Thin film solar cells are based on semiconductor materials which are configured together to form a single p-n junction. The p-n junction diode is effectively a simple device that has the capacity to absorb part of the sunlight spectrum and deliver the absorbed photon energy to carriers of electrical current known as electrons and holes. A simple p-n junction solar cell device consists of a p-n junction, a metallic grid and a back contact. The aim of this project was to develop and fabricate a p-n heterojunction diode that is robust, developed with low cost and suitable for large surface area. The device attains a heterojunction configuration, consisting of two thin films, each exhibiting different semiconducting behaviour, namely n-type and p-type semiconductors that are brought together to form a p-n junction diode device. The initial stage of this research was to make and characterise a range of oxide coating compositions that can be sputtered from blends of loosely packed powder targets, using the pulsed DC magnetron sputtering technique. These compositions include fluorine doped tin oxide, antimony doped tin oxide and titanium oxide. The different coatings should be transparent conductive oxides (TCO) that exhibit an n-type semiconductor material characteristic. The second objective was to characterise and develop a p-type semiconductor namely copper aluminium oxide to investigate the optimum compositional ratio and the effect of deposition power on the structure of the thin films. The thin films were characterised in terms of their structural, morphological, optical (transmission and band-gap) and electrical (resistivity, mobility and carrier concentration) conditions. The collection of the charge carriers generated from the incident light was achieved through metal ohmic contacts. This was deposited onto both sides of the device using copper and the silver grids/contacts that are deposited onto the n-type layer and the p-type layers, respectively. The design layout of the grid was optimised in order to increase the device efficiency. The final part of this project was to construct the p-n junction device, test the electrical (current-voltage characteristics) performance and investigate the rectifying behaviour and the formation of the p-n junction.

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This thesis describes some advances of Mathematical Morphology (MM), in order to improve the performance of MM filters in I-D signal processing, . especially in the application to power system protection. MM methodologies are founded on set-theoretic concepts and nonlinear superpositions of signals and images. The morphological operations possess outstanding geometrical properties which make it undoubted that they are efficient image processing methods. However in I-D signal processing, MM filters are not widely employed. To explore the applications of MM for I-D signal processing, our contributions in this area can be summarized in the following two aspects. Firstly, the fram.ework of the traditional signal processing methods is based on the frequency domain representation of the signal and the analysis of the operators' transfer function in the frequency domain. But to the morphological operations, their representations in the frequency domain are uncertain. In order to tackle this problem, this thesis presents our attempt to describe the weighted morphological dilation in the frequency domain. Under certain restrictions to the signal and the structuring element, weighted dilation is transformed to a mathematical expression in the frequency domain. Secondly, although the frequency domain analysis plays an important role in signal processing, the geometrical properties of a signal such as the shape of the signal cannot be ignored. MM is an effective method in dealing with such problems. In this thesis, based on the theory of Morphological Wavelet (MW), three multi-resolution signal decomposition schemes are presented. They are Multiresolution Morphological Top-Hat scheme (MMTH), Multi-resolution Morphov logical Gradient scheme (MMG) and Multi-resolution Noise Tolerant Morphological Gradient scheme (MNTMG). The MMTH scheme shows its significant effect in distinguishing symmetrical features from asymmetrical features on the waveform, which owes to its signal analysis operator: morphological Top-Hat transformation, an effective morphological technique. In this thesis, the MMTH scheme is employed in the identification of transformer magnetizing inrush curr~nt from internal fault. Decomposing the signal by MMTH, the asymmetrical features of the inrush waveform are exposed, and the other irrelevant components are attenuated. The MMG scheme adopts morphological gradient, a commonly used operator for edge detection in image and signal processing, as its signal analysis / operator. The MMG scheme bears significant property in characterizing and recognizing the sudden changes with sharp peaks and valleys on the waveform. Furthermore, to the MMG scheme, by decomposing the signal into different levels, the higher the level is processed, the more details of the sudden changes are revealed. In this thesis, the MMG scheme is applied for the design of fault locator of power transmission lines, by extracting the transient features directly from fault-generated transient signals. The MNTMG decomposition scheme can effectively reduce the noise and extract transient features at the same time. In this thesis, the MNTMG scheme is applied to extract the fault generated transient wavefronts from noise imposed signals in the application of fault location of power transmission lines. The proposed contributions focus on the effect of weighted dilation in the frequency domain, constructions of morphological multi-resolution decomposition schemes and their applications in power systems.

