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

Abstract

Room temperature ligand-assisted reprecipitation syntheses of CsPbBr₃ nanoparticles (NPs) under open air conditions and with non-polar solvents have recently emerged as viable strategies for large-scale production of highly emissive NPs. These procedures must meet 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, such as oleylamine, alkylcarboxylic acid, didodecyldimethylammonium bromide, tetraoctylammonium bromide, octylphosphonic acid and phosphine oxide, are selected. The careful analysis of NP morphology, emission properties, reactive species in the mixtures and composition of the ligands bound at the NP surface or free in the final colloidal solution allows us to tackle still open issues, including the achievement of NP monodispersity, high NP production yield and to unveil the mechanisms behind changes in the emission properties over time. NP size dispersion is proved to depend not solely on ligand interaction with the NP surface, but also on the bromoplumbates species in situ generated in the reaction mixture upon 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 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 over time due to the reaction of the residual molecules with the adsorbed ligands.