Despite offering relatively high conversion efficiencies, dye-sensitised solar cells using liquid electrolytes containing either I-/I3 - redox couple or Co2+/Co3+ redox couple suffer from durability problems, such as electrode corrosion and electrolyte leakage. Replacements for liquid electrolytes have been extensively studied, but the efficiencies of the resulting devices remain low. One of the factors that limit the efficiency is the sensitising dye. Large sized hole-transport material results in poor pore-filling and thus leads to a fast back electron recombination that reduces the effective electron diffusion length to few micrometeres. The optimal TiO2 layer thickness (2 μm) for maximal power conversion in solid-state dye-sensitised solar cell is much smaller than the 6-10 μm layer thickness required for quantitative light absorption by many dye molecules. Thus, dyes that can absorb in both visible and near-IR region with high extinction coefficient are needed. In order to achieve this, novel oligomers and ruthenium (II) complexes are designed, synthesized and studied as sensitisers for both liquid state and solid state dye-sensitised solar cells in this thesis. Series of ‘donor-free’ dyes including oligo(3-hexylthiophene) (oligo-3HT) (Chapter 3) and oligo(4,4-dihexyl-4H-cyclopenta[1,2-b:5,4-b’]dithiophene) (oligo-CPDTs) (Chapter 4) functionalized with cyanoacrylic end groups are easily synthesized using cross-coupling. They were fully characterised through electrochemical, spectroscopic and computational techniques, showing versatile colour-tuning, as well as outstanding absorption coefficients up to 75000 M-1cm-1. Liquid and solid-state DSSCs device performances are studied and discussed in terms of the dye structures. These dyes are effective sensitisers for liquid-state and solid-state dye-sensitised solar cells, although they do not contain a typical donor group, thus open a new strategy of designing dyes in the future. New dyes containing different azo ligands as an additional chromophore moiety to enhance light harvesting of Ru complexes (Chapter 5) have been prepared using a protection/deprotection strategy that allows for convenient purification. The absorption spectrum of the dyes showed an enhanced light harvesting compared to the N719 dye that lacks the azo ligand and electrochemical study also showed properties suitable for application as sensitisers in DSSCs. Following hydrolysis, the complexes were investigated in DSSCs, with performance investigated using I-V measurements. Poor performance was observed and we attribute this as mostly likely due to poor charge injection due to short excited-state lifetime. Although the application of these current dyes in DSSCs is not feasible due to their poor performance, this study allowed us to determine the positions of the HOMO and LUMO orbitals and correlate it to the π-acidity of the dyes.

Dye Sensitized Solar Cells (DSSC) possesses huge potential in solar energy utilisation and immense research has been carried out in order to improve its performance. There are several aspects that affect the solar cell’s performance, such as the photon collection efficiency of the cell, the reflectivity of the semiconductor, the transparency and conductivity of the transparent conductive oxide layer, and the photon-electron conversion efficiency. In this research, a pre-patterned substrate was used as a base to fabricate DSSC for improving the photon collection efficiency of DSSC. The pre-patterned substrate was prepared using maskless dry etching technique, resulting in micro-size features on the substrates and giving a 1% reduction on reflectance. The effect of Aluminium doped ZnO sputtered as the Transparent Conductive Oxide layer (TCO) in comparison with a typical DSSC fabricated on Tin doped Indium Oxide glass (ITO) was also studied. The research was carried out in two parts: substrate texturing of glass fabrication with Al:ZnO deposition, and DSSC cell assembly. The first half was carried out in the nanofabrication laboratory at University of Canterbury, New Zealand, and the second half was in National Nano Device Laboratory, Taiwan. The characteristics of both the substrates and the cells were measured using spectrophotometer with integrating sphere and solar cell simulation system. Decrease in reflectance of the Al:ZnO coated substrate at infrared region from 20% to 10 % was achieved. Due to the high resistivity of Al:ZnO and the problem of incapability in TiO2 coating, DSSC cells fabricated with these substrates have efficiencies around 2%, which is lower than the typical DSSC cells fabricated with ITO glass. Future adjustments on the substrate etching process and the cell assembly are needed for optimizing the results. The relatively high resistivity of Al:ZnO also needs to be lower for better DSSC cell performance.

