Enriched‐Bromine Surface State for Stable Sky‐Blue Spectrum Perovskite QLEDs With an EQE of 14.6

Halogen vacancies are of great concern in blue‐emitting perovskite quantum‐dot light‐emitting diodes because they affect their efficiency and spectral shift. Here, an enriched‐bromine surface state is realized using a facile strategy that employs a PbBr2 stock solution for anion exchange based on Cd‐doped perovskite quantum dots. It is found that the doped Cd ions are expected to reduce the formation energy of halogen vacancies filled by the external bromine ions, and the excess free bromine ions in solution are enriched in the surface by anchoring with halogen vacancies as sites, accompanied with the shedding of surface long‐chain ligands during the anion exchange process, resulting in a Br‐rich and “neat” surface. Moreover, the surface state exhibits good passivation of the surface defects of the controlled perovskite QDs and simultaneously increases the exciton binding energy, leading to excellent optical properties and stability. Finally, the sky‐blue emitting perovskite quantum‐dot light‐emitting diodes (QLEDs) (490 nm) are conducted with a record external quantum efficiency of 14.6% and current efficiency of 19.9 cd A−1. Meanwhile, the electroluminescence spectra exhibit great stability with negligible shifts under a constant operating voltage from 3 to 7 V. This strategy paves the way for improving the efficiency and stability of perovskite QLEDs. The enriched‐bromine surface state is controlled by employing PbBr2 stock solution for anion‐exchange based on Cd‐doping perovskite quantum dots (QDs), which shows good passivation to the vacancy defects, resulting in boosted optical properties and stability. The stable sky‐blue spectrum quantum‐dot light‐emitting diodes (QLEDs) based on the controlled QDs are conducted with a record EQE of 14.6% and current efficiency (CE) of 19.9 Cd A−1.