Browsing by Subject "Flexible"
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Item Development of solution processed, flexible, CuInSe₂ nanocrystal solar cells(2018-01-23) Voggu, Vikas Reddy; Korgel, Brian Allan, 1969-; Ekerdt, John G; Milliron, Delia; Truskett, Thomas; Vanden Bout, David AClean sources of energy, especially photovoltaics (PVs), are urgently needed to cope with global energy shortage and environmental pollution. For PVs to play a significant role in energy production, the current prices must be brought down. Thin film PVs made using layered Mo or Au/CuInGaSe₂(CIGS)/CdS/ZnO/ITO have already shown high efficiencies. Traditionally, most layers in CIGS solar cells are deposited using high-cost techniques requiring high temperatures and ultra-low pressures. By replacing the traditionally processed CIGS with a nanocrystal layer that can be deposited at mild processing conditions, the fabrication cost can be reduced. In this study, a high yielding synthesis method for CuInSe₂ nanocrystals has been developed which gives the best efficiency (3.1%), so far, for low-temperature processed CuInSe₂ nanocrystal PVs. An important challenge that nanocrystal solar cells currently face is low device efficiency, resulting in higher operating cost. CuInSe₂ nanocrystals can remain suspended in solution because of the long chain organic ligands attached to the surface. However, these ligands hinder charge transfer between nanocrystals causing low device efficiency. These ligands have been successfully replaced with smaller sulfide ions thereby improving the best efficiency of low-temperature processed CuInSe₂ nanocrystal solar cells from 3.1 % to 3.5%. Another approach to reducing the cost of CuInSe₂ PVs is by replacing the glass support medium with cheaper alternatives like paper. Flexible CuInSe₂ nanocrystal solar cells are successfully fabricated on paper with efficiencies reaching up to 2.25%. This is the first time a nanocrystal solar cell has been fabricated on paper. There is no significant loss in PV device performance after more than 100 flexes to 5 mm radius, and the devices continue to perform when folded into a crease. Apart from the absorber layer, the replacement of other high-temperature and vacuum processed device layers with ambient solution-processed layers lowers the manufacturing cost. This has been achieved by spin coating suitable nanomaterials as device layers. Lastly, for commercialization of CuInSe₂ nanocrystal solar cells, multiple devices need to be connected to achieve the desired current and voltage. A fabrication process has been developed for building multiple nanocrystal PVs on a single substrate using 3D printed masksItem A flexible display system for embedded applications(2013-05) Slowik, Matthew Caldwell; Aziz, AdnanFlat electronic displays are ubiquitous in our environment from small handheld devices to large HDTVs. This report documents the design and development of a flexible electronic display system for low cost embedded applications. The main use of such a device would be in functions where flat displays are too rigid and too brittle to operate, like the emerging wearable electronics sector. A 10cm x 15cm, 224 pixel LED mesh display system is presented as a solution. A complete software stack was created in conjunction with the hardware. On the software side, a Visual Basic application allows users to easily generate image content for the display, five different global motion algorithms permit real time image manipulation, and an AVR assembly procedure handles screen refreshing. Altogether the system weighs 176 grams, can function under normal operating conditions for eight hours before recharging is required, and costs under $85 without volume discounts.Item Nanoscale graphene for RF circuits and systems(2013-08) Parrish, Kristen Nguyen; Akinwande, DejiIncreased challenges in CMOS scaling have motivated the development of alternatives to silicon circuit technologies, including graphene transistor development. In this work, we present a circuit simulator model for graphene FETs, developed to both fit measured data and predict new behaviors, motivating future research. The model is implemented in Agilent ADS, a circuit level simulator that is commonly used for non-standard transistor technologies, for use with parameter variation analyses, as well as easy integration with CMOS design kits. We present conclusions drawn from the model, including analyses on the effects of contact resistance and oxide scaling. We have also derived a quantum-capacitance limited model, used to intuit intrinsic behaviors of graphene transistors, as well as outline upper bounds on performance. Additionally, the ideal frequency doubler has been examined and compared with graphene, and performance limits for graphene frequency multipliers are elucidated. Performance as a demodulator is also discussed. We leverage this advancement in modeling research to advance circuit- and system-level research using graphene transistor technology. We first explore the development of a GHz planar carbon antenna for use on an RF frontend. This research is further developed in work towards the first standalone carbon radio on flexible plastics. A front end receiver, comprised of an integrated carbon antenna, transmission lines, and a graphene transistor for demodulation, are all fabricated onto one plastic substrate, to be interfaced with speakers for a full radio demo. This complete system will motivate further research on graphene-on-plastic systems.Item Tool Path Generation for Flexible Blade Cutting(2000) Broek, Han J.; Horváth, Imre; Smit, Bram deFree Form Thick Layered Object Manufacturing FF-TLOM is based on application of a reshapeable cutting device, which allows a free form shaping of thick polystyrene foam layers. Once manufactured, these layers are stacked to produce a physical model. Tool path generation for the heated flexible blade tool is a challenging task, since it influences the quality of the manufactured objects as well as the effectiveness of the fabrication process. Them difficulties arise from the following facts: (a) when slicing is computed, the instantaneous tool positions are defined by matching the blade profile against the nominal shape of the CAD model, (b) the tool positions calculated relative to the cut layers have to be converted into the global reference frame of the layer cutting equipment, (c) the resultant tool path should maintain the achieved preciseness approximating the front surface of the layers, and (d) it is impossible to calculate all points of the tool path in real time. This paper proposes an effective tool path calculation method for flexible blade cutting. The contour of the layers is converted into an ordered set of smooth and awkward boundary features. For the smooth boundary features, the tool positions are computed by dense sampling in order to achieve the optimal cutting.Item Wafer scale exfoliation of monocrystalline micro-scale silicon films(2018-02-14) Ward, Martin John; Cullinan, MichaelThis thesis presents a new method and tool for controlling the thicknesses and quality of exfoliated monocrystalline silicon thin-films. The resulting films can be used to create high-performance and cost-effective flexible electronic devices. A finite element linear elastic fracture mechanics study was performed to understand the parameters that control the exfoliation process. Then a metamodel was created from the simulation results to inform the design and operation of a new exfoliation tool. This new tool creates a controlled peeling force that propagates the crack in a precise manner. A new metrology system was developed using a combination of laser displacement sensors and confocal microscopy to characterize the quality of the exfoliated films. The results of the new process show improvement in the uniformity and quality of the exfoliation compared to previous methods and confirms the ability of the new tool to steer the crack trajectory.