This thesis describes the synthesis of a novel family of porphyrins fused to anthracenes, together with investigations into their optical and electrochemical properties, as well as exploring their potential for application in dye-sensitised solar cells. Chapter 1 gives an overview of the structure-property relationships of large planar pi- systems for organic electronic applications. Porphyrins are introduced as suitable building blocks for such systems, and approaches for extending the pi-conjugation of these macrocycles are presented. A literature review of porphyrins fused to aromatic units is presented in Chapter 2, with a focus on the influence of structure on the optoelectronic properties of such systems. The chapter concludes with a summary of my previous work on the synthesis of anthracene-fused porphyrins, and the aims of this project are stated. Chapter 3 describes the syntheses of fully and partially fused bis-anthracene porphyrin monomers and dimers. By varying peripheral substituents, it was possible to solve problems of aggregation encountered for these systems. Fusion of anthracene units to a porphyrin core was found to result in systems displaying strong absorption in the near-IR, small HOMO-LUMO gaps, and low oxidation potentials. Chapter 4 explores the synthesis, crystal structure and optoelectronic properties of a porphyrin fused to four anthracenes, revealing this system to exhibit the longest wavelength absorption of any porphyrin monomer. The synthesis of a liquid crystalline tetra-anthracene-fused porphyrin was proposed, and attempts to synthesise the necessary anthracene precursors were undertaken. Chapter 5 describes the molecular design and synthetic pathway to a mono-anthracene fused porphyrin, and its unfused analogue, for use in liquid electrolyte dye-sensitised solar cells. By varying the metal oxide layer or lithium ion concentration of the device, it was possible to achieve incident photon to current conversion efficiency (IPCE) responses at wavelengths beyond 1050 nm. Chapter 6 details the experimental synthetic procedures and characterisation data for all the compounds synthesised during this project.

<p>Dye-sensitised solar cells (DSC) have attracted much attention during the last few years due to their high efficiencies and their potentially low production costs. The technology is based on a thin layer of nano sized, high band gap (3.2 eV) TiO2 film. A Ru containing dye (from hereon called the Ru dye) is chemisorbed onto the TiO2 film. This combination acts as the working electrode. The counter electrode consists of a platinum layer which is the catalyst for the regeneration of the Iodine/Iodide electrolyte. The work that is presented here is focused on the results that were obtained during studies of the performance of the DSC under certain reverse bias conditions. When one cell in the series connection in a module is shaded, the current will pass this cell in reverse bias. In such a case the shaded cell will be subjected to a voltage in the reverse direction coming from the other lit cells in the module. This reverse voltage could permanently modify or damage the cell if it is not properly protected. Although the work is focussed on the chemical stability of the dye, various techniques were employed to determine the physical changes in the cell. It was found that a cell that was subjected to a reverse bias of 2 V for 500 min showed a 58% recovery and a cell that was subjected to 4.5 V reverse bias was irreversibly damaged. The UV-vis spectra showed a blue shift (higher energy), the Raman showed no peak at 1713 cm-1 (which indicates the absence of free carboxylate groups) and the FT-IR showed the disappearance of the NC-S absorption band at 2100 cm-1. The combined conclusion is that the &ndash / NCS ligand has been depleted and replaced with I3- ions. When measuring the impedance, the Nyquist plots showed an increase in the charge transfer resistance at the counter electrode when subjected to a reverse bias potential of 2 V. This is confirmed by the Bode plots. This indicates a partial oxidation of the Pt catalyst on the counter electrode. It can therefore be stated with confidence that the changes in the cell after being subjected to a reverse bias potential of 2 V for 500 min are changes on the -NCS bonds on the Ru dye as well as the Pt in the counter electrode.</p>

