Ligand Engineering to Improve the Luminance Efficiency of CsPbBr₃ Nanocrystal Based Light-Emitting Diodes

Abstract

In this paper, we present high-efficiency perovskite light-emitting diodes (PeLEDs) using high-quality green emissive colloidal CsPbBr3 nanocrystals (NCs) of size 11 ± 0.7 nm. The surface chemistry of the NCs was optimized to achieve both reasonably high luminescence and charge transport in NC film. The thickness of the active layer film was controlled by a layer-by-layer deposition technique, where each layer is being deposited and washed using methyl acetate (MeOAc) before we add another layer of NCs. MeOAc being a low surface tension solvent enters into the NC layers and partially removes the long-chain organic ligands oleylamine and oleic acid. The optical and structural properties were measured as a prescreening for these device-grade NCs. Steady-state photoluminescence (PL) and electroluminescence (EL) fwhm (full width at half maxima) are in the range of 20 ± 0.5 nm, suggesting a high color purity feature of these materials suitable for higher color gamut in the display applications. An ITO/PEDOT:PSS/CsPbBr₃–NCs/TPBi/Ca/Al (TPBi is 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)) device structure is fabricated with various thicknesses of the NC layer, and we demonstrated a maximum of ∼5.2 cd/A luminance efficiency for optimal thickness of the CsPbBr₃ NC layer.