(71c) Synthesis and Novel Properties of Metal Halide Perovskites: From Quantum Dots to Magic Sized Clusters and Molecular Clusters

Metal halide perovskites (MHPs) with ABX₃ structure, such as CH₃NH₃PbI₃ and CsPbBr_3, exhibit novel electronic, optical and magnetic properties that are promising for various applications including photovoltaics, LED, sensing, and quantum information technology. However, instability limits their applications. We have developed different surface passivation strategies to stabilize perovskite quantum dots (PQDs) and bulk films using surface chemistry approaches based on molecular ligands. The detailed molecular structures of the ligands make a major difference in their effectiveness of passivation for PQDs vs bulk films, e.g. steric hindrance between ligand molecules. In addition, we have developed conjugated ligands to improve charge delocalization and transfer/transport, as well as phosphonic ligands that are highly effective for passivation, which is particularly important for creating QD solids important for devices applications. In general, we found a “cocktail” approach using a combination of ligands to be most effective in passivating the multiple surface defects. More recently, we have found a simple strategy to synthesize and stabilize magic sized clusters (MSCs) of MHPs, including doping, that exhibit interesting optical properties potential important for use as unique quantum materials for data storage and single photon emitting applications. In our efforts to understand the growth mechanism of MSCs, we discovered a new species that we call molecular cluster (MCs) that do not contain the A component of the perovskites and can be stabilized in solid form of interest for applications such as blue single photon emitters. In all, our studies demonstrate that surface chemistry approaches are promising for stabilizing MHPs, leading to generation of doped and undoped PQDs, MSCs and MCs, which is significant for many emerging applications.