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 Cs 4 PbBr 6 , 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 Pb 2+ 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 Cs 4 PbBr 6 -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 Cs 4 PbBr 6 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.