The synthesis and electronic characterization of nanocrystalline p-type CuGaO₂ has been investigated for its application as a transparent hole transport material in thin film solar cells. CuGaO₂, along with other CuMO₂ materials (M = Al^III, In^III, Cr^III, Sc^III, B^III), is attractive because of its wide band gap and two-dimensional delafossite crystal structure; the latter of which results in a large mobility of valence band holes, an uncommon feature for p-type metal oxides. Research in our group has focused on increasing our understanding of the electronic structure of this nanocrystalline material through physical methods such as electrochemistry and spectroscopy. Through these studies we hope to gain insight on what factors control hole transport and the physical nature of defect states in this class of materials.

The core-shell type nanostructure, which can be broadly defined as an inner nanoparticle (core) encapsulated inside an outer layer material (shell), is one of the simplest but most important motifs in multi-component systems. Here, I will describe the utilization of core-shell synergy for exploring new and complex nanomaterials. Our studies have unveiled the diverse interactions between core and shell: (1) shell can protect the integrity of the core, and retain its surface ligands, which is essential in the following separations, mechanistic studies and other practical applications; (2) shell coverage of the core is controllable through tuning the core-shell interfacial free energy, which breaks the uniformity of surface properties and makes the site-specific coding on core surface feasible; (3) the shell growth is templated on the core nanoparticle, and this in turn reshapes the core nanoparticle via core-shell synergistic effects.  Our current studies have improved our understanding of how these core-shell interactions operate. Eventually, with these knowledge, greater control of nanomaterials can be achieved, in terms of synthesis, processing and application.

Harnessing sunlight as an alternative energy resource continues to stimulate material science research for the design and synthesis of new photonic materials.  Hybrid organic – inorganic materials have been increasingly studied in the material science community in order to create new materials with unique features.  For the past three years, our group has been focusing on the fundamental light harvesting and photophysics of organic liquid crystals, single crystal and thin film perovskites, and gold nanocluster-quantum dot systems.  In this talk, I will highlight each of these projects and how ultrafast transient absorption plays a vital role for developing structure-property relationships with the aim to develop a mechanistic understanding of exciton and electron/hole dynamics. These studies help establish a fundamental understanding of the photophysical processes in new photonic materials to ultimately guide the design of new materials with targeted ultrafast dynamics and optoelectronic properties.