<p>Dye-sensitised solar cells (DSC) have attracted much attention during the last few years due to their high efficiencies and their potentially low production costs. The technology is based on a thin layer of nano sized, high band gap (3.2 eV) TiO2 film. A Ru containing dye (from hereon called the Ru dye) is chemisorbed onto the TiO2 film. This combination acts as the working electrode. The counter electrode consists of a platinum layer which is the catalyst for the regeneration of the Iodine/Iodide electrolyte. The work that is presented here is focused on the results that were obtained during studies of the performance of the DSC under certain reverse bias conditions. When one cell in the series connection in a module is shaded, the current will pass this cell in reverse bias. In such a case the shaded cell will be subjected to a voltage in the reverse direction coming from the other lit cells in the module. This reverse voltage could permanently modify or damage the cell if it is not properly protected. Although the work is focussed on the chemical stability of the dye, various techniques were employed to determine the physical changes in the cell. It was found that a cell that was subjected to a reverse bias of 2 V for 500 min showed a 58% recovery and a cell that was subjected to 4.5 V reverse bias was irreversibly damaged. The UV-vis spectra showed a blue shift (higher energy), the Raman showed no peak at 1713 cm-1 (which indicates the absence of free carboxylate groups) and the FT-IR showed the disappearance of the NC-S absorption band at 2100 cm-1. The combined conclusion is that the &ndash / NCS ligand has been depleted and replaced with I3- ions. When measuring the impedance, the Nyquist plots showed an increase in the charge transfer resistance at the counter electrode when subjected to a reverse bias potential of 2 V. This is confirmed by the Bode plots. This indicates a partial oxidation of the Pt catalyst on the counter electrode. It can therefore be stated with confidence that the changes in the cell after being subjected to a reverse bias potential of 2 V for 500 min are changes on the -NCS bonds on the Ru dye as well as the Pt in the counter electrode.</p>

Philosophiae Doctor - PhD / Dye-sensitised solar cells (DSC) have attracted much attention during the last few years due to their high efficiencies and their potentially low production costs. The technology is based on a thin layer of nano sized, high band gap (3.2 eV) TiO2 film. A Ru containing dye (from hereon called the Ru dye) is chemisorbed onto the TiO2 film. This combination acts as the working electrode. The counter electrode consists of a platinum layer which is the catalyst for the regeneration of the Iodine/Iodide electrolyte. The work that is presented here is focused on the results that were obtained during studies of the performance of the DSC under certain reverse bias conditions. When one cell in the series connection in a module is shaded, the current will pass this cell in reverse bias. In such a case the shaded cell will be subjected to a voltage in the reverse direction coming from the other lit cells in the module. This reverse voltage could permanently modify or damage the cell if it is not properly protected. Although the work is focussed on the chemical stability of the dye, various techniques were employed to determine the physical changes in the cell. It was found that a cell that was subjected to a reverse bias of 2 V for 500 min showed a 58% recovery and a cell that was subjected to 4.5 V reverse bias was irreversibly damaged. The UV-vis spectra showed a blue shift (higher energy), the Raman showed no peak at 1713 cm-1 (which indicates the absence of free carboxylate groups) and the FT-IR showed the disappearance of the NC-S absorption band at 2100 cm-1. The combined conclusion is that the - NCS ligand has been depleted and replaced with I3- ions. When measuring the impedance, the Nyquist plots showed an increase in the charge transfer resistance at the counter electrode when subjected to a reverse bias potential of 2 V. This is confirmed by the Bode plots. This indicates a partial oxidation of the Pt catalyst on the counter electrode. It can therefore be stated with confidence that the changes in the cell after being subjected to a reverse bias potential of 2 V for 500 min are changes on the -NCS bonds on the Ru dye as well as the Pt in the counter electrode. / South Africa

