Structure and surface properties of size-tuneable CsPbBr₃ nanocrystals

This investigation has characterised the structure and surface chemistry of CsPbBr₃ nanocrystals with controlled diameters between 6.4 to 12.8 nm. The nanocrystals were investigated via a thorough ¹³³Cs solid state NMR and nuclear relaxation study, identifying and mapping radially-increasing nanoscale disorder. This work has formalised ¹³³Cs NMR as a highly sensitive probe of nanocrystal size, which can conveniently analyse nanocrystals in solid forms, as they would be utilised in optoelectronic devices. A combined multinuclear solid state NMR and XPS approach, including ¹³³Cs-¹H heteronuclear correlation 2D (HETCOR) NMR, was utilised to study the nanocrystal surface and ligands, demonstrating that the surface is Cs-Br rich with vacancies passivated by didodecyldimethylammonium bromide (DDAB) ligands. Furthermore, it is shown that a negligible amount of phosphonate ligands remain on the powder nanocrystal surface, despite the key role of octylphosphonic acid (OPA) in controlling the colloidal nanocrystal growth. The CsPbBr₃ NCs were shown to be structurally stable under ambient conditions for up to 6 months, albeit with some particle agglomeration.