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<p>The photovoltaics (PV) research community is currently pursuing many approaches to reduce the cost of PV and increase the energy conversion efficiency. Single-crystalline silicon (sc-Si) solar cells are able to achieve high efficiency but have a higher cost relative to other technologies. It may be possible to drastically reduce the cost of sc-Si PV by fabricating solar cells which are an order of magnitude thinner than conventional solar cells, i.e. thinner than 30 microns. Aside from new fabrication paradigms, ultra-thin sc-Si solar cells require advanced light-trapping techniques to enhance the absorption of long-wave radiation which is otherwise transmitted through the cell. In this thesis, a novel process flow for the fabrication of ultra-thin sc-Si solar cells in the laboratory was designed and implemented with the aim of testing light-trapping structures in the context of actual ultra-thin sc-Si devices. The process flow uses 10 micron thick sc-Si membranes, 0.95 cm in diameter, fabricated on silicon-on-insulator wafers using double-sided processing. The best fabricated device incorporated a back surface field, a white paint diffuse rear reflector and a silicon nitride antireflection coating. It achieved a fill factor, efficiency, short circuit current and open circuit voltage of 0.67, 9.9%, 27.9 mA cm^-2 and 0.53 V respectively. Simulations suggest the device efficiency can approach 15.4% without light-trapping and 16.5% with a diffuse rear reflector as a light trapping structure. This process flow is intended to be used as a platform on which to test further light-trapping structures with the continuation of this project.</p> / Master of Applied Science (MASc)

<p>Preparing silicon wafers is a tedious multi-step process that includes etching, polishing, and cleaning. The minimum wafer thickness attainable in current high volume wafer production processes is generally 160 to 300 μm, and the kerf loss for these processes is up to 40% of the total volume. Thin silicon wafers (~30 to 100μm) are very expensive to produce and the wafering process is not cost effective due to the high amount of material loss (more than 80% at these dimensions) during the process and the risk of breakage of the wafers during wafering. In this thesis, a new method called Vapour-Liquid Interface Growth (VLIG) is proposed. VLIG is capable of directly growing a sheet of single crystal silicon without wafering with a thickness of about 30 to 50μm. The features of the process are 1) low temperature operation; 2) the resulting silicon sheet is easily detachable and self-supporting; 3) the resulting sheet has uniform thickness and is single crystal. The system operates in a supersaturated growth solution of an indium-silicon melt. A seed line in a substrate facing down is employed. A layer of single crystal silicon grows on the seed line at the melt surface due to surface segregation during the super cooling process. The grown silicon can grow laterally due to the limited thickness of the melt depth that minimizes growth in the vertical growth direction. The grown silicon can be easily peeled off from the seed line substrate due to the presence of a gap between the grown silicon sheet and the oxide layer on the seed line substrate. The self-supporting silicon sheet now comprises a very thin silicon substrate or sheet.</p> <p>VLIG silicon sheet is characterized by X-ray diffraction to determine the crystallinity. Hall Effect measurements are performed to measure the electrical properties. VLIG silicon sheet is (111) oriented single crystal and it exhibits the same orientation as the substrate. The growth temperature is from 975 to 850^oC, and the VLIG silicon is p-type doped with indium. The resistivity is 4.181x10^-3 ohm-cm, and the doping level is around 5.3.0x10¹⁸ /cm3. The measured mobility is ranging from 280 cm²/V.s. In this study, VLIG demonstrates the potential of growing thin sheet of single crystal silicon with qualities that feasible for photovoltaic application.</p> / Master of Applied Science (MASc)

Vacuum forming is a popular, cost effective method amongst large and small scale applications. The method is used to mold a material to the surface of a mold/pattern in order to create a negative copy for reproduction or an object in positive form. The prototype vacuum forming system developed and documented herein is of a membrane-seal type that consists of three (3) principle parts: radial platen, Hinged Frame and Platen Support Assembly, and a PVC surge tank. Each part is described in detail through design, manufacturing, and testing processes. The design supports functional versatility, small scale molding, and uses readily available materials. Functional prototype testing was performed with the thermoplastic KYDEX® and multiple objects for mold examples. Results include successful proof of concept, design pros and cons, and findings based on functional testing.

