This thesis investigates novel hole extraction interfaces and series interconnects for applications in organic photovoltaics, specifically in single junction solid-state dye-sensitized solar cells (DSSCs) and tandem DSSC/polymer bulk heterojunction solar cells. Improvements in hole extraction and device performance by using materials compatible with scalable deposition methods are presented, including tungsten- and molybdenum-disulphide (WS₂ and MoS₂), and p-type doped spiro-OMeTAD (2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene) nanoparticle dispersions. WS₂ and MoS₂ hole extraction layers increase averaged short circuit currents by 20% and 16% respectively, and power conversion efficiencies by 19% and 14% respectively when compared with control devices. Similarly, doped spiro-OMeTAD nano-particle layers improved short circuit current densities by 32% and efficiencies by 9%. Tandem device interconnects using these novel hole extraction formats have been fabricated, but although devices did exhibit rectification, overall performance was poor. Possible reasons for their limited success have been analysed. Dye-sensitized solar mini-modules are also reported. In order to assure the scalability of DSSC technology, these larger area devices were constructed using doctor blade coating to deposit the hole transporter material. As well as achieving a respectable maximum power conversion efficiency of 2.6%, it has also been shown that the extent to which hole transporter infiltrates the mesoporous photoanode of these devices may be tuned by altering substrate temperature during deposition. It was found that an optimal coating temperature of 70 degrees C produced the best efficiency, with a corresponding pore-filling fraction of 41%.

Photovoltaic technologies use light from the sun to create electricity, using a wide range of materials and mechanisms. The generation of clean, renewable energy using this technology must become price competitive with conventional power generation if it is to succeed on a large scale. The field of photovoltaics can be split into many sub-groups, however the overall aim of each is to reduce the cost per watt of the produced electricity. One such solar cell which has potential to reduce the cost significantly is the dye sensitised solar cell (DSC), which utilises cheap materials and processing methods. The reduction in cost of the generated electricity is largely dependent on two parameters. Firstly, the efficiency that the solar cell can convert light into electricity and secondly, the cost to deposit the solar cell. This thesis aims to address both factors, specifically looking at altering the transparent conducting oxide (TCO) and substrate in the solar cell. One method to improve the overall conversion efficiency of the device is to implement the DSC as the top cell in a tandem structure, with a bottom infra-red absorbing solar cell. The top solar cell in such a structure must not needlessly absorb photons which the bottom solar cell can utilise, which can be the case in solar cells utilising standard transparent contacts such as fluorine-doped tin oxide. In this work, transparent conducting oxides with high mobility such as titanium-doped indium oxide (ITiO) have been used to successfully increase the amount of photons through a DSC, available for a bottom infra-red sensitive solar cell such as Cu(In,Ga)Se2 (CIGS). Although electrically and optically of very high quality, the production of DSCs on this material is difficult due to the heat and chemical instability of the film, as well as the poor adhesion of TiO2 on the ITiO surface. Deposition of a interfacial SnO2 layer and a post-deposition annealing treatment in vacuum aided the deposition process, and transparent DSCs of 7.4% have been fabricated. The deposition of a high quality TCO utilising cheap materials is another method to improve the cost/watt ratio. Aluminium-doped zinc oxide (AZO) is a TCO which offers very high optical and electronic quality, whilst avoiding the high cost of indium based TCOs. The chemical and thermal instability of AZO films though present a problem due to the processing steps used in DSC fabrication. Such films etch very easily in slightly acidic environments, and are susceptible to a loss of conductivity upon annealing in air, so some steps have to be taken to fabricate intact devices. In this work, thick layers of SnO2 have been used to reduce the amount of etching on the surface of the film, whilst careful control of the deposition parameters can produce AZO films of high stability. High efficiency devices close to 9% have been fabricated using these stacked layers. Finally, transferring solar cells from rigid to flexible substrates offers cost advantages, since the price of the glass substrate is a significant part of the final cost of the cell. Also, the savings associated with roll to roll deposition of solar cells is large since the production doesn't rely on a batch process, using heavy glass substrates, but a fast, continuous process. This work has explored using the high temperature stable polymer, polyimide, commonly used in CIGS and CdTe solar cells. AZO thin films have been deposited on 7.5um thick polyimide foils, and DSCs of efficiency over 4% have been fabricated on the substrates, using standard processing methods.

