Synthesis of thermally stable and highly luminescent spherical shaped ligand-free Cs ₄ PbBr ₆ nanospheres with a single polar solvent

We demonstrate a simple method to synthesis thermally stable and green luminescent ligand-free Cs ₄ PbBr ₆ nanospheres (NS) with a polar solvent. In this approach, a single polar solvent, N,N-dimethylformamide (DMF) is sufficient enough to convert precursors into cubic shaped ligand-free Cs ₄ PbBr ₆ crystals. Further, the morphology of cubic shaped Cs ₄ PbBr ₆ crystals is reformed into spherical shaped Cs ₄ PbBr ₆ NS by prolonged DMF washing (overnight stirring, 15 h). Besides, the reduction in average particle size of spherical shaped Cs ₄ PbBr ₆ NS (~70 nm) to one-fourth to the original size of cubic Cs ₄ PbBr ₆ crystals (~310 nm). The ligand-free spherical shaped Cs ₄ PbBr ₆ NS showed a high photoluminescence quantum yield of 42.5%, which could compete the conventional ligand mediated Cs ₄ PbBr ₆ crystals. Moreover, spherical shaped Cs ₄ PbBr ₆ NS exhibited a high thermal stability even at 200 °C without sacrificing luminescence intensity. Hence, it is foreseen that this approach brings a new strategy to prepare ligand-free Cs ₄ PbBr ₆ NS as a promising material in optoelectronic devices.