Molecular insights into growth and time evolution of surface states of CsPbBr3 nanoparticles synthesized by scalable room temperature approach

Room temperature ligand-assisted reprecipitation syntheses of CsPbBr3 nanoparticles (NPs) in open air condition and nonpolar solvent are recently emerging as viable strategies for large-scale production of highly emissive NPs. These procedures encounter some of the relevant requirements for industrial perspectives i.e. high-quality materials, low cost, and synthesis scalability. Here, starting from reported protocols, ad hoc mixtures in anhydrous toluene of precursors (Cs2CO3 and PbBr2) and surfactants, as oleyl amine, alkylcarboxylic acid, didodecyl dimethyl ammonium bromide, tetraoctylammonium bromide, octyl phosphonic acid and phosphine oxide, are selected. The careful analysis of NPs morphology, emission properties, reactive species in the mixtures and composition of the ligands bound at NP surface or free in the final colloidal solution allows to tackle still open issues, including achievement of NP monodispersity, high NP production yield and to unveil the mechanisms behind changes of the emission properties in time. NP size dispersion is proved to depend not solely on ligands interaction to NP surface, but also on the bromoplumbates species in situ generated in the reaction mixture at caesium-precursor solution injection. Purification methods are carefully adjusted so as not to reduce the NP production yield, caused by aggregation phenomena induced by displacement of loosely bound ligands. Meanwhile, the residual species, left in in the reaction mixture due to limited purification, are demonstrated to effectively contribute over time to the fate of the NP properties. Emission is exploited as effective macroscopic evidence of the NPs molecular and structural modifications. In fact, the emission properties, which could be, in principle, predicted on the basis of the ligand density and binding energy, on long time scales are found to evolve in time due to reaction of the residual molecules with the adsorbed ligands.