Dye-sensitized Solar Cells (DSSC), also known as Grätzel cells, have been identified as a cost-effective, easy-to-manufacture alternative to conventional solar cells. While mimicking natural photosynthesis, they are currently the most efficient third-generation solar technology available. Among others, their cost is dominated by the synthetic dye which consists of efficient Ruthenium based complexes due to their high and wide spectral absorbance. However, the severe toxicity, sophisticated preparation techniques as well as the elevated total cost of the sensitizing dye is of concern. Consequently, the current global trend in the field focuses on the exploitation of alternative organic dyes such as natural dyes which have been studied intensively. The main attractive features of natural dyes are their availability, environmental friendly, less toxicity, less polluting and low in cost. This contribution reports on the possibility of using sepia melanin dye for such DSSC application in replacement of standard costly ruthenium dyes. The sepia melanin polymer has interesting properties such as a considerable spectral absorbance width due to the high degree of conjugation of the molecule. This polymer is capable of absorbing light quantum, both at low and high energies ranging from the infrared to the UV region. The comprehensive literature survey on Grätzel solar cells, its operating principle, as well as its sensitization by natural dyes focusing on sepia melanin has been provided in this master’s dissertation. The obtained results in investigating the morphology, chemical composition, crystalline structure as well as optical properties of sepia melanin samples using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy x-ray diffraction, X-ray Diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), Raman spectroscopy, UV-VIS absorption spectroscopy as well as Photoluminescence (PL) for Grätzel solar cell application have been reported. These results represent an important step forward in defining the structure of melanin. The results clearly show that sepia melanin can be used as natural dye to DSSC sensitization. It is promising for the realization of high cell performance, low-cost production, and non-toxicity. It should be emphasized here that natural dyes from food are better for human health than synthetic dyes. / Physics / 1 online resource (xii, 101 leaves) : illustrations / M. Sc. (Physics)

Dye-sensitized Solar Cells (DSSC), also known as Grätzel cells, have been identified as a cost-effective, easy-to-manufacture alternative to conventional solar cells. While mimicking natural photosynthesis, they are currently the most efficient third-generation solar technology available. Among others, their cost is dominated by the synthetic dye which consists of efficient Ruthenium based complexes due to their high and wide spectral absorbance. However, the severe toxicity, sophisticated preparation techniques as well as the elevated total cost of the sensitizing dye is of concern. Consequently, the current global trend in the field focuses on the exploitation of alternative organic dyes such as natural dyes which have been studied intensively. The main attractive features of natural dyes are their availability, environmental friendly, less toxicity, less polluting and low in cost. This contribution reports on the possibility of using sepia melanin dye for such DSSC application in replacement of standard costly ruthenium dyes. The sepia melanin polymer has interesting properties such as a considerable spectral absorbance width due to the high degree of conjugation of the molecule. This polymer is capable of absorbing light quantum, both at low and high energies ranging from the infrared to the UV region. The comprehensive literature survey on Grätzel solar cells, its operating principle, as well as its sensitization by natural dyes focusing on sepia melanin has been provided in this master’s dissertation. The obtained results in investigating the morphology, chemical composition, crystalline structure as well as optical properties of sepia melanin samples using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy x-ray diffraction, X-ray Diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), Raman spectroscopy, UV-VIS absorption spectroscopy as well as Photoluminescence (PL) for Grätzel solar cell application have been reported. These results represent an important step forward in defining the structure of melanin. The results clearly show that sepia melanin can be used as natural dye to DSSC sensitization. It is promising for the realization of high cell performance, low-cost production, and non-toxicity. It should be emphasized here that natural dyes from food are better for human health than synthetic dyes. / Physics / 1 online resource (xii, 101 leaves) : illustrations / M. Sc. (Physics)