A method was developed to access the interior of light-guiding structures in order to exploit the enhanced sensing potential of the highly confined electromagnetic field distributions, located within the core of a waveguide. The work presented in this thesis explores therefore the possibilities of optical waveguide spectroscopy utilising transparent mesoporous thin-film waveguides deposited on top of athin gold layer. These multi-layer assemblies are employed in a prism-coupling attenuated total internal reflection (ATR) configuration. The angular read-out of the reflected light intensity allows label-free detection schemes with high sensitivity to changes of the dielectric environment in the case of the presence of analyte molecules within the probing region. This optical waveguide spectroscopy technique has been used to study the real-timediffusion of Ruthenium 535-bisTBA (N-719) dye into mesoporous nanocrystalline titaniumdioxide films. The porous films were prepared on top of gold substrates and prism coupling was used to create a guided wave in the nanocrystalline film. Dying was carried out by bring the film into contact with a 3 x 10-4 moldm-3 dye solution and using optical waveguide spectroscopy to monitor the change in both the refractive index and theextinction coefficient of the nanoporous layer as dye diffused into the porous network. Dyeuptake in a 1.27 μm film was slow with the refractive index of the film still increasing after 22 hours.

Dye design is one of the most important and challenging areas in dye-sensitised solar cell research. The purpose of the work in this thesis is to synthesise and characterise novel ruthenium(II) and copper(I) dyes that will provide insight into the number of binding groups required and the potential use of chromophoric ligands. A series of four simple Ru(II) dyes have been synthesised with the general formula Ru(4,4’- (R)-bipyridine)2(NCS)2 where R represents CH3 or CO2H. The study investigates the number of acid groups required to successfully bind to TiO2 whilst maintaining efficient charge injection. The series consists of one acid group, two acids, two acids on adjacent bipyridines, and three acids groups. Dye uptake was studied via optical waveguide spectroscopy, providing information on dye diffusion, adsorption and desorption kinetics, and surface coverage. Interestingly, the two acid groups on adjacent ligands suggested poor/slow binding to TiO2 surface and a high degree of dye aggregation in comparison to two acid groups on the same ligand. The dye with three binding groups showed strong adsorption to TiO2 and better dye coverage, resulting in a high efficiency. The complexes were all fully characterised by electrochemistry, photoluminescence, absorption spectroscopy, DFT calculations and solar cell performance testing. To date, there has been limited exploration of copper(I) complexes as potential alternatives to ruthenium(II) sensitisers, with even fewer publications reported for Cu(I) heteroleptic species. The neutral complexes that were synthesised are of the general formula: Cu(4,4’- (R)-6,6’-(CH3)-bipyridine)(β-diketonate) and Cu(4,4’-(R)-6,6’-(CH3)-bipyridine)(dipyrrin) where R represents CH3 or CO2Et. Additional blocking groups on the ligands are introduced to minimise structural change during oxidation or MLCT excitation. Improved stability and reproducibility have been shown for complexes containing the dipyrrin ligand, likely due to better steric constraints and better π-overlap with the bipyridine. There has also been a remarkable improvement in light absorption, from 450 nm to 600 nm. In-situ solar studies have been carried out on the Cu(4,4’-(R)-6,6’-(CH3)-bipyridine)(dipyrrin) series and a 0.41% efficiency has been achieved. Computational studies supports the experimental data in which the main transition appears to be ligand centred (dipyrrin) with a small MLCT contribution.

