Ligand Dependent Growth and Optical Properties of Hybrid Organo-metal Halide Perovskite Magic Sized Clusters

Magic sized clusters (MSCs), small nanoparticles with a single size or narrow size distribution, possess unique chemical and physical properties. CH3NH3PbBr3 perovskite MSCs (PMSCs) were synthesized using butylamine (BTYA) and valeric acid (VA) as well as 3,3-diphenylpropylamine (DPPA) and VA as capping ligands in an excess amount. The PMSCs were characterized using UV-vis and photoluminescence (PL) spectroscopy. For BTYA-VA PMSCs, there is an excitonic absorption peak at 424 nm and PL peak at 434 nm, while the DPPA-VA PMSCs exhibit an absorption peak at 428 nm and PL peak at 451 nm. The size and optical properties of the PMSCs are found to be dependent on the ligands used for passivation. Additionally, in a series dilution of DPPA-VA PMSCs in toluene, it was discovered that different sized perovskite quantum dots (PQDs) can be synthesized with tunable PL emission with peaks ranging between 451 and 525 nm. This phenomenon was not observed for BTYA-VA PMSCs. This contrast indicates the unique interaction between the DPPA ligand and the toluene solvent for the dilution induced PQD formation. These findings provide new insights into the mechanism of growth and stability of PMSCs that are useful for generating and understanding the formation of larger nanostructures such as QDs.