The purpose of this project was to build a computer model able of running virtual simulations and emulations of fuel cell (FC) systems. This was aimed at the transport market and modern built environment. The project incorporates the novel use of hardware, firmware and software operating in real-time to simulate real applications in vehicles and buildings. A fuel cell system is a complex assembly of components, all of which are all critical to its performance. To get the best from the system each of the system components must be optimized. Current practice uses prototyping of real hardware and testing. Such work is specific to single FC suppliers and is based on off-line modeling or real-time analysis against monitored loads. The innovation in this project is in integrating the optimization step into the development of the complete system. The technical breakthrough is shown through closing the development gap between concept and final design by creating a real-time simulation and emulation process to develop optimum FC systems for the transport and built environment markets. The virtual fuel cell can be operated safely outside the limits that it would normally encounter for given criteria. This extends the know-how beyond conventional testing. The time consuming and costly setting up of hardware tests with an actual fuel cell is therefore not required. This project outcome gives the new ability to design and engineer optimized FC systems without the risk of component / subsystem redundancy. It relinquishes the requirement for a hydrogen source, cooling; pumps, water etc. and gives rise to a completely safe test environment.

Eddy current sensing technique is widely used primarily because of its high tolerance to harsh environments, low cost, broad bandwidth and ease of automation. And its variant, pulsed eddy current offers richer information of target materials. However, accurate detection and characterisation of defects remains a major challenge in the petro-chemical industry using this technique which leads to spurious detection and false alarm. A number of parameters are contributory, amongst which is the inhomogeneity of the materials, coupling variation effect and relatively large lift-off effect due to coating layers. These sometimes concurrently affect the response signal. For instance, harsh and dynamic operating conditions cause variation in the electrical conductivity and magnetic permeability of materials. Also, there is the increased need to detect defects and simultaneously measure the coating layer. In practice therefore, multi-sensing modalities are employed for a comprehensive assessment which is often capital intensive. In contrast to this, multiple parameter delineation and estimation from a single transient response which is cost-effective becomes essential. The research concludes that multiple parameter delineation helps in mitigating the effect of a parameter of interest to improve the accuracy of the PEC technique for defect detection and characterisation on the one hand and for multi-parameter estimation on the other. This research, partly funded by the Petroleum Technology Development Fund (PTDF), proposes use of a novel multiple parameter based pulsed eddy current NDT technique to address the challenges posed by these factors. Numerical modelling and experimental approaches were employed. The study used a 3D finite element model to understand, predict and delineate the effect of varying EM properties of test materials on PEC response; which was experimentally validated. Also, experimental studies have been carried out to demonstrate the capabilities of the proposed to estimate multiple parameters vis-à-vis defect depth (invariant of lift-off effects) and lift-off. The major contributions of the research can be summarised thus: (1) numerical simulation to understand and separate the effect of material magnetic permeability and electrical conductivity in pulsed eddy current measurements and experimental validation; (2) proposed the lift-off point of intersection (LOI) feature for defect estimation invariant of lift-off effects for ferromagnetic and non-ferromagnetic samples; a feature which is hitherto not apparent in ferromagnetic materials (a primary material used in the oil and gas industry); (3) separation and estimation of defect and the lift-off effects in magnetic sensor based pulsed eddy current response; and (4) application of the LOI feature and demonstration of increased defect sensitivity of the PEC technique with the proposed feature in both ferrous and non-ferrous conductive materials.

