The adsorption and charge-transfer dynamics of model dye-sensitised solar cell surfaces

Mayor, Louise Charlotte (2009) The adsorption and charge-transfer dynamics of model dye-sensitised solar cell surfaces. PhD thesis, University of Nottingham.

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Abstract

In this thesis, the dye molecule cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)-ruthenium(II) (N3) is studied on the rutile TiO2(110) and Au(111) surfaces. The molecules were deposited onto the surfaces using an ultra-high vacuum (UHV) electrospray deposition system. Thermally labile molecules such as N3 cannot be deposited using the typical method of thermal sublimation, so development of this deposition technique was a necessary step for entirely in situ experiments.

The geometric and electronic structure of the samples are characterised using core-level and valence band photoemission spectroscopy, x-ray absorption fine structure spectroscopy, density functional theory, resonant x-ray emission spectroscopy and scanning tunnelling microscopy. These reveal that N3 bonds to TiO2(110) by deprotonation of the carboxyl groups of one bi-isonicotinic acid ligand so that its oxygen atoms bond to titanium atoms of the substrate, and one of the thiocyanate groups bonds via a sulphur atom to an oxygen atom of the substrate. N3 bonds to Au(111) via sulphur atoms with no deprotonation of the carboxylic groups, and at low coverages decorates the Au(111) herringbone reconstruction. For N3 on TiO2, a consideration of the energetics in relation to optical absorption is used to identify the main photoexcitation channel between occupied and unoccupied molecular orbitals in this system, and also to quantify the relative binding energies of core and valence excitons. For N3 on Au(111), the energetics show that the highest occupied molecular orbital overlaps with the Au conduction band.

The transfer of charge between the N3 molecule and the TiO2(110) and Au(111) surfaces was studied using resonant photoemission spectroscopy and resonant x-ray emission spectroscopy. These techniques, combined with knowledge gained about the geometric and electronic structure, are used to determine the locations and electronic levels of N3 from which charge is readily transferred to the substrate. The core-hole clock implementation of resonant photoemission spectroscopy is used to reveal that electron delocalisation from N3 to TiO2(110) occurs within 16 femtoseconds.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: O'Shea, J.N.
Keywords: charge transfer, dssc, dye-sensitized solar cells, Gratzel cell, solar cell, N3, dye molecules, electropspray, ultra-high vacuum electrospray, core-hole clock, photoemission spectroscopy, PES, XPS, NEXAFS, DFT, density functional theory, TiO2, titanium dioxide, rutile, gold
Subjects: T Technology > TK Electrical engineering. Electronics Nuclear engineering
Faculties/Schools: UK Campuses > Faculty of Science > School of Physics and Astronomy
Item ID: 13521
Depositing User: EP, Services
Date Deposited: 19 Aug 2013 07:20
Last Modified: 14 Sep 2016 18:43
URI: http://eprints.nottingham.ac.uk/id/eprint/13521

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