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.