Zinc Silicate Thin Film Composites Obtained by a Sputtering Based Approach: Structural, Dielectric and Photovoltaic Properties

Zinc silicates thin films have been obtained by a solid state two steps reaction, consisting in the sputtering deposition of alternating layers of Silicon and Zinc oxide reagents, followed by their annealing carried out at temperatures ranging from 300° to 560 °C, in air or under vacuum. Transparent and chemically stable amorphous orto- and meta- Zinc silicates, respectively Zn2SiO4 and ZnSiO3 , can guest nanoaggregates of reagents (Silicon and/or ZnO ) depending on a careful modulation of the reaction advancement. Several analysis have been performed to define structural, optical and electrical properties of product thin films, in order to comprehend how obtaining compositions tailored for specific applications, e.g. phosphors, high k dielectric materials, photovoltaic windows, mesoporous photocatalytic materials. In particular, the complete reaction in air gives rise to amorphous Zn2SiO4 thin film, characterized by means of ellissometric method for dielectric properties determination. Moreover, a vacuum environment 450 °C reaction gives n-type transparent composites containing Silicon Quantum dots and Zinc oxide nanocrystals, able to collect photo-generated charge carriers at a very high optical gap (> 2 eV) in p-n junction, and hence useful to fabricate high performance multi-junction photovoltaic solar cells, even in photovoltaic windows architecture.