TiO₂-CuO three-dimensional heterostructure obtained using short time photochemical deposition of copper oxide inside a porous nanocrystalline TiO₂ layer

Solid inorganic three-dimensional nanocrystalline heterostructures are being studied lately, particularly, regarding photovoltaic structures and as a possible alternative to a solid dye sensitized solar cell (DSSC). Unbiased electron injection from copper species to porous nanocrystalline TiO₂ has been reported recently for TiO₂-copper oxide photoelectrodes immersed in an aqueous electrolyte; demonstrating that relative position of band edges of these two nanocrystalline semiconductor oxides under illumination encourages pursuing a three-dimensional nanocrystalline TiO₂-Cu_xO heterostructure. Here, copper oxide deposition inside a porous nanocrystalline TiO₂ film using a more efficient photochemical deposition technique is studied further and described. Samples obtained using UV-radiation incident through the conducting glass substrate and samples radiated from the TiO₂ side are prepared and studied. Relative concentration of copper species in the TiO₂ surface layer is analyzed using Rutherford backscattering spectrometry (RBS). Comparison of both sample types gives an idea of copper species distribution along the incident direction of the reaction-provoking UV-radiation. XPS analysis of TiO₂ surface was used to determine oxidation state of copper species present, as well as, their relative proportions. AFM images and roughness analysis clearly show the effect of the dependence of UV-radiation absorption with penetration distance. Finally, the photocurrent dependence with time corresponding to both sample types is studied, compared and explained.