Dr. Patrick Woodward
Ohio State University
Department of Chemistry and Biochemistry
Friday, March 17, 2022
Room 120 – Meyerhoff Chemistry Building
Host: Dr. Joe Bennett
“Explorations of halide perovskites – The search for new rare-earth free phosphors and ferroelectrics”
In this talk I will discuss the synthesis, structures, and physical properties of some materials in the halide perovskite family. In the first half of the talk, I will discuss the optical properties of inorganic, lead-free compositions like Cs2AgBiBr6 and Cs2NaBiCl6. Many of these compounds are wide band gap semiconductors and insulators that are not suitable for use as solar absorbers in photovoltaic cells, but with appropriate doping they can exhibit strong photoluminescence that is promising for use in solid state lighting and other applications. Although rare-earth elements can be incorporated, our focus has been on the development of inexpensive solution processable phosphors that do not contain rare earth ions.
In the second half of the talk, I will discuss our studies of hybrid organic-inorganic layered perovskites, with a specific emphasis on understanding structural distortions and using that knowledge to design new polar materials and dielectric materials. Using the tools of group theory, we have mapped out the symmetry consequences of structural distortions in this class of materials. These distortions include octahedral tilting, cation ordering within the inorganic layers, and orientational ordering of the organic cations. The combined analysis shows that certain modes of octahedral tilting are strongly favored in large part because they lead to favorable hydrogen bonding interactions between the halide ions of the inorganic layers and organic cations that sit between the layers. This information is used to guide our search for new lead-free ferroelectrics and multiferroics.