Professor Thomas Hamann, Michigan State University.  Molecular and Material Approaches for Solar Energy Conversion and Storage."  Harvard/MIT Inorganic Chemistry Seminar.

ABSTRACT

This talk will describe our efforts to understand and control the processes determining the efficiency of solar energy conversion systems. One particularly interesting system is the dye-sensitized solar cell, DSSC, where the performance depends on the interplay of various electron-transfer reactions between molecular chromophores, mesoporous metal oxide photoelectrodes and redox shuttles dissolved in solution. The implementation of new redox shuttles is the key to improve the performance. A series of cobalt redox shuttles will be introduced and their behavior as both donor and acceptor in DSSCs will be interpreted in terms of Marcus theory. The results point to redox shuttle design rules for next generation DSSCs. Hematite (α-Fe₂O₃) thin films comprise another system of interest for photoelectrochemical (PEC) water splitting due to its unique combination of suitable optical and electrochemical properties combined with excellent stability and elemental abundance. We have utilized PEC and impedance spectroscopy measurements to show the accumulation of holes in surface states of hematite, which can recombine with conduction band electrons, controls the water oxidation onset potential and thus water splitting efficiency. The results of recent operando infrared spectroscopy measurements which elucidates the nature of these surface accumulated holes and helps establish the mechanism of PEC water oxidation on hematite – or any metal oxide semiconductor surface – will also be presented.