High-Density Planar MoSe₂/SnSe Heterojunction for Solar Energy Harvesting and Hydrogen Evolution Reaction

Optoelectronic and photoelectrochemical devices have long suffered from cost and energy-conversion efficiency. A two-dimensional (2D) layered metal chalcogenide (LMC) heterostructure is an optically active sensitizer in optoelectronic and photoelectrochemical electrodes. Here, we demonstrated a technology to fabricate planar heterojunctions by one-step electrophoretic deposition of MoSe₂ nanosheets on regularly spaced indium-tin oxide (ITO) cracks and SnSe nanocrystallines in the gaps. This thin film with grid-like planar MoSe₂/SnSe heterojunction with tunable densities can be produced at a large scale. Unlike the vertically stacked pattern, the product lateral heterojunctions show effective charge transfer and high energy-conversion efficiency simultaneously, as evidenced by the 0.36 V open-circuit voltage, 3.02 mA/cm² short-circuit current density, 55% filling factor, and 0.55% energy-conversion efficiency in the photoelectrochemical cells. In addition, the heterojunctions facilitate the hydrogen evolution reaction (HER) as evidenced by overpotentials of 276 mV at a current density of 10 mA/cm² and Tafel slopes of 84.6 mV/dec in an alkaline medium. The heterojunction density reaches 12.1 junctions per 1000 μm² in the photoanode film. The high density of the heterojunction enables the photoelectric and electrocatalytic performances. The promising results provide avenues for the development of high-power, low-cost optoelectronic, and photoelectrochemical devices.