March 12
@
1:00 PM
–
2:00 PM
UW-Madison Department of Materials Science and Engineering welcomes Professor Michael F. Toney. His seminar, “Understanding static and dynamic local structure: Metal Halide Perovskites”, will take place on Thursday, March 12 from 1-2 p.m. in MS&E 265.
Bio
Michael Toney is a Professor of Chemical and Biological Engineering and the Materials Science Program at the University of Colorado Boulder. He is a pioneer in the use of X-ray scattering and spectroscopy for the determination of atomic structure in materials for sustainable energy applications, especially inorganic and organic solar cells, interfacial electrochemistry, and electrochemical energy storage. Toney received his B.S. from Caltech and his Ph.D. in physics from the University of Washington. After a NATO Postdoctoral Fellowship in Denmark, he joined the IBM Research Division to focus on the use of X-ray scattering methods for structure determination for polymer thin films and interfaces. He joined the Stanford Synchrotron Radiation Lightsource (SSRL) in 2003 where he initiated science programs in sustainable energy materials. In 2020, he joined CU Boulder. Toney has reviewed several honors including a Fellow of the American Physical Society, the Farrell W Lytle Award and the CU Boulder Deans Performance Award in Research. He is a Thomson Reuters highly cited researchers in Materials Sciences from 2015 – present.
Abstract
Local atomic structure often differs from the global average structure as measured with diffraction and yet the local structure has a profound impact on properties. This structurefunction relationship applies in many materials classes, ranging from organics to Li-ion battery cathodes to oxide and halide perovskites. Accurately characterizing this local structure has proven challenging but recent advances in three-dimensional diffuse scattering (“between” Bragg peaks) has enabled local structure determination. In this talk, I will discuss the importance of local structure and how this can be quantified and will demonstrate this for organicinorganic hybrid halide perovskites [1,2]. These materials are a recently re-invigorated class of semiconductors that have demonstrated very high efficiencies for solar cells after just over a decade of research. While the importance of lattice dynamics and dynamical (dis)order have been recognized in these materials, their nature is only poorly known and understood. We used X-ray and neutron diffuse scattering coupled with molecular dynamics to quantify the nature, size, and time scale associated with dynamical local order in CH NH PbI and CH NH PbBr perovskites. We observe that the nominally cubic perovskite consists of dynamical, twodimensional sheets of lower symmetry tetragonal regions of about 3 nm diameter with several picosecond lifetimes. The implications of the local structure on halide perovskite properties will be discussed.
[1] NJ Weadock et al., Joule 7, 5, 1051-1066 (2023)
[2] DM Ladd, unpublished.