Highly Stable and Panchromatic Light Absorbing Cs2OsX6 (X = Cl−, Br−, I−) Vacancy Ordered Perovskites as Photoanodes for Solar Water Oxidation

In this work, osmium‐based vacancy‐ordered double perovskites Cs2OsX6 (X = Cl−, Br−, I−) are reported and the role of halides on stability, optical and photoelectrochemical properties is investigated. All these three materials crystallize in a cubic phase like Cs2SnX6 or Cs2PtX6 and possess extraordinary stability in ambient conditions and remain stable in strong acids and bases (from pH 1 to 11). One of the unique properties of these materials is that they show panchromatic visible and NIR absorption (up to 1200 nm) through ligand‐to‐metal [X (Cl−/Br−/I−) to Os] charge transfer and another NIR absorption between 1800 and 2500 nm due to Os d‐d transition. Their pH stability and panchromatic light absorption properties enabled them to be employed as photoanodes in PEC water‐splitting devices. In this work, three osmium‐based vacancy ordered halide perovskites Cs2OsX6 (X – Cl, Br, I) that remain highly stable in acidic and basic media coupled with panchromatic visible light absorption are reported. The stability enabled these materials to be successfully employed as photoanodes for solar water oxidation.