Ceramic Layers for Solar-Driven Energy and Environmental Applications

Abstract Solar-driven processes may represent a key solution for the current energy and environmental issues. This PhD thesis was focused on two main fields of interest, energy production by Dye-sensitized Solar Cells (DSCs) and environmental preservation through the photocatalytic degradation of pollutants. TiO2 is the reference material for these applications, due to its superior performance as DSC photoanode and as photocatalyst, for which it is widely used in the form of nanocrystalline supported layers. This work was aimed at the production of optimized ceramic layers for the afore-mentioned applications. Screen-printing was considered as deposition technique due to its high reliability and scalability. The process optimization is a crucial step for obtaining high-performance layers, and the key parameter is the quality of the screen-printing ink. The first part of the study was then focused on a comprehensive study on the ink composition and processing, and the correlation with its rheological properties and the characteristics of the deposited layers. The acquired knowledge was used to develop inks for the specific applications. Firstly, a novel doping route for the production of semiconductor oxide layers was studied. This approach consisted in adding a metal precursor to the ink based on pre-formed nanopowder, in order to promote the doping in-situ during the thermal treatment of the layers. Zr was selected as model dopant due to its beneficial effects for both the considered applications. The procedure was developed by considering different amounts of dopant and sintering temperatures, then it was validated through extended XRD and TEM characterizations. The properties of the layers were deeply investigated and finally their performance as DSC photoanodes and photocatalytic layers were assessed. Secondly, a dedicated study on the role of water in TiO2 inks for DSCs was conducted. This component resulted to have a fundamental dispersing action for TiO2 nanoparticles, for which a specific mechanism was hypothesized. This effect favored an improved rheological behavior of the inks and optimized properties of the derived layers. Finally the most suitable amount of water, which produced enhanced device performance, was defined. The conclusive section of the thesis involved the preliminary study of an alternative photoanode material for DSCs photoanodes, i.e. Ti-substituted Hydroxyapatite (TiHA). Nanopowder with different Ti amounts were subjected to compositional, structural, electronic and functional characterizations, in order to determine their suitability for the target application. Inks and photoanodes were then developed. Finally, TiHA-based DSCs were tested and the applicability of the novel material was demonstrated.