Ligand-Free Nanocrystals of Highly Emissive Cs₄PbBr₆ Perovskite

Abstract

Although\nligands of long carbon chains are very crucial to form\nstable colloidal perovskite nanocrystals (NCs), they create a severe\nbarrier for efficient charge injection or extraction in quantum-dot-based\noptoelectronics, such as light emitting diode or solar cell. Here,\nwe report a new approach to preparing ligand-free perovskite NCs of\nCs₄PbBr₆, which retained high photoluminescence quantum yield (44%). Such an\napproach involves a polar solvent (acetonitrile) and two small molecules\n(ammonium acetate and cesium chloride), which replace the organic\nligand and still protect the nanocrystals from dissolution. The successful\nremoval of hydrophobic long ligands was evidenced by Fourier transform\ninfrared spectroscopy, ζ potential analysis, and thermogravimetric\nanalysis. Unlike conventional perovskite NCs that are extremely susceptible\nto polar solvents, the ligand-free Cs₄PbBr₆ NCs\nshow robust resistance to polar solvents. Our ligand-free procedure\nopens many possibilities not only from a material hybridization perspective\nbut also in optimizing charge injection and extraction in semiconductor\nquantum-dot-based optoelectronics applications.