Friday, August 23, 2013
Joint Center For Artificial Photosynthesis Seminar
Silicon-based Metal-Insulator-Semiconductor Photoelectrodes as a Platform for Highly Efficient Solar Water Splitting
Dr. Daniel Esposito, NRC Postdoctoral Fellow, MML Thin Film and Nanostructure Processing Group, National Institute of Standards and Technology (NIST)
Solar-driven water splitting with photoelectrochemical (PEC) cells is an attractive pathway for renewable production of hydrogen (H2), but the efficiency and stability of semiconducting photoelectrodes must be improved to make this technology economically viable. One promising approach to achieving both high efficiency and good stability is the metal-insulator-semiconductor (MIS) photoelectrode design. This MIS architecture consists of catalytic metal structures, or collectors, deposited on an oxide-covered semiconductor. Of great importance to this design is the insulating oxide layer, which must simultaneously protect the semiconductor from the potentially corrosive electrolyte while mediating tunneling of electrons between the semiconductor and collectors. Silicon is a commonly used photovoltaic (PV) material that is attractive for use in MIS photoelectrodes, but the efficiencies of Si-based MIS photoelectrodes used for water splitting lag far behind those demonstrated by Si-based photovoltaic cells.
In this seminar, I will describe a systematic approach to improving the performance of Si-based MIS photocathodes that is based on studying well-defined arrays of MIS structures with in-situ scanning probe techniques. Specifically, scanning photocurrent microscopy and scanning electrochemical microscopy have been combined to simultaneously record images of quantum efficiency and catalytic activity on MIS photocathodes with high spatial resolution. I will show how this powerful combination of techniques can be used as a diagnostic tool, for screening MIS geometries, and elucidating complex interfacial charge transfer phenomenon such as long-distance carrier collection through inversion layers and a hydrogen-spillover assisted H2 evolution. I will also discuss several other aspects of this research project, including the extension of the MIS architecture to 3D structures, interfacial engineering in MIS junctions, and integration of MIS photocathodes into stand-alone water splitting devices.