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 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 photoexcitation of carriers equivalent to LED current densities of ∼3.5 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. ; J. S. and S.D.S. acknowledge the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (HYPERION, grant agreement number 756962). S.D.S acknowledges funding from the Royal Society and Tata Group (UF150033). R.H.F. and Y.L. acknowledge sup-port from the Simons Foundation (grant 601946). M.A. and D.K. acknowledges funding from the European Union's Hori-zon 2020 research and innovation programme under the Ma-rie Skłodowska-Curie (grant agreement number 841386 and 841136, respectively). K.J. acknowledges funding from the Royal Society (RGFR1180002). K.F. acknowledges a George and Lilian Schiff Studentship, Winton Studentship, the Engineer-ing and Physical Sciences Research Council (EPSRC) student-ship, Cambridge Trust Scholarship, and Robert Gardiner Scholarship. C. P. G. acknowledges the European Research Council (ERC) under the European Union's Horizon 2020 re-search and innovation program (835073) and the Royal Society for a Research Professorship (RP\R1\180147). The authors acknowledge the EPSRC for funding (EP/R023980/1).