Chloride Vapor Annealing for Efficient Deep-Blue Perovskite Light-Emitting Diodes

Achieving deep-blue emission is crucial for the practical application of perovskite light-emitting diodes (LEDs) in displays. Increasing the ratio of chlorine to bromine in the perovskite is a facile method to achieve deep-blue emission. However, the low solubility of chloride in the perovskite precursor solution and the low formation energy of defects present challenges that limit device efficiency. Here, we demonstrate a chloride vapor annealing method utilizing ethylammonium chloride (EAC) to enable in situ halide exchange and defect passivation. We find that the chloride ions from EAC can effectively exchange with the bromide ions in the perovskite, resulting in blue-shifted emission. Additionally, the ammonium group in EAC can coordinate with unsaturated lead, reducing trap-assisted nonradiative recombination. Based on this approach, we achieve efficient deep-blue perovskite LEDs with a peak external quantum efficiency of 6.8% and color coordinates of (0.131, 0.044), which fully meet the Rec. 2020 blue standard.