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

We report the synthesis of colloidal core@shell AgBr@CsPbBr 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 CsPbBr, delivering AgBr@CsPbBr 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 CsPbBr along multiple crystallographic directions. Exchange with Cl ions leads to Ag@CsPbCl nanocubes, whereas exchange with I ions leads to hollow CsPbI nanocubes, due to selective etching of the AgBr (or Ag) core region by the I ions diffusing in the nanocubes. These hollow CsPbI nanocubes can then be converted into hollow CsPbBr and CsPbCl nanocubes by halide exchange. The optical emission properties of the hollow CsPbX (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.