Fabrication of blue-emitting CH₃NH₃PbBr₃ nanocrystals: Effects of dipole moment and oxygen functional groups in precipitation solvents on the crystal growth and optical properties of CH₃NH₃PbBr₃ nanocrystals

In this study, blue-emitting CH₃NH₃PbBr₃ nanocrystals (NCs) were achieved by changing the precipitation solvent used in ligand-assisted re-precipitation (LARP) process from a non-polar to a polar solvent. As the dipole moment of precipitation solvent (Sol. B) with oxygen functional groups increased, the photoluminescence (PL) spectrum of CH₃NH₃PbBr₃ NCs was blue-shifted and the crystal size decreased. The high dipole moment of Sol. B increased the interaction between the ligands and Sol. B, promoting the growth of CH₃NH₃PbBr₃ bulk particles rather than CH₃NH₃PbBr₃ NCs. This decreased the monomer concentration in the reaction vessel, thereby limiting the crystal growth of CH₃NH₃PbBr₃ NCs. This study demonstrates that blue-emitting CH₃NH₃PbBr₃ NCs can be achieved by controlling the interaction between the ligands and Sol. B through variations in the dipole moment of Sol. B, and that the presence of oxygen functional groups is essential for tuning the optical bandgap of CH₃NH₃PbBr₃ NCs.