Institute of Fundamental Technological Research

Semiconducting ternary metal oxide thin films exhibit a promising application for solarenergy conversion. However, the efficiency of the conversion is still limited by a band gapof a emiconductor, which determines an obtainable internal photovoltage for solar watersplitting. In this report the tunability of the tin tungstate band gap by O2 partial pressurecontrol in the magnetron co-sputtering process is shown. A deficiency in the Sn concentration increases the optical band gap of tin ungstate thin films. The optimum band gap of 1.7 eV for tin tungstate films is achieved for a Sn to W ratio at unity, which establishes thehighest photoelectrochemical activity. In particular, a maximum photocurrent density of 0.375 mA cm^2 at 1.23 VRHE and the lowest reported onset potential of -0.24 VRHE for SnWO4 thin films without any co-catalyst are achieved. Finally, we demonstrate that a Ni protection layer on the SnWO4 thin film enhances the photoelectrochemical stability, which isof paramount importance for application.

thin film, tin tungstate, reactive magnetron sputtering, photocurrent density, thickness band gap