The arrangement of soft materials through solution processing techniques is a topic of profound importance for next generation solar cells; the resulting morphology has a major influence on construction, performance and lifetime. This thesis investigates the connections between the soft matter physics of colloidal systems and solid state dye sensitised (SSDS) and bulk heterojunction (BHJ) solar cells. A study of aqueous titanium dioxide nanoparticulate suspensions was carried out in order to observe how suspension structure can be controlled by altering the inter-colloid potential via pH-induced electrostatic charging. Measurements were performed at volume fractions between 0.025% and 8.2% with the solution pH set to 3.1, 3.5 or 4.5 before mixing. Suspensions with a volume fraction above 4% formed self-supporting gels regardless of the set pre-mix pH. These gels displayed shear thinning behaviour with a power law exponent of 0.8, a yield stress of 11(1) Pa and rheological response consistent with an aggregated fractal network. At lower volume fractions, suspensions exhibited consolidation interpreted as the collapse of a gel of fractal clusters with a fractal dimension of 2.36. The velocity of the suspension/supernatant interface exhibited delayed sedimentation behaviour, as well as further fractal-based power law scalings with volume fraction. Lower volume fraction suspensions were explored using dynamic light scattering. Limited aggregation of ‘stable’ suspensions was observed when compared to primary aggregate radii measured from electron microscopy images. To connect suspension structure and cell manufacture, the behaviour of more concentrated suspensions was observed during the drying of thin films, a process which forms an essential part of a SSDS solar cell. Lowering the pH of the suspension after mixing from 4 to 3 resulted in an ordering of observed crack domains. An increase in film delamination was also observed. Rates of mass loss during drying followed the expected three phase process, although there was an unexpected increase in rate during the initial phase (where rate is usually constant in time). Dynamic light scattering was found to be a useful but demanding technique for studying cluster formation in titanium dioxide suspensions. A non-linear fitting technique utilising the method of moments was thoroughly explored using computer simulated datasets. The algorithm reduced the systematic error in fitted parameters for moderately polydisperse (0:2 < < 0:4) datasets as compared to the commonly applied linear algorithm. The fitting algorithm was also robust to bad initial estimates of parameters. Finally, test solar cells have been built using blends of titanium dioxide and poly-3-hexylthiophene. Device performance was reduced with blend standing time after mixing but could be improved by remixing the blend before spin coating, implicating a reversible process (e.g. aggregation of titanium dioxide or crystallisation of P3HT) in the loss of performance. Addition of a titanium dioxide hole blocking layer before spin coating reduced cell performance. Combining the above studies and these device designs provides a future platform for continuation of this work in the context of real devices.

With increasing concerns of global warming and the impending exhaustion of fossil fuels attention is being turned to renewable sources of energy. The sun supplies 3 x 1024 J per year to the earth which is around 104 times more energy than what the human race consumes. The world’s energy needs would be satisfied if a mere 0.1% of the planet’s surface was covered with solar cells(< = 10%)1, causing the conversion of solar energy (sunlight) into electricity to represent a very practical renewable source. Past research into solar energy has produced a photovoltaic device, which when coupled with highly coloured coordination compounds, enables this conversion. This device is known as a dye-sensitised solar cell (DSSC). Further research has been conducted into the properties of the dyes, and has shown that highly coloured coordination compounds are able to convert solar energy into electrical energy with the highest efficiencies. The dominant compounds in this area to date have been Grätzel’s ruthenium complexes and porphyrins. However, there exists a class of smaller compounds called dipyrrins, described most simply as “half a porphyrin”, which possess many of the attractive qualities for DSSC dyes. Although there are no examples of ruthenium-dipyrrin complexes in the literature, the combination of advantageous properties from both components represent very attractive synthetic targets with huge potential as dyes for DSSCs. The objectives of this thesis were firstly to develop a series of dipyrrin complexes which would be suitable as dyes for DSSCs; then to fully characterise the complexes and investigate the spectroscopic properties of each complex; and finally to determine the suitability of the complexes as dyes for DSSCs. These objectives were fully met, resulting in a set of generic target compounds characterised via 1H NMR, 13C NMR, mass spectrometry (ESI-MS), elemental analysis, and x-ray crystallography. From analyses of the UV-visible, fluorescence, emission, and Raman spectra; and electrochemistry results; the complexes were concluded to be suitable as dyes for DSSC’s. An additional bonus is that the syntheses for these complexes are applicable to any dipyrrin, thus aiding future studies into the use of dipyrrins as dyes for DSSC’s. This thesis summarises the findings of the above outlined research project.