Abstract:

Efforts to design crystalline materials with tailored properties often begin with an idealized model of structure and bonding; however, bridging the gap from models to comprehensive structure–property relationships relies on an appreciation of the imperfections and reactivity of real materials. Moreover, materials are increasingly combined in complex device architectures that feature nuances at solid interfaces—features that often elude conventional characterization and compositional optimization approaches. In this talk, I will present case studies at the intersection of defect chemistry and semiconductor physics, order–disorder relationships in materials chemistry, and emerging characterization methods tailored to study nanoscale heterogeneity. The lessons we draw from these studies are particularly important in the development of advanced materials aimed at (i) efficiently storing or converting energy and (ii) expanding the utility of next-generation devices for energy and electronics. Indeed, cohesion between materials chemistry and structure–property engineering will be required to reach ambitious energy efficiency targets in technologies for a decarbonized society.

First, I contend that the remarkable yet fragile behavior of halide-perovskite solar absorbers stems from their intrinsic disorder and defect chemistry. These features shape their electronic structure, stability, and integration into optoelectronic devices. Our analysis of equilibrium thermodynamics and related transport kinetics in single crystals reveals a pervasive point-defect reaction that couples ionic conductivity and electronic doping. Thus, we reconcile many characteristic instabilities and identify strategies to realize stable composition and electronic properties in the large family of halide-perovskite semiconductors. Recent work extends our understanding of this defect chemistry to the stability of state-of-the-art solar absorbers and heterogeneous solid transformations. Second, I will present ongoing work using advanced electron microscopy and diffraction techniques to examine the structure of complex intercalation compounds. Intercalation is a foundational chemical transformation in energy storage and functionalization of two-dimensional (2D) materials, yet mechanistic details and the extent of chemical–mechanical coupling remain difficult to evaluate. Our investigation of 2D semiconductors as hosts for single-molecule magnets provides (i) a new approach in quantum information science and (ii) perspectives on methods to characterize local (dis)order in hybrid materials.

Biography:

Julian Vigil is a Schmidt Science Fellow at the University of California, Berkeley, appointed in the College of Chemistry with Prof. Jeffrey R. Long and at the National Center for Electron Microscopy (Lawrence Berkeley National Laboratory) with Prof. Andrew M. Minor. His work combines the synthesis of novel materials with the development of applied crystallography techniques—including X-ray scattering and nanoprobe electron diffraction—to investigate nanoscale heterogeneity and structure–property relationships. Julian completed his Ph.D. in chemical engineering at Stanford University as a National Science Foundation Graduate Research Fellow and Stanford Graduate Fellow under the supervision of Profs. Hemamala I. Karunadasa and Michael F. Toney, where he studied defect chemistry, structure–property–processing relations, and magnetism in halide-perovskite semiconductors. In prior training, Julian earned an M.Phil. in chemistry from the University of Cambridge as a Churchill Scholar and a B.S. in chemical engineering from the University of New Mexico as a Regents’ Scholar.