Wood composites are widely used in construction applications because of their superior dimensional and structural attributes over raw wood products. However, current wood composite manufacturing practices, which rely on thermal-curing of adhesives, are expensive, energy intensive, time consuming and are prone to manufacturing defects. Use of radiation curable adhesives (RCAs) could potentially answer all of these issues. Specifically, use of electron-beam (e-beam) radiation has been increasing in areas of research and industry where rapid, low-temperature polymerization is required and low energy consumption is desired. For e-beams to be used in wood composites, however, it must be determined whether or not the wood is structurally impacted by irradiation, and to what extent. Maple beams irradiated with a range of e-beam dosages were studied in three-point bend tests to assess the changes in bulk properties of the wood, and were further studied with infrared spectroscopy to identify chemical changes resulting from the radiation treatments. Also, dynamic mechanical analysis (DMA) was performed on maple veneers treated with the same doses of radiation to characterize changes in the viscoelastic properties. Furthermore, while RCAs and their curing have been studied, it is important to understand if the presence of wood will impede the polymerization of these adhesives, and to what extent. Maple veneers impregnated with one of two resins were cured with the same e-beam dosages and investigated by means of DMA and FTIR spectroscopy. Swelling tests were conducted to detect interaction between the resins and the wood, which would indicate good interfacial bonding in the composite matrix. Notable loss of strength was observed in the irradiated wood, especially at 180kGy. Monitoring the glass transition temperature (Tg) and activation energy (Ea) derived from DMA revealed that the most destructive trends in the wood began around 80kGy. Cure of resins in the composites was hindered by the presence of the wood, but both resins did eventually reach complete cure at doses higher than what the neat resins required. Interaction between the resins and the wood was evident. In the end, results indicate that there is a range of radiation dosages in which the resin in a wood composite can be cured without destroying the structural integrity of the wood.

The use of sunlight has always been a major goal in the design and operation of commercial buildings to minimize electrical consumption of artificial lighting systems. Glazing systems designed to allow optimal visible light transmission also allow significant unwanted direct solar heat gain caused by infrared light. Conversely, glazing systems that are designed to reflect unwanted direct solar heat gain significantly reduce the transmittance of visible light through windows. The goal of this research was to characterize the performance of water as gap-fill for double-glazing units in eliminating the compromises that exist in current glazing systems with respect to light and heat transmittance. An in situ test approach and computer simulations were conducted to measure the performance of water-filled glazing units against air-filled glazing units. The thermal transmittance and solar heat gain coefficient values obtained from both the field experiments and computer simulations, glazing units with air-fill proved better than the glazing units with non-flowing water-fill. However, the high convective coefficient and the high thermal mass of the water can be used to its advantage when it is allowed to flow at peak temperatures, thus, maintaining lower temperature swings indoor. This can lead to a reduction of about 50-70% direct solar heat and still maintain high visibility.

The search for new and additional sources of energy -- from sun, wind, waves, and ocean currents -- is necessitating the development of structures in the open environment of the oceans as well as on land. The advantages of round or tubular members for use in such structures are shown; and to avoid the uncertainties of welded joints, two bolted connections are proposed and their feasibility explored.

In this investigation, the primary objective was to study the nonlinear behavior of unbraced two-bay concrete frames and to determine the extent to which ultimate load theory or limit design can be applied to these structures. The frame behavior was investigated analytically by two methods. In the first method the frame stability equation was derived assuming that members of the frame possess an elasto-plastic moment-curvature relationship. This stability analysis was also carried out by another model consisting of a column attached to a linear spring and carrying the total frame load. The second method was through a computer program which took material and geometric nonlinearities of concrete frames into account. A model concrete frame, with a scale factor of approximately one-third was considered. Variable parameters were loading condition, column reinforcement ratio, and beam to column load ratio. For each frame, the gravity loads were increased proportionally until 75% of the frame ultimate capacity under gravity loads was reached. Then; while these gravity loads were held constant, lateral load was applied and increased to failure. The overall geometry, 21-in high columns and 84-in long beam, were kept the same for all of model frames investigated. The computer study and the stability model analysis indicated that all frames remained stable until four plastic hinges (two in each bay) formed, thus producing a combined sway mechanism. Based on the scope of this study, it appears that limit design may be employed for unbraced reinforced concrete structures.