(5q) Electrochemically Induced Charge Transfer to Wide Band Gap Semiconductors and Its Implication to Nanowire Based Solar Cells

High quality diamond is an extremely good insulator with a band gap of 5.5 eV. However, for undoped, hydrogen-terminated diamond exposed to air, a p-type conductive surface layer appears that is mediated by adsorbates from the ambient atmosphere. In our recent work we showed that this observed conductivity is due to the charge transfer induced by an electrochemical reaction occurring in adsorbed water film on the surface[1]. The electron transfer depends on the band edge positions of the semiconductor with respect to the redox reactions and affects both its electronic and optical properties.

Although these effects were first observed at diamond/water interphase, they can ocuur other wide band gap semiconductors such as those used in photoelectrochemical cells (PEC). In PEC cells, the photocatalytic activity is strongly influenced by the surface electronic properties of the semiconductor. These properties in turn depend on the nature of defect states and band edge positions of the semiconductor with respect to the redox couple. Thus by controlling these properties one can tailor the performance of photoelectrodes. Nanowire based electrodes in this regard show huge promise because of their surface area. Furthermore, they offer a unique platform for designing hybrid architectures.

The proposed research would be focused on dye sensitized solar cells and photolysis of water. Several different strategies will be adopted for designing novel photoelectrodes that are stable against photocorrosion and can efficiently harvest solar light. Specifically, they are: 1. band gap reduction of oxide semiconductors, 2. protective coatings for existing visible light absorbers against photocorrosion based on the band edge engineering concepts. The studies will couple synthesis and characterization of inorganic nanowires with fundamental studies of energy absorption and transport, for high performance energy conversion device.

[1]. V. Chakrapani, J.C. Angus, A.B. Anderson, S.D. Wolter, B.R. Stoner and G. Sumanasekera, Science 318, 1424 (2007)