Recently, Distributed Generation (DG) technologies become more potential in electricity supply contributors to electric utilities. It leads to increase the grid integration ratio of DG. Thus, the trend of decentralized power systems has been considered as a future of energy supply systems. According to this fact, the distribution systems must be changed from a passive control area to be an active control area. To overcome and realize this issue, the clustering power systems approach is developed. The main idea of this concept is to coexist the DG with the conventional power systems. Therefore, the system structure and the control approach are introduced and developed based on the conventional system. The cluster network structure keeps the main idea of conventional interconnected grid. Consequently, the clustering power systems concept intends to cluster the power systems into several areas, called cluster area. As a direct result, the cluster network structure can be described like the interconnected grids. In order to empower and turn the ordinary passive distribution system to be the active system, the clustering approach announces the distribution management system (DMS) for the cluster automation application. The DMS application is the cluster controller and management, which applies in each cluster area. To accomplish the DMS functionality, control functions based on cluster concept have been developed continuously, e.g. the multi-level clusters control approach. Besides the development of cluster control approach, a cluster analysis strategy is cautiously considered as well, since it is a key to complete a cluster management and an optimization process. A hybrid calculation technique is consequently proposed to be a solution for cluster analysis, because it offers a possibility to integrate a character of interconnected clusters into the analysis. Hence, the cluster analysis can be employed in a decoupling way. To evolve the cluster analysis, a character of distribution network has to be taken into account. The character of distribution network is dominated by the unbalanced condition e.g. multi-phase feeder system. Moreover, the penetration of DG units can cause unbalanced condition as well, e.g. single phase feed in of home PV systems. To deal with unbalanced condition, an asymmetrical sequence hybrid and asymmetrical three-phase fourwire hybrid analysis method is rolled out, both are developed based on a difference issue of load flow studies. All in all, the cluster analysis is a key to execute optimization and management process of cluster system operation as well as the supervisory of automated cluster control application. Finally, the proposed hybrid analysis is ready to be the main function in order to ensure and forwards the development of clustering power systems philosophy to be one of the best solutions for the future smart gird applications.

Mixed ionic-electronic conductive (MIEC) perovskite material La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF6428) is a promising candidate for the cathode in intermediate temperature solid oxide fuel cells (IT-SOFCs). Understanding the three dimensional (3D) microstructural characteristics of such a material is crucial to its application because they predominately determine the performance and durability of the porous cathodes and hence of the SOFCs. They affect the overall cathode kinetics and thus the electrochemical reaction efficiency, as well as the mechanical properties, which dominate the lifetime of SOFCs. It is necessary to balance the trade-off between the electrochemical performance, which is improved by high porosity and minimal sintering, and the ability to withstand mechanical constraints, which is improved by the opposite. To date LSCF6428 has been widely investigated on subjects of microstructure-related electrochemical performance, while little work has been reported on the mechanical properties and their correlation with the 3D microstructures. The main purpose of this research was to study the mechanical properties (i.e. elastic modulus, hardness and fracture toughness) of LSCF6428 cathode films and bulk samples fabricated by high temperature sintering, and to evaluate the effect of 3D microstructural parameters on elastic modulus, and the Poisson's ratio where applicable, by means of both experimental and numerical methods. Room-temperature mechanical properties were investigated by nanoindentation of porous bulk samples and porous films sintered at temperatures from 900 to 1200 °C. A spherical indenter was used so that the contact area was much greater than the scale of the porous microstructure. The elastic modulus of the bulk samples was found to increase from 33.8 to 174.3 GPa and hardness from 0.64 to 5.32 GPa as the porosity decreased from 45 to 5 vol% after sintering at 900 to 1200 °C. Densification under the indenter was found to have little influence on the measured elastic modulus. The residual porosity in the nominally dense sample was found to account for the discrepancy between the elastic moduli measured by nanoindentation and by impulse excitation. Based on the optimisation of a commercial LSCF6428 ink formulation, crack-free films of acceptable surface roughness for indentation were also prepared by sintering at 900 to 1200 °C. It was shown that reliable measurements of the true properties of the films were obtained by data extrapolation provided that the effects from both surface roughness and substrate were minimised to neglected levels within a certain range of indentation depth to film thickness ratio (which was 0.1 to 0.2 in this study).The elastic moduli of the films and bulk materials were approximately equal for a given porosity. Based on the crack length measurements for Berkovich-indented samples, the fracture toughnesses of bulk LSCF6428 were determined to increase from 0.51 to 0.99 MPa·m1/2, after sintering at 900 to 1200 °C. The microstructures of films before and after indentation were characterised using FIB/SEM slice and view technique and the actual 3D microstructure models of the porous films were reconstructed based on the tomographic data obtained. Finite element modelling of the elastic modulus of the resulting microstructures showed excellent agreement with the nanoindentation results. The 3D microstructures were numerically modified at constant porosity by applying a cellular automaton algorithm based method, so that the influence on elastic modulus of factors other than porosity could be evaluated. It was found that the heterogeneity of the pore structure has a significant influence on the elastic properties computed using mechanical simulation.

