Hydrothermal Deposition of Metal Sulfide Heterojunction Thin Films for Photoelectrochemical Water Splitting

Metal sulfides represent a broad class of materials with considerable potential for applications in photovoltaic devices and energy technologies. However, the low-temperature synthesis of high-quality metal sulfide thin films remains a formidable challenge. Hydrothermal deposition, known for its versatility and cost-efficiency, has been successfully employed to synthesize a variety of materials, yet its application in the preparation of metal sulfide thin films has not been extensively explored. In this study, we develop a hydrothermal deposition method to synthesize five distinct types of metal sulfide thin films, each with well-defined phases and compositions. As a case study, CdS/Bi₂S₃ thin film was selected and evaluated as photoanode for photoelectrochemical water splitting. Through O-doping and the modification of an ultrathin MoO₃ overlayer, the photocurrent density was significantly enhanced from 1.52 mA cm^-2 (CdS/Bi₂S₃) to 2.27 mA cm^-2 (CdS/O-Bi₂S₃), and further to 2.84 mA cm^-2 (CdS/O-Bi₂S₃/MoO₃) at 1.23 V vs. reversible hydrogen electrode under AM 1.5G illumination. This methodology is expected to advance both fundamental and applied research on metal sulfides.