Highly Stable and Panchromatic Light Absorbing Cs<inf>2</inf>OsX<inf>6</inf> (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.