Enhanced photocatalytic hydrogen production via optimised ZnO–SnO₂ thin films: the role of sputtering conditions

ZnO – SnO₂ films were deposited using a sputtering technique, with variations in the working pressure and resilience time during heat treatment. The synergy between the power density used for Sn deposition and the working pressure facilitated the formation of different crystalline phases of Sn, including tetragonal and orthorhombic SnO₂, face-centered tetragonal Sn, tetragonal SnO, and Zn₂SnO₄. Variations in the working pressure and resilience time affect the presence of defects and impurities in the ZnO – SnO₂ films, thereby influencing their photocatalytic hydrogen production capabilities. The highest hydrogen production was observed in films containing several defects related to oxygen vacancies, oxygen vacancies in SnO₂ , and emissions at deep levels, as confirmed by photoluminescence measurements. These emissions are favored by the intermediate states formed between the valence and conduction bands of the semiconductor, acting as electron traps or recombination centers, which enhance the photocatalytic performance of the ZnO – SnO₂ films.