Adsorption and charge transfer dynamics of photovoltaic and photocatalytic dye-sensitizers

Weston, Matthew (2014) Adsorption and charge transfer dynamics of photovoltaic and photocatalytic dye-sensitizers. PhD thesis, University of Nottingham.

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In this thesis photovoltaic and photocatalytic water-splitting dye complexes have been studied adsorbed onto the rutile TiO2(110) surface. The photovoltaic dye-sensitizer N3 (cis-bis(isothiocyanato)bis(2,2’-bipyridyl-4,4’-dicarboxylato)-ruthenium(II)) was studied along with Ru 455 (cis-bis(2,2’-bipyridyl)-(2,2’-bipyridyl-4,4’-dicarboxylic acid) ruthenium(II)) and Ru 470 (tris(2,2’-bipyridyl-4,4’-dicarboxylic acid) ruthenium(II)) which have very similar chemical structures. Dipyrrin-based dye complexes PY1 bis(5-(4-carboxyphenyl)-4,6-dipyrrin)bis(dimethylsulfoxide)Ruthenium(II)) and PY2 (bis(5-(4-carboxyphenyl)-4,6-dipyrrin)(2,2’-bipyridine) Ruthenium(II)) were also studied which should have different bonding geometries on the TiO2 surface. A single centre water-splitting dye complex (aqua(2,2’-bipyridyl-4,4’-dicarboxylic acid)-(2,2’:6’,6”-terpyridine) Ruthenium(II)) was studied along with a chloride containing analog ((2,2’-bipyridyl-4,4’-dicarboxylic acid)-(2,2’:6’,6”-terpyridine)chloride Ruthenium(II)). The molecules studied here would have been damaged using traditional UHV deposition techniques so electrospray deposition was used to deposit intact molecules in situ for experiments in UHV.

Adsorption geometries of the molecules on the TiO2 surface were investigated using experimental photoemission data supported by density functional theory (DFT) calculations. Dipyrrin-based dye complexes were found to bond with both available carboxylic acid groups to the TiO2 surface. Also the results suggest that Ru 470 is most likely to bond to the TiO2 surface with a different bonding geometry to other bipyridine-based complexes with very similar chemical structures.

The molecular orbitals of the dye complexes were investigated using near-edge x-ray absorption fine structure spectroscopy (NEXAFS). DFT calculations provided possible spatial distributions of the molecular orbitals involved in charge transfer. Energetic alignments were performed using data from visible light spectroscopy to compare energetics for core and valence-hole excitation.

The core-hole clock implementation of resonant photoemission spectroscopy was used to measure upper limits on the timescale of charge transfer from the excited adsorbate molecules to the TiO2 surface. The results show charge transfer timescales mostly within the low-femtosecond timescale. The Ru 470 complex was found to be relatively slow at charge transfer possibly due to the different bonding geometry it appears to adopt on the TiO2 surface.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: O'Shea, J.N.
Moriarty, P.J.
Subjects: Q Science > QC Physics > QC501 Electricity and magnetism
Faculties/Schools: UK Campuses > Faculty of Science > School of Physics and Astronomy
Item ID: 14258
Depositing User: EP, Services
Date Deposited: 30 Jan 2015 13:28
Last Modified: 14 Sep 2016 02:23

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