Jihong Min, Irene Dei Tos, Sepideh Rahimisheikh, Beatriz de la Fuente, Devika Rajagopal, Jan D'Haen, David Cornil, Tom Hauffman, Tom Aernouts, David Beljonne, Joke Hadermann, Byungha Shin, Bart Vermang, Sudhanshu Shukla
ABSTRACT 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 Sb 2 S 3 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/Sb 2 S 3 /NiO x architecture. Photoelectron spectroscopy and computational analysis show a staggered band alignment between Si and Sb 2 S 3 , emulating Z‐scheme charge transfer mechanism. We demonstrate a high performing and stable Sb 2 S 3 ‐Si monolithic tandem for PEC hydrogen evolution reaction (HER) coupled to iodide oxidation reaction (IOR). Under AM 1.5G illumination, the Sb 2 S 3 ‐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.