Light management in TiO2 thin films integrated with Au plasmonic nanoparticles

The light-harvesting properties of metal oxide thin films can be remarkably increased by the introduction of èplasmonic nanostructures, leading to higher efficiencies in photovoltaic or photoelectrochemical devices. In the prototypical material combination, Au-TiO2, nano- and mesoscale porosity of TiO2 is desirable to improve not only the light-harvesting, but also the available surface area for chemical reactions. Moreover, great attention has been given to the control of size and shape of Au nanoparticles (NPs) to increase the overall optical properties of the film. In this work, we investigate the optical properties of the composite Au-TiO2 films exhibiting remarkable light scattering properties. TiO2 is characterized by a tree-like hierarchical morphology produced by pulsed laser deposition, and two different configurations for Au integration, namely Au on top and at the bottom of TiO2 are explored by varying the size of Au NPs. The hierarchical oxide morphology allow to achieve superior scattering properties after the combination with Au NPs with respect to films obtained from a commercial paste deposition. Both the Au-top and Au-bottom configurations enable to tune the plasmonic properties of Au NPs. Specifically, outstanding scattering properties are exhibited by the composite TiO2 film grown on top of large (~100 nm) Au NPs. These results show the potential interest of employing such integrated films as photoanodes in dye-sensitized or perovskite-based solar cells, or in photoelectrochemical cells for water splitting. An analogous approach can be employed for alternative materials, both considering the plasmonic structures as well as the semiconductor layer.