Wafer-Scale Semitransparent MoS/WS Heterojunction Catalyst on a Silicon Photocathode for Efficient Hydrogen Evolution.

The development of catalysts that are optically transparent, electrically charge-transferable, and capable of protecting underlying photoactive semiconductors is crucial for efficient photoelectrochemical (PEC) hydrogen production. However, meeting all these requirements simultaneously poses significant challenges. In this study, the fabrication of a wafer-scale transparent bilayer MoS/WS catalyst is presented with a staggered heterojunction, optimized for photon absorption, extraction of photogenerated charge carriers, and surface passivation of p-Si photocathode. The MoS and WS monolayers are grown via metal-organic chemical vapor deposition, followed by sequential transfer and stacking onto the p-Si photocathode. The resulting type-II heterojunction film establishes a strong built-in electric field for rapid charge carrier transport and effectively protects the Si surface from oxidation and corrosion. The fabricated MoS/WS/p-Si photocathode demonstrates outstanding PEC performance, achieving a high photocurrent density of -25 mA cm at 0 V versus reversible hydrogen electrode, along with enhanced stability compared to monolayer MoS/p-Si. This work provides promising strategies for developing optically transparent, electrically active, and protective catalysts for practical PEC energy conversion systems.