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

Metal halide perovskites, such as methylammonium lead halide (CH3NH3PbBr3), have recently attracted tremendous attention due to their outstanding properties and promising applications. Here, CH3NH3PbBr3 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.