Surface Ligand Engineering for Near-Unity Quantum Yield Inorganic Halide Perovskite QDs and High-Performance QLEDs

Despite the great potential of all-inorganic CsPbX₃ (X = Br or I) quantum dots (QDs) for light-emitting diodes (QLEDs), their emission properties have been impeded by the long insulating ligands on the QD surface. To address the problem, an efficient surface ligand engineering method has been executed by using a short conjugation molecular ligand phenethylamine (PEA) as ligands to synthesize CsPbX₃ QDs and then treating the CsPbX₃ QD films with phenethylammonium bromide (PEABr) or phenethylammonium iodide (PEAI). The results indicate that the short conjugation molecular ligand is successfully adsorbed on the surface of CsPbX₃ QDs to instead long insulating ligands, resulting in the remarkable enhancement of the carrier injection and transport. The incorporation of phenethylamine (PEA) as synthetic ligand causes the fewer trap states in both CsPbBr₃ and CsPbI₃ QDs, exhibiting the near-unity photoluminescence quantum yields (PLQYs) of 93% and 95%, respectively. The luminance of CsPbBr₃ and CsPbI₃ QLEDs could be improved to 21470 and 1444 cd m^-2, respectively, when the long insulating ligands were further replaced with conjugation molecular ligands. Particularly, the external quantum efficiency (EQE) of CsPbI₃ QLEDs reaches 14.08%, which is among the highest efficiency of red perovskite LEDs.