Speaker: Prof. Jin Zhong Zhang ,University of California, Santa Cruz
Time: 10:00, September 3, 2019
Venue: Room 502, Building of State Key Laboratory of Luminescent Materials and Devices, Wushan Campus.
Abstract: Organo-metal halide perovskites (OMHP), such as CH3NH3PbI3, and all inorganic metal halide perovskites (IMHPs) exhibit novel electronic, optical and magnetic properties that are promising for various applications including photovoltaics, LED, sensing, and quantum information technology. However, instability due to factors such as UV light, water, oxygen, and temperature limits their applications. The surface of the perovskites strongly affects stability, especially in terms of environmental factors such as solvent and oxygen. 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. Another important finding is that ammonium ions (-NH3+) and carboxylate groups (-COO-) have synergistic effects in surface passivation, attributed to simultaneous passivation of both anions (X-) and cations (Pb2+ or CH3NH3+) on the surface. This is supported by our demonstration that bifunctional peptide-like molecules are highly effective as bidentate ligands for surface passivation. 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. This 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.
Very recently, we have found a simple strategy to synthesize and stabilize magic sized clusters (MSCs) of both OMHP and IMHP that exhibit interesting optical properties potential important for use as unique quantum materials for data storage and single photon emitting applications. In all, our studies demonstrate that surface chemistry approaches are promising for stabilizing OMHP or IMHP, leading to generation of MSCs, QDs, and QD solids, which is significant for many emerging applications.
Biography: Jin Z. Zhang received his B.Sc. degree in Chemistry from Fudan University, Shanghai, China, in 1983 and his Ph.D. in physical chemistry from University of Washington, Seattle in 1989. He was a postdoctoral research fellow at University of California Berkeley from 1989 to 1992. In 1992, he joined the faculty at UC Santa Cruz, where he is currently full professor of chemistry and biochemistry. Zhang’s recent research interests focus on design, synthesis, characterization, and exploration of applications of advanced materials including semiconductor, metal, and metal oxide nanomaterials, particularly in the areas of solar energy conversion, solid state lighting, sensing, and biomedical detection/therapy. He has authored over 340 publications and three books. Zhang has been serving as a senior editor for JPC(L) published by ACS since 2004. He is a Fellow of AAAS, APS, and ACS. He is the recipient of the 2014 Richard A. Glenn Award of the ACS Energy and Fuel Division.
