Core@Shell AgBr@CsPbBr₃ Nanocrystals as Precursors to Hollow Lead Halide Perovskite Nanocubes

We report the synthesis of colloidal core@shell AgBr@CsPbBr₃ nanocubes by a one-pot approach, where the nucleation and growth of AgBr nanocrystals occurs rapidly after the injection of chemical precursors. This is immediately followed by the overgrowth of CsPbBr₃, delivering AgBr@CsPbBr₃ nanocubes of several tens of nanometers in size, with the volume of the AgBr core being only a small fraction of the overall nanocrystal volume. The formation of a core@shell geometry is facilitated by the epitaxial compatibility between AgBr and CsPbBr₃ along multiple crystallographic directions. Exchange with Cl^- ions leads to Ag@CsPbCl₃ nanocubes, whereas exchange with I^- ions leads to hollow CsPbI₃ nanocubes, due to selective etching of the AgBr (or Ag) core region by the I^- ions diffusing in the nanocubes. These hollow CsPbI₃ nanocubes can then be converted into hollow CsPbBr₃ and CsPbCl₃ nanocubes by halide exchange. The optical emission properties of the hollow CsPbX₃ (X = Cl, Br, I) nanocubes are in line with those expected from large, non-hollow halide perovskite nanocrystals, indicating that the small hollow region in the cubes has no major influence on their optical properties.