Tuning between Methylammonium Lead Bromide Perovskite Magic-Sized Clusters and Quantum Dots through Ligand Assisted Reprecipitation at Elevated Temperatures

Methylammonium lead bromide perovskite magic-sized clusters and quantum dots were synthesized using a new heated ligand assisted reprecipitation (HLARP) technique using organic amines and acids as capping ligands. The optical properties of these nanoparticles were analyzed using UV–vis electronic absorption and photoluminescent spectroscopy. Varying the temperature of the precursor solution while keeping the antisolvent temperature consistent allows for tuning between perovskite magic-sized clusters (MSCs) and quantum dots (PQDs) without the need to use excessive concentrations of capping ligand. Higher precursor solution temperatures favor MSCs, while lower temperatures favor PQDs. Furthermore, increasing the temperature of the system shifts the original emission band from 436 to 453 nm, by increasing the size and potentially through the introduction of surface defects. Low frequency Raman spectroscopy reveals that MSCs have vibrational frequencies that are similar to those of bulk perovskite. Electrospray mass spectrometry and infrared spectroscopy were used to probe the ligands on the surface of the MSCs, indicating that amine is the primary capping ligand and the surface is presumably cation rich.