Effect of oxygen pressure on pulsed laser deposited WO3 thin films for photoelectrochemical water splitting

Abstract

Tungsten oxide (WO3) thin films on fluorine-doped tin oxide (FTO) coated glass substrates are fabricated by pulsed laser deposition for photoelectrochemical water splitting. The effects of oxygen pressure during deposition on the structure, morphology, optical properties and photoelectrochemical performance of the films have been systematically evaluated. Columnar growth characteristic of WO3 thin films is observed at oxygen pressure higher than 8 Pa. The grain size increases with increasing oxygen pressure in the range of 1–13 Pa then decreases with further increasing oxygen pressure from 13 Pa to 30 Pa. Pure monoclinic phase of WO3 has been obtained for samples deposited above 13 Pa. Decreasing oxygen pressure below 8 Pa leads to an oxygen deficient surface with a substoichiometric phase. The film prepared at 13 Pa exhibits the best photoelectrochemical performance with a photocurrent density as high as 1.9 mA/cm2 under a xenon lamp illumination in 0.1 M Na2SO4 electrolyte. Furthermore, hydrogen evolution conducted with a three-electrode configuration and a two-electrode configuration is presented and discussed.