Dye sensitized solar cells (DSSCs) have typically been produced using organic liquids such as acetonitrile as the electrolyte solvent. In real world situations water can permeate into the cell through sealing materials and is also likely to be introduced during the fabrication process. This is a problem as the introduction of water into cells optimized to use an organic solvent tends to be detrimental to cell performance. In this work DSSCs which are optimized to use water as the main electrolyte solvent are produced and characterized. Optimization of aqueous DSSCs resulted in cells with efficiencies up to 3.5% being produced. In terms of characterization, it is generally seen in this work that aqueous DSSCs produce a lower photocurrent but similar photovoltage compared to DSSCs made using acetonitrile and reasons for this are examined in detail. The decreased ability of the aqueous electrolyte to wet the nanoporous TiO2 compared to an acetonitrile electrolyte is found to be a key difficulty and several possible solutions to this problem are examined. By measuring the photocurrent output of aqueous cells as a function of xy position it can be seen that there is some dye dissolution near to the electrolyte filling holes. This is thought to be linked to pH and the effect of 4-tert-butylpyridine and may also decrease the photocurrent. It is found that there is little difference between the two types of cells in terms of the conduction band position and the reaction of electrons in the semiconductor with triiodide in the electrolyte, explaining the similarity in photovoltage. By altering the pH of the electrolyte in an aqueous cell it is found to be possible to change the TiO2 conduction band position in the DSSC. This has a significant effect on the open circuit voltage and short circuit current of the cell, though the pH range available is limited by the fact that dye desorbs at high pH values.

MSc (Physics) / Department of Physics / Titanium dioxide (TiO2) is considered to be an ideal semiconductor for photocatalysis because of its high stability, low cost and safety towards both humans and the environment. Doping TiO2 with different elements has attracted much attention as the most important way of enhancing the visible light absorption, in order to improve the efficiency of the dye sensitized solar cells (DSSCs). In this study, first principle density functional theory was used to investigate electronic and optical properties of bulk anatase TiO2, undoped, and ruthenium (Ru) and strontium (Sr) doped anatase TiO2 (1 0 0) surface. Two different doping approaches i.e., substitutional and adsorption mechanisms were considered in this study. The results showed that absorption band edges of Ru and Sr-doped anatase TiO2 (1 0 0) surface shift to the long wavelength region compared to the bulk anatase TiO2 and undoped anatase TiO2 (1 0 0) surface. Also, the results revealed that the band gap values and the carrier mobility in the valence band, conduction band and impurity energy levels have a synergetic influence on the visible-light absorption and photocatalytic activity of the doped anatase TiO2 (1 0 0) surface. Furthermore, according to the calculated results, we propose the optical transition mechanisms of Ru and Sr-doped anatase TiO2 (1 0 0) surface. Thus, we conclude that the visible light response of TiO2 can be modulated by doping with both Ru and Sr. However, Sr-doped system shows higher photocatalytic activity than the Ru-doped system. The study has successfully probed the interesting optical response mechanism of TiO2 (1 0 0) surface. / NRF

The major contribution of this dissertation is the development of a new integrated measurement and control system for intermixed biogas and photovoltaic systems to achieve safe and optimal energy usage. Literature and field studies show that existing control methods fall short of comprehensive system optimization and fault diagnosis, hence the need to re-look these control methods. The control strategy developed in this dissertation is a considerable enhancement on existing strategies as it incorporates intelligent fuzzy logic algorithms based on C source codes developed on the MPLABX programming environment. Measurements centered on the PIC18F4550 microcontroller were carried out on existing biogas and photovoltaic installations. The designed system was able to accurately predict digester stability, quantify biogas output and carry out biogas fault detection and control. Optimized battery charging and photovoltaic fault detection and control was also successfully implemented. The system optimizes the operation and performance of biogas and photovoltaic energy generation. / Electrical Engineering / M. Tech. (Electrical Engineering)