Solid oxide cells (SOCs) are promising energy conversion devices in which the chemical energy of fuels is converted into electrical energy in an efficient manner. It is generally accepted that electrode microstructure plays an important role in determining the performance and durability of SOCs. The electrode is required to contain large amount of active reaction sites, termed triple phase boundaries (TPBs), to promote the electrochemical reaction. At the same time, effective transport pathways need to be established to and from each TPB. Therefore, the microstructure-performance relationships need to be understood in order to develop highly efficient electrodes. In this study a novel electrode, prepared by infiltration of nickel nano-particles into Gadolinium doped Ceria porous scaffold, is proposed. The research aims to understand the fundamental phenomena underpinning SOC operation for steam electrolysis/H2 oxidation in these electrodes and to establish the relationship between the microstructure of the infiltrated electrode and electrode performance. The electronic conductivity of infiltrated electrodes was tested by the van der Pauw method over the temperature range 20-700 °C. Electrochemical behaviour was assessed for fuel cell and electrolysis modes using three electrode AC and DC measurements. The microstructure was studied by SEM and FIB techniques, including 3-D imaging and quantification. Ultimately, this is to allow electrodes to be designed with desired characteristics. In addition, a novel approach for electrode preparation by Selective Laser Sintering (SLS) was evaluated by conducting a proof of concept study. This fabrication technique enables the porosity and pattern of the electrode to be controlled by regulating the parameters of the laser (laser power and laser speed). The feasibility of using this novel technique for solid oxide cells was demonstrated. A method for the fabrication of high performance 'electrodes by design' through the combination of the two techniques in which the scaffold preparation by SLS is followed by infiltration is in prospect.

Fuel cells are electrochemical devices that convert chemical fuels directly into electricity, heat, and waste products with higher efficiencies than many conventional combustion technologies. Fuel cells have already found applications in automotive and domestic applications, where their high efficiencies offer potential reductions in CO2 emissions as well as energy savings. A promising technology is the solid oxide fuel cell (SOFC), which typically runs at temperatures between 500 - 1000C, and can convert hydrogen rich gases, such as methane, directly into heat and electricity. This thesis presents work on developing improved atomistic models of yttria stabilised zirconia (YSZ), which is used as a catalyst support and electrolyte material in a solid oxide fuel cell. The catalyst, YSZ, and a gas phase containing fuel molecules, meet at the anode to form the anode triple phase boundary (TPB) in an SOFC. The anode TPB is the site at which fuel molecules undergo electrochemical oxidation, a process that releases electrons and waste products. Unfortunately the anode is susceptible to poisoning and damage through detrimental chemical reactions which can lead to carbon deposition and sulphur poisoning. A long term aim for the field of SOFC catalysis is to understand these reactions and design improved catalysts which are resistant to contamination processes. However, to date, the detailed mechanisms involved in these reactions have not been established; even the mechanism for the oxidation of hydrogen at the anode TPB is fiercely debated. For these reasons, there is interest in developing atomistic models of the anode TPB to investigate the thermodynamics of possible reaction paths. Modeling the anode TPB is dependant on many factors including: materials, surface structure, interfaces, distribution of local defects. A detailed knowledge of the YSZ surface chemistry is currently inhibited by a poor understanding of the distribution and local atomistic structure of the dopant Y3+ ions and oxygen vacancies in the bulk crystal and at the surfaces. In this thesis, a comprehensive search for low energy defect structures using a combined classical modeling and density functional theory (DFT) approach is used to identify the low energy defect structures of 3.2mol% YSZ. 3.2mol% YSZ is chosen as the limit of low dopant concentration and as a simple system to investigate, avoiding the the combinatorial complexity of higher dopant