Ligand-Free Nanocrystals of Highly Emissive Cs₄PbBr₆ Perovskite

Although ligands of long carbon chains are very crucial to form stable colloidal perovskite nanocrystals (NCs), they create a severe barrier for efficient charge injection or extraction in quantum-dot-based optoelectronics, such as light emitting diode or solar cell. Here, we report a new approach to preparing ligand-free perovskite NCs of Cs₄PbBr₆, which retained high photoluminescence quantum yield (44%). Such an approach involves a polar solvent (acetonitrile) and two small molecules (ammonium acetate and cesium chloride), which replace the organic ligand and still protect the nanocrystals from dissolution. The successful removal of hydrophobic long ligands was evidenced by Fourier transform infrared spectroscopy, ζ potential analysis, and thermogravimetric analysis. Unlike conventional perovskite NCs that are extremely susceptible to polar solvents, the ligand-free Cs₄PbBr₆ NCs show robust resistance to polar solvents. Our ligand-free procedure opens many possibilities not only from a material hybridization perspective but also in optimizing charge injection and extraction in semiconductor quantum-dot-based optoelectronics applications.