Changes in photoluminescence (PL) peak width and quantum yield (PLQY) with halide composition were compared for CsPb(Br1-x I x )3 nanocrystals (NCs) prepared by hot-injection and ion-exchange methods. The hot-injection method produced single-phase cubic CsPb(Br1-x I x )3 NCs for each iodide ratio. In contrast, a small amount of orthorhombic phase was observed at higher x for NCs prepared by the ion-exchange methods. The PL peak width of mixed-halide NCs at x = 0.55 was broader than those of CsPbBr3 and CsPbI3, possibly as a result of compositional inhomogeneity among the individual NCs. However, the maximum PL peak width occurred at larger x for the ion-exchange methods, possibly because of partial transition to orthorhombic phase from cubic phase for CsPb(Br1-x I x )3 NCs. The minimum PLQY for the hot-injection method was 25.0% at x = 0.50, which was lower than the PLQYs of CsPbBr3 and CsPbI3 NCs (∼70%). In contrast, the minimum PLQY for the ion-exchange methods occurred at x = ∼0.3. Furthermore, the minimum PLQY was ∼10%, which was lower than 25.0% for the hot-injection method. The addition of halide solution for ion exchange might affect the adsorption state of surface modifiers, leading to the decreased PLQY.
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