International Journal of Hydrogen Energy, Vol.45, No.15, 8676-8685, 2020
Band gap optimization of tin tungstate thin films for solar water oxidation
Semiconducting ternary metal oxide thin films exhibit a promising application for solar energy conversion. However, the efficiency of the conversion is still limited by a band gap of a semiconductor, which determines an obtainable internal photovoltage for solar water splitting. In this report the tunability of the tin tungstate band gap by O-2 partial pressure control in the magnetron co-sputtering process is shown. A deficiency in the Sn concentration increases the optical band gap of tin tungstate 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 the highest photoelectrochemical activity. In particular, a maximum photocurrent density of 0.375 mA cm(-2) at 1.23 V-RHE and the lowest reported onset potential of -0.24 V-RHE 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 is of paramount importance for application. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.