Metal halide perovskites exhibit
small exciton binding energy,
which leads to a low electron–hole capture rate for radiative
recombination and accordingly decreases the luminescence efficiency.
Reducing the thickness of the perovskite film or the size of the perovskite
crystal is found to be an effective method to spatially confine the
electrons and holes to promote the bimolecular radiative recombination.
Here, we fabricate CsPbBr3/Cs4PbBr6 nanocomposites, applicable for light emission diodes, by a simple
self-assembly method. We effectively reduce the critical size of the
CsPbBr3 nanocrystals in the CsPbBr3/Cs4PbBr6 nanocomposites by adding a certain amount of dimethyl
sulfoxide into the perovskite precursor solution. Accordingly, the
photoluminescence quantum yield of the CsPbBr3/Cs4PbBr6 nanocomposites increased from 56 to 91% due to the
quantum size effect. In situ observation of the growth of CsPbBr3/Cs4PbBr6 nanocomposites reveals that
the reduction of the CsPbBr3 crystal size is due to the
change of the chemical reaction speed during the two-step growth process
of the CsPbBr3/Cs4PbBr6 nanocomposites.