Pure Cs<sub>4</sub>PbBr<sub>6</sub>: Highly Luminescent Zero-Dimensional Perovskite Solids

So-called zero-dimensional perovskites, such as Cs<sub>4</sub>PbBr<sub>6</sub>, promise outstanding emissive properties. However, Cs<sub>4</sub>PbBr<sub>6</sub> 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 Cs<sub>4</sub>PbBr<sub>6</sub> with remarkable emission properties. We found that pure Cs<sub>4</sub>PbBr<sub>6</sub> in solid form exhibits a 45% photoluminescence quantum yield (PLQY), in contrast to its three-dimensional counterpart, CsPbBr<sub>3</sub>, which exhibits more than 2 orders of magnitude lower PLQY. Such a PLQY of Cs<sub>4</sub>PbBr<sub>6</sub> 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 Cs<sub>4</sub>PbBr<sub>6</sub>, 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.