Tungsten Oxide-Based Thin Films Prepared by Physical Vapor Deposition Techniques for Photoelectrochemical Water Splitting: A Review

The global energy demand has raised concerns about environmental sustainability and economic stability. This has led to significant efforts to identify renewable and green energy sources. Hydrogen production through the water splitting reaction offers a promising pathway, since it yields hydrogen and oxygen as by-products. The photoelectrochemical technique has emerged as one of the effective methods for water splitting, offering vast potential for hydrogen production on a large scale. Among the various semiconductor photoelectrodes, tungsten oxide (WO₃) has attracted considerable attention due to its suitable band gap, good chemical stability, and strong absorption in the visible region. This review addresses the fabrication of WO₃-based thin films prepared using physical vapor deposition (PVD) techniques, including thermal evaporation, sputtering, pulsed laser deposition (PLD), and electron-beam evaporation. Reported studies highlight that sputtered WO₃ films often achieve high photocurrent densities and improved crystallinity, while PLD enables precise control over stoichiometry and nanostructure. Nevertheless, key challenges persist, such as controlling stoichiometry and phase stability, charge-carrier recombination, limited light absorption due to the wide band gap, low conductivity, and structural defects. The review concludes strategies to overcome these limitations, such as conducting thermal and electron-beam evaporation, combining CVD and PVD techniques, and optimizing sputtering conditions.