the copper oxide and electrons injected to the TiO₂.