All-inorganic lead halide perovskite nanocrystals (NCs) are potential candidates for fabricating high-performance light-emitting diodes (LEDs) owing to their precisely tunable bandgaps, high photoluminescence (PL) efficiency, and excellent color purities. However, the performance of pure red (630−640 nm) all-inorganic perovskite LEDs is still limited by the halide segregation-induced instability of the electroluminescence (EL) of mixed halide CsPbI 3-x Br x NCs. Herein, we report an effective approach to improving the EL stability of pure red all-inorganic CsPbI 3-x Br x NC-based LEDs via the passivation of potassium bromide on NCs. By adding potassium oleate to the reaction system, we obtained potassium bromide surfacepassivated (KBr-passivated) CsPbI 3-x Br x NCs with pure red PL emission and a photoluminescence quantum yield (PLQY) exceeding 90%. We determine that most potassium ions present on the surface of NCs bind with bromide ions and thus demonstrate that potassium bromide surface passivation of NCs can both improve the PL stability and inhibit the halide segregation of NCs. Using KBr-passivated CsPbI 3-x Br x NCs as an emitting layer, we fabricated stable and pure red perovskite LEDs with emission at 637 nm, showing a maximum brightness of 2671 cd m −2 , maximum external quantum efficiency of 3.55%, and good EL stability. The proposed KBrpassivated NC strategy will open a new avenue for fabricating efficient, stable, and tunable pure color perovskite NC LEDs.

Highly luminescent inks are desirable for various applications such as decorative coating, art painting, and anticounterfeiting, to name a few. However, present inks display low photoluminescent efficiency requiring a strong excitation light to make them glow. Here, we report a highly luminescent ink based on the copper-iodide/1-Propyl-1,4-diazabicyclo[2.2.2]octan-1ium (Cu 4 I 6 (pr-ted) 2 ) hybrid cluster with a quantum efficiency exceeding 98%. Under the interaction between the Cu 4 I 6 (pr-ted) 2 hybrid cluster and polyvinylpyrrolidone (PVP), the highly luminescent Cu 4 I 6 (pr-ted) 2 /PVP ink can be facilely prepared via the onepot solution synthesis. The obtained ink exhibits strong green light emission that originates from the efficient phosphorescence of Cu 4 I 6 (pr-ted) 2 nanocrystals. Attractively, the ink displays high conversion efficiency for the ultraviolet light to bright green light emission due to its wide Stokes shift, implying great potential for anticounterfeiting and luminescent solar concentrator coating.

Aggregation-induced emission (AIE) is an attractive phenomenon in which materials display strong luminescence in the aggregated solid states rather than in the conventional dissolved molecular states. However, highly luminescent inks based on AIE are hard to be obtained because of the difficulty in finely controlling the crystallinity of AIE materials at nanoscale. Herein, we report the preparation of highly luminescent inks via oil-in-water microemulsion induced aggregation of Cu-I hybrid clusters based on the highly soluble copper iodide-tris(3-methylphenyl)phosphine (Cu I (P-(m-Tol) ) ) hybrid. Furthermore, we can synthesize a series of AIE inks with different light-emission colors to cover the whole visible spectrum range via a facile ligand exchange processes. The assemblies of Cu-I hybrid clusters with AIE characteristics will pave the way to fabricate low-cost highly luminescent inks.