Effect of Thermal Treatment on the Crystallographic, Surface Energetics, and Photoelectrochemical Properties of Reactively Cosputtered Copper Tungstate for Water Splitting

In this Article, we report the effect of postdeposition thermal treatment on reactively cosputtered copper tungstate (CuWO4) thin films and its impact on photoelectrochemical performances. This study indicates that CuWO4 films fabricated at 275 °C were amorphous and did not show significant photoresponse in 0.33 M H3PO4 electrolyte when irradiated with air mass 1.5Global simulated illumination. However, a major improvement in photoelectrochemical performance was observed in identical test conditions after a postdeposition treatment performed at 500 °C in pure argon for 8 h. Indeed, a photocurrent density of approximately 400 μA cm–2 at 1.6 V vs saturated calomel electrode was measured on the annealed CuWO4 samples. Subsequent X-ray diffraction analysis revealed a clear transformation of as-deposited amorphous thin films into a triclinic CuWO4 structure after the annealing step. The polycrystalline CuWO4 films exhibited n-type conductivity, an indirect band gap of 2.25 eV, and a flat-band potential of −0.35 V vs saturated calomel electrode.