Matching Items (20)
Filtering by
- All Subjects: Electrical Engineering
- All Subjects: solar
Description
Silicon solar cells with heterojunction carrier collectors based on a-Si/c-Si heterojunction (SHJ) have a potential to overcome the limitations of the conventional diffused junction solar cells and become the next industry standard manufacturing technology of solar cells. A brand feature of SHJ technology is ultrapassivated surfaces with already demonstrated 750 mV open circuit voltages (Voc) and 24.7% efficiency on large area solar cell. Despite very good results achieved in research and development, large volume manufacturing of high efficiency SHJ cells remains a fundamental challenge. The main objectives of this work were to develop a SHJ solar cell fabrication flow using industry compatible tools and processes in a pilot production environment, study the interactions between the used fabrication steps, identify the minimum set of optimization parameters and characterization techniques needed to achieve 20% baseline efficiency, and analyze the losses of power in fabricated SHJ cells by numerical and analytical modeling. This manuscript presents a detailed description of a SHJ solar cell fabrication flow developed at ASU Solar Power Laboratory (SPL) which allows large area solar cells with >750 mV Voc. SHJ cells on 135 um thick 153 cm2 area wafers with 19.5% efficiency were fabricated. Passivation quality of (i)a-Si:H film, bulk conductivity of doped a-Si films, bulk conductivity of ITO, transmission of ITO and the thickness of all films were identified as the minimum set of optimization parameters necessary to set up a baseline high efficiency SHJ fabrication flow. The preparation of randomly textured wafers to minimize the concentration of surface impurities and to avoid epitaxial growth of a-Si films was found to be a key challenge in achieving a repeatable and uniform passivation. This work resolved this issue by using a multi-step cleaning process based on sequential oxidation in nitric/acetic acids, