Stable Hexylphosphonate-Capped Blue-Emitting Quantum-Confined CsPbBr₃ Nanoplatelets.

Abstract

Quantum-confined CsPbBr3 nanoplatelets (NPLs) are extremely promising for use in low-cost blue light-emitting diodes but their tendency to coalesce in both solu-tion and film form, particularly under operating device condi-tions with injected charge-carriers, is hindering their adop-tion. We show that employing a short hexyl-phosphonate lig-and (C6H15O3P) in a heat-up colloidal approach for pure, blue-emitting quantum-confined CsPbBr3 NPLs significantly sup-presses these coalescence phenomena compared to particles capped with the typical oleyammonium ligands. The phosphonate passivated NPL thin films exhibit photolumines-cence 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 lig-and.