Stable Hexylphosphonate-Capped Blue Emitting Quantum-Confined CsPbBr3 NanoPlatelets

Quantum-confined CsPbBr₃ nanoplatelets (NPLs) are extremely promising for use in low-cost blue light-emitting diodes but their tendency to coalesce in both solution and film form, particularly under operating device conditions with injected charge-carriers, is hindering their adoption. We show that employing a short hexyl-phosphonate ligand (C₆H₁₅O₃P) in a heat-up colloidal approach for pure, blue-emitting quantum-confined CsPbBr₃ NPLs significantly suppresses these coalescence phenomena compared to particles capped with the typical oleyammonium ligands. The phosphonate-passivated NPL thin films exhibit photoluminescence quantum yields of ~40% at 450 nm with exceptional ambient and thermal stability. The color purity is preserved even under continuous photo-excitation of carriers equivalent to LED current densities of ~3 A/cm². ¹³C, ¹³³Cs and ³¹P solid-state MAS NMR reveal the presence of phosphonate on the surface. Density functional theory calculations suggest that the enhanced stability is due to the stronger binding affinity of the phosphonate ligand compared to the ammonium ligand.