Pure Cs₄PbBr₆: Highly Luminescent\nZero-Dimensional Perovskite Solids

Abstract

So-called zero-dimensional perovskites,\nsuch as Cs₄PbBr₆, promise outstanding emissive\nproperties. However, Cs₄PbBr₆ is mostly prepared\nby melting of precursors\nthat usually leads to a coformation of undesired phases. Here, we\nreport a simple low-temperature solution-processed synthesis of pure\nCs₄PbBr₆ with remarkable emission properties.\nWe found that pure Cs₄PbBr₆ in solid form exhibits\na 45% photoluminescence quantum yield (PLQY), in contrast to its three-dimensional\ncounterpart, CsPbBr₃, which exhibits more than 2 orders\nof magnitude lower PLQY. Such a PLQY of Cs₄PbBr₆ is significantly higher than that of other solid forms of lower-dimensional\nmetal halide perovskite derivatives and perovskite nanocrystals. We\nattribute this dramatic increase in PL to the high exciton binding\nenergy, which we estimate to be ∼353 meV, likely induced by\nthe unique Bergerhoff–Schmitz–Dumont-type crystal structure\nof Cs₄PbBr₆, in which metal-halide-comprised\noctahedra are spatially confined. Our findings bring this class of\nperovskite derivatives to the forefront of color-converting and light-emitting\napplications.