The Benefit and Challenges of Zero-Dimensional Perovskites.

To break free of the limitations imposed by three-dimensional (3D) perovskites, such as their lackluster stability, researchers have opened new frontiers into lower-dimensional perovskite derivatives. Thanks to advances in solvent-based synthesis methods, zero-dimensional (0D) inorganic perovskites, mainly Cs4PbBr6, have recently reemerged in various forms (from single crystals to nanocrystals) as materials with properties that bridge organic molecules and inorganic semiconductors. These properties include intrinsic Pb2+ ion emission, large exciton binding energy, and small polaron formation upon photoexcitation, in addition to anomalous green photoluminescence with improved stability and high quantum yield. Moreover, the demonstration of Cs4PbBr6-based light-emitting diode (LED) devices highlights the accelerating efforts toward their applications and motivates further investigations of these emerging materials. This Perspective summarizes the progress in the field of Cs4PbBr6 perovskites, focusing on their molecular-electronic properties and hotly debated green photoluminescence. We conclude by presenting the implications of the unique findings and suggesting opportunities for the future development and applications of these 0D perovskites.