Cu S films as photoelectrodes for visible-light water splitting

Copper sulfides are appealing semiconductors for optoelectronics applications requiring visible-light activity, such as solar water splitting, due to their relatively low band gaps and earth-abundance. This study investigates the effect of deposition conditions, including substrate temperature and background gas pressure, on the characteristics and photoelectrochemical performance of copper sulfide (Cu x S) films grown by pulsed laser deposition (PLD) on Si (100) substrates. The results reveal that varying the deposition parameters influences the crystalline phases, morphology, and optoelectronic properties of the films. For deposition at room temperature, the films exhibited covellite CuS phase, while elevated deposition temperatures (250 °C and 500 °C) led to the formation of Cu 1.8 S and Cu 2 S phases, resulting in narrowing of the band gap, with the increased temperature also enhancing the film crystallinity and surface roughness. As a result of the changes in film morphology and crystal structure, photocurrent density magnitudes increased with higher deposition temperatures, reaching 0.747 mA/cm 2 at −0.8 V for films deposited at 500 °C under vacuum, at least an order of magnitude higher than reported in comparable previous studies of the photoelectrochemical performance of Cu x S. Background gas pressure only slightly affected the photocurrent density, with changes in photoactivity also correlating with changes in film roughness and band gap. The results demonstrate the good visible-light activity and behavior of Cu x S as a stand-alone photoelectrode material, with tunability based on the fabrication conditions, suggesting their potential use in photoelectrochemical and other solar energy conversion applications. • The study examines how deposition parameters, such as substrate temperature and background gas pressure, influence the properties and photoelectrochemical performance of Cu x S films grown by PLD. • Increasing deposition temperature (to 250 °C and 500 °C) led to the formation of Cu 1.8 S and Cu 2 S phases and narrowed band gaps, improved crystallinity and increased surface roughness compared with deposition at room temperature. • Photocurrent densities increased with higher deposition temperatures, reaching 0.747 mA/cm 2 at −0.2 V RHE for films deposited at 500 °C under vacuum. • The Cu x S films exhibit excellent visible-light activity and tunability, demonstrating their potential for photoelectrochemical and solar energy conversion applications. • This study provides insights into the behavior of Cu x S as an independent photoelectrode and how its performance may be optimized when used in heterostructures to enhance PEC performance.