Metal halide perovskite nanocrystals (PeNCs) have ionic crystal structures, and their optical properties are greatly affected by polar solvents owing to the formation of cationand anion-defects. Herein, we fabricated low driving voltage and high efficiency NC light emitting devices (LEDs) using gel permeation chromatography (GPC) with nonpolar solvents to remove impurities such as excess ligands and reaction solvents. We confirmed that these impurities may be removed completely via the

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... GPC purification process in contrast to the conventional reprecipitation purification process having two-cycles. In addition, we demonstrated the effect of interfacial engineering between the hole transport layer and PeNC layer using alkyl ammonium salts containing Br anion, i.e., oleylamine bromide (OAm-Br), to passivate both cation-and anion-defects in PeNCs. The LEDs based on PeNCs with GPC purification achieved the maximum external quantum efficiency of 4.3% with OAm-Br layer.