concentrations and defect-defect interactions. Through analysis of energetics computed using; the best available empirical potential model, point charges, DFT, and local strain energy estimated in the harmonic approximation, we examine the main chemical and physical interactions that determine the low energy structures. It is found that the empirical potential model reproduces a general trend of increasing DFT energetics across a series of locally strain relaxed structures, but is unreliable both as it predicts some incorrect low energy structures, and because it finds some meta-stable structures to be unstable. A better predictor of low energy defect structures is the total electrostatic energy of a simple point charge model calculated at the unrelaxed geometries of the defects. In addition, the strain relaxation energy is substantial, and is estimated effectively in the harmonic approximation to the imaginary phonon modes of cubic zirconia (c-ZrO2), but it is not a determining factor for the relative stabilities of low energy defect structures. These results allow us to propose a simple method for identifying low energy YSZ defect structures. The findings from the studies of bulk 3.2mol% YSZ are used to establish the low energy structures of a 3.2mol% YSZ (111) surface model. After initially demonstrating that a slab model, much larger than that used in previous DFT studies is required to obtain a converged surface energy, the energetic preference for yttrium to segregate to the (111) surface is investigated. After establishing that yttrium indeed segregates to the (111) surface, we compute the DFT energies of 20 low energy symmetry inequivalent surface structures, and identify the preferential defect configurations and surface chemistry sites. In addition, the DFT energy of the low energy NN structure proposed by Reaxff modeling is computed. It is shown that this structures is significantly higher in energy than our minimum energy structure, which has NNN geometry. This highlights the need for large scale DFT calculations in understanding the YSZ (111) surface structure. Having obtained atomistic structures for the surface reaction sites, water dissociation onto the lowest energy YSZ (111) surface is investigated. It is shown that it is preferable for water to associatively adsorb to the YSZ surface, and this is optimal when water adsorbs to the yttrium site. Dissociative adsorption of water is only possible over zirconium sites with the process generally being endothermic. Some exothermic paths for dissociative adsorption exist, however there are large energy barriers to the process. Associative adsorbtion to the surface yttrium site is the global minimum of the system, and yttrium sites appear to act as a trap for water molecules. Finally, the methodology developed in previous sections is used to investigate the 6.7mol% YSZ system, which is closer to the Y2O3 dopant concentration used in most commercial SOFCs (8 - 10 mol%). It is found that, whereas the electrostatic energy of the unrelaxed structures calculated using a point charge model was a good predictor of the likely low energy 3.2mol% defect structures, it is a poor predictor of the likely low energy 6.7mol% defect structures. In addition, while it was found that the best available Born-Mayer-Huggins potential model recreated general trends in DFT energies at 3.2mol%, it completely fails to reproduce DFT energy differences at 6.7mol%. In the absence of an easy to calculate, reliable predictor of the likely low energy DFT defect structures, we correlate the formation energies of the structures to simple geometric parameters. We perform an exhaustive search on 2857 symmetry inequivalent structures, characterising every structure in terms of intuitive quantities, such as: vacancy - vacancy separation, the average vacancy - Y3+ interatomic separation, the average Y3+ - Y3+ interatomic speration, the surface area occupied by the defect cluster, and the volume of the defect cluster. It is possible to explain the electrostatic formation energies of the defects in terms of intuitive attractive and repulsive forces and to find weak trends between the geometric descriptors and the final relaxed DFT energies, however, without an extensive database of fully relaxed DFT energies, it is hard to determine the statistical meaning of these results. This result highlights the combinatorial complexity of the 6.7mol% system and establishes the need for further large scale DFT calculations on the 6.7 mol% system.

No description available.