Halide-modulated (Cs,NH4)Pb(Br,X)3 (X = Cl, Br, I) perovskite nanocrystals with tunable emissions via cation/anion co-exchanging strategy

All-inorganic halide perovskite nanocrystals (PNCs) have attracted extensive attention due to their potential for the next-generation displays. The ammonium and halide composition affect strongly the photoelectrical properties and the long-term stability of PNCs. In this work, we present a novel class of mixed all-inorganic (Cs,NH 4 )Pb(Br,X) 3 (X = Cl, Br, I) NCs prepared via cation/anion co-exchange reaction between CsPbBr 3 NCs and the mechanochemically reacted NH 4 Pb n X 2n+1 (X = Cl, Br, I, n = 1 or 2) powders. The cubic morphologies of (Cs,NH 4 )Pb(Br,X) 3  NCs with different halogen element combinations were successfully obtained. In the meanwhile, the extended emission ranges from deep-blue (453 nm) to warm-yellow (564 nm). Higher PLQY and higher stability against ambient air and UV light were achieved simultaneously by controlling the ion co-exchanging process. The photoluminescence quantum yield (PLQY) of (Cs,NH 4 )Pb(Br,X) 3 (X = Cl, Br, I) NCs were also significantly enhanced compared with that of pure CsPbBr 3 after ions exchanging (>85% versus 58%). In addition, the stability of (Cs,NH 4 )Pb(Br,X) 3 (X = Cl, Br, I) NC thin films under the UV-irradiation and in the ambient atmosphere were also dramatically improved. The cation/anion co-exchanging synthetic strategy developed in our research provides a new pathway to modulate and realize mixed-ion PNCs with high optoelectronic performance.