Organic Materials for Photovoltaic Applications

Benjamin Langley (2011). Organic Materials for Photovoltaic Applications PhD Thesis, School of Chemistry & Molecular Biosciences, The University of Queensland.

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Author Benjamin Langley
Thesis Title Organic Materials for Photovoltaic Applications
School, Centre or Institute School of Chemistry & Molecular Biosciences
Institution The University of Queensland
Publication date 2011-08
Thesis type PhD Thesis
Supervisor Prof. Paul Burn
Dr. Shih-Chun Lo
Total pages 151
Total colour pages 17
Total black and white pages 134
Language eng
Subjects 0305 Organic Chemistry
0303 Macromolecular and Materials Chemistry
0306 Physical Chemistry (incl. Structural)
Abstract/Summary The sun offers us an essentially limitless source of energy; every year the Earth receives eight thousand times more energy from the sun than we currently consume. With climate change at the forefront of the global agenda combined with the uncertainty of traditional non-renewable energy sources becoming more uncertain, research into solar power is an essential avenue of investigation. The “traditional” solar cell is based on inorganic semiconductors that are costly to make but provide the best efficiencies. Dye sensitised solar cells (DSSCs) are proving a cost-effective alternative, however the efficiencies of these are low compared to solar cells based on inorganic semiconductors. This thesis concerns the synthesis and characterisation of novel dyes for use in dye sensitised solar cells. They have primarily been designed to include charge-transporting carbazole units in their structure, with the aim of improving the performance of DSSCs by facilitating charge transport across the electrolyte dye photoelectrode interface. A secondary objective was to investigate the effect of modifying the substitution pattern of the common bipyridyl ligands present in most ruthenium(II) dyes used in DSSCs. A series of ruthenium(II) complexes were synthesised via a convergent method, using a number of different surface groups, to investigate the effects of molecular size on the efficiency of these dyes in a DSSC. The dyes were characterised by physical, optical and electrochemical methods and the equilibrium surface coverage of the dye was determined. The solar spectrum weighted light harvesting efficiency for each of the complexes was calculated and used as a guide for the expected solar cell performance of the complexes. Two of the dyes showed improved performance for their calculated light harvesting efficiency, relative to dyes that contain no charge-transporting groups. One of the dyes showed an unusual tendency to aggregate inside the photoelectrode, giving inflated equilibrium surface coverage values. The substitution pattern of the bipyridyl ligands was found to greatly affect the optical properties, where the 5,5’-substituted dyes, when compared to dyes with 4,4’substituted ligands, showed a red shift in the absorption and lower molar absorptivity. This in turn resulted in higher efficiencies for the 4,4-substituted dyes. In order to understand these changes in properties, resonance Raman spectroscopy was performed on three dyes to probe the electronic structure of the optical transitions. Resonance Raman spectroscopy can give this information as bonds that are involved in a particular optical transition shown enhancement of their Raman vibrations when excited with light of the same energy as the transition. This study showed that ruthenium(II) bipyridyl complexes with a 4,4’-substitution pattern have nearly identical resonance Raman spectra at the longest wavelength absorption but the 5,5’-substituted complex is significantly different, indicating a different electronic excitation profile for 5,5’-substituted complexes. Finally, a purely organic dye based on a catechol binding unit and including a 3,6-bis(9,9-di-n-propylfluorenyl)carbazole group was synthesised to investigate the effect of this group on aggregation and recombination. The properties and performance of this dye were not significantly different from the parent dye on which it was based; however an improved dark current response indicates that this is a path that could lead to more improvements with further investigation.
Keyword Dye sensitised solar cells
Ruthenium(II) complexes
Organic Synthesis
Bipyridyl ligands
charge transport
Catechol dyes
Dye surface coverage
Additional Notes 21,26,27,28,71,78,79,86,89,92,95,98,99,100,110,111,114

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Created: Tue, 22 May 2012, 11:54:32 EST by Mr Benjamin Langley on behalf of Library - Information Access Service