Fully Textured Monolithic Sb₂S₃/Silicon Tandem for Unbiased and Stable Solar-Driven Water Splitting Paired with...

Solar-driven photoelectrochemical (PEC) production of chemical fuels such as hydrogen is a viable solution to address climate neutrality objectives. Development of a monolithic tandem PEC device consisting of ideal bandgap absorbers is of paramount importance to realize efficient artificial photosynthesis systems. Herein, we report monolithic integration of Sb₂S₃ on textured silicon to realize a completely inorganic and fully vacuum processed multilayer PEC device with Ag/Indium Tin Oxide (ITO)/Heterojunction with Intrinsic Thin layer (HIT) Si/ITO/Au/Sb₂S₃/NiO_x architecture. Photoelectron spectroscopy and computational analysis show a staggered band alignment between Si and Sb₂S₃, emulating Z-scheme charge transfer mechanism. We demonstrate a high performing and stable Sb₂S₃-Si monolithic tandem for PEC hydrogen evolution reaction (HER) coupled to iodide oxidation reaction (IOR). Under AM 1.5G illumination, the Sb₂S₃-Si monolithic tandem device achieves unassisted photocurrent density of 4.38 mA cm^{- 2} with faradaic efficiency of 97% for hydrogen, while maintaining ∼90% of its initial performance after 10 h of continuous operation. These results set a new benchmark for all inorganic monolithic tandems for efficient and sustainable solar-to-chemical conversion. This work unlocks the pathway for artificial photosynthesis systems comprising ideal bandgap photo absorbers.