Enhanced utilization of light through polystyrene microspheres for boosting photoelectrochemical hydrogen production in MoS₂/Si heterostructures

Solar-driven photoelectrochemical (PEC) hydrogen evolution reaction (HER) has attracted widespread attention as a clean and promising renewable energy technology. In particular, the heterojunction formed between n-type MoS₂ and visible light-absorbing p-type Si exhibits considerable potential for PEC-driven HER due to its ability to efficiently separate photogenerated carriers by forming favorable interfacial electric fields. However, a substantial portion of incident light is reflected at the MoS₂/Si planar interface owing to the large refractive index difference, resulting in reduced light absorption efficiency. To address this limitation, two-dimensional polystyrene (PS) microsphere arrays are spin-coated onto the heterostructure, leveraging the Mie focusing (MF) effect to enhance light trapping efficiency. It is found that 1 μm-diameter PS microspheres can enhance the electric field intensity within the Si region by a factor of up to 6.64. Furthermore, oxygen plasma treatment is employed to modify the hydrophobic MoS₂ surface, improving its binding with PS microspheres. This treatment also introduces defects on the MoS₂ surface, which serve as HER active sites. Notably, the photocurrent density of the PS-coupled defective MoS₂/Si (30 W) reaches a peak value of 0.16 mA cm⁻² at 0 V (vs. RHE). This finding highlights the synergistic effects of the PS array and plasmonic treatment, which collectively enhance the performance of the heterostructure through the MF effect, the creation of abundant active sites, and the enhancement of the conductivity. This work underscores the significant potential of PS microspheres and defect engineering in boosting PEC performance, providing novel insights into the development of efficient photoelectrocatalysts.