Insight into the Ligand-Mediated Synthesis of Colloidal CsPbBr₃ Perovskite Nanocrystals: The Role of Organic Acid, Base, and Cesium Precursors

Abstract

While convenient solution-based procedures have been realized for the synthesis of colloidal perovskite nanocrystals, the impact of surfactant ligands on the shape, size, and surface properties still remains poorly understood, which calls for a more detailed structure-morphology study. Herein we have systematically varied the hydrocarbon chain composition of carboxylic acids and amines to investigate the surface chemistry and the independent impact of acid and amine on the size and shape of perovskite nanocrystals. Solution phase studies on purified nanocrystal samples by (1)H NMR and IR spectroscopies have confirmed the presence of both carboxylate and alkylammonium ligands on surfaces, with the alkylammonium ligand being much more mobile and susceptible to detachment from the nanocrystal surfaces during polar solvent washes. Moreover, the chain length variation of carboxylic acids and amines, ranging from 18 carbons down to two carbons, has shown independent correlation to the size and shape of nanocrystals in addition to the temperature effect. We have additionally demonstrated that employing a more soluble cesium acetate precursor in place of the universally used Cs2CO3 results in enhanced processability without sacrificing optical properties, thus offering a more versatile recipe for perovskite nanocrystal synthesis that allows the use of organic acids and amines bearing chains shorter than eight carbon atoms. Overall our studies have shed light on the influence of ligand chemistry on crystal growth and stabilization of the nanocrystals, which opens the door to functionalizable perovskite nanocrsytals through surface ligand manipulation.

Review—Synthesis, Luminescent Properties, and Stabilities of Cesium Lead Halide Perovskite Nanocrystals

“…12,16,17 The size and shape of the particles are important factors determining the resulting optical properties because of their influence on the bandgap, known as the quantum size effect. 18,19 CsPbX 3 nanocrystals are frequently synthesized in the form of nanocubes, while two-dimensional morphologies such as nanosheets and nanoplatelets are also obtained.…”

“…Pan et al reported the dependence of the particle morphology on the synthesis temperature and the length of the n-alkyl carboxylic acids and n-alkylamines used in the hot-injection method, as summarized in Figure 5. 12 When the synthesis was performed at 170…”

Cesium lead halide ( CsPbX 3, X = Cl , Br, I) perovskite quantum dots-synthesis, properties, and applications: a review of their present status

“…To avoid the solubility-related issues, cesium acetate (CsOAc) was also used as the cesium source. 47 During heating, the formation of a cesium-oleate complex occurs in the flask and this complex is finally converted into CsPbX 3 QDs when it is injected into the source of PbX 2 with OLAM/OLA/1-ODE. It was reported by the authors that the mixture of oleylamine/oleic acid (OLAM/OLA) with 1-ODE helps to solubilize the PbX 2 salt.…”

“…48 The presence of the alkyl ammonium ion on the surface was also confirmed through H 1 NMR spectroscopy. 47 The final morphology of the QDs obtained in the reaction can be varied by simply playing with the addition of new solvents and ligands. Indeed, this solvent chemistry helped to obtain a nanosheets (NSs) structure of Cs-LHQDs, which is normally a complicated one due to its cubic structure.…”

“…53 Also, the different chain lengths of carboxylic acid and alkylamine used in the reaction would also influence the final morphology of the QDs. 47 Other than these, common factors such as temperature and reaction time also influence the morphology of the QDs. For instance, a reaction temperature in the range 140 to 190°C yielded nanocube morphology, whereas the range of temperature of 130 and 90°C leads to the formation of nanoplatelets morphology.…”