Pure Cs₄PbBr₆: Highly Luminescent Zero-Dimensional Perovskite Solids

So-called zero-dimensional perovskites, such as Cs₄PbBr₆, promise outstanding emissive properties. However, Cs₄PbBr₆ is mostly prepared by melting of precursors that usually leads to a coformation of undesired phases. Here, we report a simple low-temperature solution-processed synthesis of pure Cs₄PbBr₆ with remarkable emission properties. We found that pure Cs₄PbBr₆ in solid form exhibits a 45% photoluminescence quantum yield (PLQY), in contrast to its three-dimensional counterpart, CsPbBr₃, which exhibits more than 2 orders of magnitude lower PLQY. Such a PLQY of Cs₄PbBr₆ is significantly higher than that of other solid forms of lower-dimensional metal halide perovskite derivatives and perovskite nanocrystals. We attribute this dramatic increase in PL to the high exciton binding energy, which we estimate to be ∼353 meV, likely induced by the unique Bergerhoff–Schmitz–Dumont-type crystal structure of Cs₄PbBr₆, in which metal-halide-comprised octahedra are spatially confined. Our findings bring this class of perovskite derivatives to the forefront of color-converting and light-emitting applications.