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Fundamental understanding of charge transfer from a Ru-based dye adsorbate to a TiO2(110) surface


EMSL Project ID
25695

Abstract

Ru-based dye-sensitized TiO2 solar cells have attracted significant attention because of their potential use in photovoltaic cells[1,2]. These devices utilize films of optically transparent TiO2 particles, a few nanometers in size, each coated with a monolayer of a Ru-based dye. The films are typically 10 µm in thickness coated on a conductive electrode surface. Such devices are known to harvest 46% of solar energy flux, with over 80% conversion efficiency of incident photons to electrical current and overall light-to-electric energy conversion yield of 12% in diffuse daylight. The high surface area of TiO2 nanoparticles and the ideal spectral characteristics of the Ru-based dye (Ru(4,4'-dicarboxylate-2,2'-bypridine)2-(NCS)2 commonly known as N3) enables an efficient harvesting of light in the solar spectrum. To achieve high solar light-to-electric energy conversion efficiencies, the injection of photo-generated electrons from the excited dye molecules to the TiO2 conduction band has to be sufficiently fast, which requires strong electronic coupling between the adsorbate and TiO2, to compete effectively against loss processes, such as charge redistribution and intramolecular thermalization of excited states. Electron transfer from the dye to TiO2 is facilitated by mixing of the dye's molecular orbitals and the TiO2 conduction band levels, which in turn relates to the adsorption configuration and sites of the dye molecules. The N3 dye possesses two biisonicotinic acid groups which are believed to function of anchoring points for the dye to the surface. The N3 dye has cis- and trans- isomers, with the cis- isomer believed to be more thermodynamically stable than the trans- isomer[2].

Project Details

Project type
Large-Scale EMSL Research
Start Date
2007-05-25
End Date
2008-11-04
Status
Closed

Team

Principal Investigator

Michael Henderson
Institution
Pacific Northwest National Laboratory

Team Members

Ponnusamy Nachimuthu
Institution
Environmental Molecular Sciences Laboratory

Theva Thevuthasan
Institution
Environmental Molecular Sciences Laboratory

Bruce Parkinson
Institution
Colorado State University