The rare combination of optical transparency and high electronic mobility is found in oxides of a select group of metals (e.g., Zn, In, Sn). Transparent conducting oxides (TCOs) serve as transparent electrodes in a wide range of applications, from flat panel displays to solar cells. More recently, their semiconducting analogues, transparent oxide semiconductors (TOSs) are being employed as active elements in flexible and transparent thin film transistors. In both cases, we investigate their underlying defect chemistry and how this governs transparent semiconductivity and conductivity. An exciting new area of research involves amorphous forms of TCO and TOS materials.  Our recently launched DOE-EFRC programs are investigating structure-property relationships in amorphous n-type TCOs and crystalline p-type TCOs for organic and inorganic solar cells, respectively.

High ionic conductivity is required for advanced electrochemical systems, e.g., batteries and fuel cells. We are investigating the role of nanocrystallinity in the transport properties of “nano-ionics” as electrolytes for such applications. In particular, owing to enhanced grain boundary transport, nano-ionics may enable lower operating temperatures than currently available with state-of-the-art solid oxide fuel cells (SOFCs). MIECs combine both ionic and electronic conductivity and are often used as SOFC electrodes. Our research addresses the role of grain boundaries in the transport properties of both nano-MIEC and nano-ionic materials.

Our group is developing models and methods for characterizing the grain core vs. grain boundary properties of nanoceramics. We employ AC-impedance spectroscopy (AC-IS) and our newly developed “nano-Grain Composite Model” to separate local electrical/dielectric properties of technologically important electroceramics.