Wafer‐Scale Semitransparent MoS 2 /WS 2 Heterojunction Catalyst on a Silicon Photocathode for Efficient Hydrogen Evolution

Abstract 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 2 /WS 2 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 2 and WS 2 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 2 /WS 2 /p‐Si photocathode demonstrates outstanding PEC performance, achieving a high photocurrent density of −25 mA cm −2 at 0 V versus reversible hydrogen electrode, along with enhanced stability compared to monolayer MoS 2 /p‐Si. This work provides promising strategies for developing optically transparent, electrically active, and protective catalysts for practical PEC energy conversion systems.