Varying the Concentration of Organic Acid and Amine Ligands Allows Tuning between Quantum Dots and Magic-Sized Clusters of CH₃NH₃PbBr₃ Perovskite: Implications for Photonics and Energy Conversion

Abstract

Metal halide perovskites, such as methylammonium lead halide (CH 3 NH 3 PbBr 3 ), have recently attracted tremendous attention due to their outstanding properties and promising applications. Here, CH 3 NH 3 PbBr 3 perovskite magic-sized clusters (PMSCs) and perovskite quantum dots (PQDs) are synthesized by surface passivation with various organic acids and amines through a ligand-assisted reprecipitation process (LARP). Their optical properties are investigated with ultraviolet−visible (UV−vis) absorption and photoluminescence (PL) spectroscopy. The structures and optical properties of the PMSCs and PQDs can be controlled by varying the ligand/precursor ratio and type as well as the concentration of ligands. Specifically, a high ligand/precursor ratio and excessive amines favor PMSCs, whereas excessive acids lead to the generation of PQDs over PMSCs. As a result, we can tune between PQDs and PMSCs by changing the amine/acid ligand ratio. Energy-dispersive X-ray (EDS) elemental mapping confirms the presence of the constituent elements of the perovskite, namely, Pb and Br. With the help of Fourier transform infrared (FTIR) results, a model is proposed to explain the mechanism of formation of both PQDs and PMSCs as well as their interconversion in terms of the ligands passivating the surface defect sites. This study provides important insights into the fundamental growth mechanisms of perovskite nanostructures, especially in terms of the interplay between the perovskite precursors and passivating ligands. The work has significant implications in applications of metal halide perovskites in photonics and energy conversion.

Synergetic effect of the surface ligand and SiO2 driven photoluminescence stabilization of the CH3NH3PbBr3 perovskite magic-sized clusters

“…The perovskite samples were prepared using a ligand assisted reprecipitation (LARP) method as described in previous reports 10 , 26 . Excessive surface ligands comprising oleylamine and oleic acid are used as capping ligands to produce the ultrasmall size of interest 9 , 10 .…”

“…The perovskite samples were prepared using a ligand assisted reprecipitation (LARP) method as described in previous reports 10 , 26 . Excessive surface ligands comprising oleylamine and oleic acid are used as capping ligands to produce the ultrasmall size of interest 9 , 10 . The PL emission of the samples precipitated in room temperature exhibits a blue shift emission from 550 nm up to 450 nm in varying the ligand concentration ratio (Fig.…”

“…The metastability behaviour of PMSCs owing to the abundant charging defects in perovskite surface, including positive-charge defect (i.e., halide ion vacancy) and negative-charge defects (i.e., cation vacancy and PbX 4 2− anti-site defects) 8 . The surface passivation MSCs by various capping ligands, including organic acid and amines have been reported 9 , 10 . It was demonstrated that the PMSCs and PQD structure could be tunning by adjusting the ligand concentration ratio between acid and amines-based ligands implying the crucial role of the ligands to the MSCs formation 9 , 10 .…”

“…The surface passivation MSCs by various capping ligands, including organic acid and amines have been reported 9 , 10 . It was demonstrated that the PMSCs and PQD structure could be tunning by adjusting the ligand concentration ratio between acid and amines-based ligands implying the crucial role of the ligands to the MSCs formation 9 , 10 . Unfortunately, the dynamic nature of the interaction between PMSCs surface and capping ligands permits the ligand detachment from the PMSCs surface under various conditions 11 .…”

“…Unfortunately, the dynamic nature of the interaction between PMSCs surface and capping ligands permits the ligand detachment from the PMSCs surface under various conditions 11 . A sample preparation 9 , including vacuum conditioning 10 , 12 , drying process 13 , or even simple purification steps that alter the samples' ligand concentrations 14 , may disrupt the initial PMCS structure concerning the reliability characterization. The ligand's highly dynamic binding state that strongly correlated to their concentration might result in various complex problems in those sample preparation.…”