Highly Conductive Ligand‐Free Cs2PtBr6 Perovskite Nanocrystals with a Narrow Bandgap and Efficient Photoelectrochemical Performance

Abstract Design of high‐performance all‐inorganic halide perovskites, especially lead‐free perovskites, is key to the broadening of its application prospects. Herein, the authors report the synthesis of ligand‐free cesium platinum (IV) bromide nanocrystals (Cs 2 PtBr 6 NCs), a new kind of vacancy‐ordered lead‐free perovskite nanomaterial, by a facile one‐pot method. The Cs 2 PtBr 6 NCs exhibits a narrow band gap of 1.32 eV covering the entire visible range, which is supported by density functional theory calculations. Together with their high conductivity, matching energy levels with the work function of carbon electrodes, and excellent environmental stability, this NC displays a cathodic photocurrent density as high as 335 µA cm ‐2 , two orders of magnitude higher than other perovskites in aqueous solutions without the need of other electron acceptors. These combined properties suggest that the Cs 2 PtBr 6 NCs have great potentials in a wide range of photoelectronic and photoelectrochemical sensing applications.