Co3O4/TiO2 heterostructures obtained by hybrid method

The aim of this work is the development of a method for the preparation of periodic surfaces with high-surface-to-volume ratio crystallized in 3D-Opal-like structures made up of Co3O4/TiO2 semiconducting heterointerfaces. These nanostructures, thanks to a peculiar morphology and spatial organization, may be employed in inorganic solar cells to grant both an efficient charge transport at the interface and a higher surface area to enhance the solar radiation absorption. In solar energy conversion TiO2 is a well-known photoactive material, thanks to its chemical and physical properties. However, the width of anatase band-gap (3.2 eV) implies absorption of UV radiation only. Therefore, the coupling with Co3O4, a narrow band-gap p-type semiconductor (Eg?2.07 eV), allows to extend the radiation absorption to the visible range. Here, a hybrid deposition method is presented. It firstly employs a known and economical self-assembly procedure for polystryrene 3D-Direct Opal (3D-DO) crystallization on a conductive ITO substrate. The opal nanostructure is then used as a template pattern for the deposition of TiO2 via ALD (Atomic Layer Deposition) at low temperature. In order to remove the PS template, a thermal treatment (at 450°C in air, 5 hours) of the as-grown ALD-TiO2/PS direct opals is performed and TiO2 hollow anatase nanospheres organized in FCC structures with the (111) plane oriented parallel to the substrate surface are obtained. Finally, the Co3O4/TiO2 heterostructure is obtained through the deposition of Co3O4 via a photochemical method. All samples have been characterized by UV-Vis, XRD, FEG-ESEM, AFM, EDX, and XPS analyses for the optical, structural, morphological and compositional characterization.