Physical Properties of SnO2/WO3 Bilayers Prepared by Reactive DC Sputtering

Abstract

The combination of transparent and conductive SnO₂ with colored WO₃ thin films has interesting uses in electrochromic windows, photovoltaic cells and photocatalytic systems, where the SnO₂/WO₃ bilayer can improve the device efficiency by increasing the charge separation and extending the energy range of photoexcitation. In this work, SnO₂ and WO₃ thin films were prepared by reactive DC sputtering from Sn and W targets, respectively. Single layers and bilayers deposited on glass substrates have been analyzed by X-ray diffraction, atomic force microscopy, spectrophotometry, and electrical measurements. SnO₂ crystallizes in the cassiterite structure, whereas amorphous WO₃ is obtained on bare and SnO₂-coated glasses, showing higher surface roughness on the SnO₂ layer. Different oxygen vacancy defects have been identified in WO₃ by analyzing photoconductivity transients. The oxygen vacancy defects are responsible for the sub-bandgap absorption that causes coloration in the WO₃ films. Regarding SnO₂, it shows a high transmittance of about 90% in the visible and near-infrared spectral ranges.