Post-synthesis phase and shape evolution of CsPbBr3 colloidal nanocrystals: The role of ligands

Abstract

The surface chemistry of colloidal cesium lead bromide (CsPbBr3) nanocrystals is decisive in determine the stability and the final morphology of this class of material, characterized by ionic structure and a high defect tolerance factor. Here, the high sensitivity of purified colloidal nanocubes of CsPbBr3 to diverse environmental condition (solvent dilution, ageing, ligands post synthetic treatment) in ambient atmosphere is proved thanks to a comprehensive morphological (electron microscopy), structural ( /2 XRD and GIWAXS) and spectroscopic investigation. In particular, we establish the ability of aliphatic carboxylic acids and alkyl amines ligands to induce, even in a post preparative process at room temperature, structural, morphological and spectroscopic variations.Upon addition of oleyl amine the highly green emitting CsPbBr3 nanocubes effectively turn into 1D thin tetragonal nanowires or lead halide deficient rhombohedral 0D Cs4PBBr6 structures with a completely loss of fluorescence. On the other hand, addition of oleic acid induces the transformation of nanocubes into still emitting orthorombic 2D nanoplates, with tunable thickness/lateral size,

Low‐Dimensional‐Networked Cesium Lead Halide Perovskites: Properties, Fabrication, and Applications

“…[141,142] If the ligand concentration was too low or too high, the yield and quality of the Cs 4 PbX 6 NCs were poor. In addition, the morphology of resulting Cs 4 PbBr 6 NCs could be tuned, [89,143] for example, Cs 4 PbBr 6 nanowires could be formed from initially cubic CsPbBr 3 NCs, as shown in Figure 10k,l. It is our understanding that amine was not essential in the transformation from CsPbX 3 to Cs 4 PbX 6 , because this transformation was driven by the capability of the ligand to solubilize PbBr 2 , no matter if the ligand was an amine or not.…”

Automated microfluidic screening of ligand interactions during the synthesis of cesium lead bromide nanocrystals

“…However, several studies have suggested that carboxylic acid and carboxylate ligands are in fact present in significant amounts on the surface of CsPbBr 3 nanocrystals, 20,21,23 with the amine and carboxylic acids showing facet-dependent binding. 30 Further, the multiple states and roles of each ligand before, during and after the reaction, 21,65 make this effect hard to disentangle in the context of the current study. However, we note that the effects of ligand branching are evidently not restricted to sterics, but also have implications in the diffusion of ligands in solution, and of ligand stabilized monomers (e.g.…”

“…The acid-base chemistry of a binary aliphatic amine-acid ligand system is critical in determining the morphology and optical properties of cesium lead bromide nanocrystals both during and after synthesis. 22,65 Which ligand species are binding the surface, and by what mechanism, is highly dependent not just on the nature of the surface, but also on the interactions between the ligands and precursors in solution. 20 In our system, by scanning the molar ligand concentration range 0.7 to 1.2 base : acid, we move from a regime of excess acid to excess amine, which should have a distinct effect upon the ratio of the different specifies present (amine versus ammonium, carboxylic acid versus carboxylate).…”

Surface Passivation Strategies for Improving Photoluminescence and Stability of Cesium Lead Halide Perovskite Nanocrystals

“…Upon dilution, an osmatic solvent swelling that arise due to dynamicity between adsorbed and free ligands and the difference in their solubilities in non-polar solvents promote fragmentation that eventually leads to the formation of smaller 2D and 3D nanocrystals. [57] Conversely, the distortion of CsPbBr 3 NCs to zero-phases is driven by the strong binding affinity of Pb 2 + ions to alkyl-amines. [58] Moreover, the formation of nanoplatelets is more favoured in the presence of alkyl carboxylic acids or even bromic acids.…”

“…The post‐synthesis addition of alkyl‐carboxylic acids and alkyl‐amine can induce transformation of CsPbBr 3 nanocubes to 2D nanoplatelets or 1D nanowires and 0D non‐perovskite phases. Upon dilution, an osmatic solvent swelling that arise due to dynamicity between adsorbed and free ligands and the difference in their solubilities in non‐polar solvents promote fragmentation that eventually leads to the formation of smaller 2D and 3D nanocrystals [57] . Conversely, the distortion of CsPbBr 3 NCs to zero‐phases is driven by the strong binding affinity of Pb 2+ ions to alkyl‐amines [58] .…”