Disentangling the Luminescent Mechanism of Cs₄PbBr₆ Single Crystals from an Ultrafast Dynamics Perspective

New all-inorganic perovskites like Cs₄PbBr₆ provide rich luminescent tools and particularly novel physical insights, including their zero-dimensional structure and controversial emitting mechanism. The ensuing debate over the origin of the luminescence of Cs₄PbBr₆ inspired us to tackle the issue through fabricating high-quality Cs₄PbBr₆ single crystals and employing ultrafast dynamics study. Upon photoexcitation, Cs₄PbBr₆ underwent dynamics steps distinct from that of CsPbBr₃, including exciton migration to the defect level on a time scale of several hundred femtoseconds, exciton relaxation within the defect states on the picosecond time scale, and exciton recombination from the subnanosecond to nanosecond time scale. The observation disclosed that crystal defects of Cs₄PbBr₆ induced green emission while CsPbBr₃ mainly relied on quantum confinement to emit at room temperature. The study provides an in-depth understanding of the photoinduced multistep dynamics steps of Cs₄PbBr₆ associated with display and photovoltaic applications, establishing Cs₄PbBr₆ as a new candidate for uses associated with the perovskite family of materials.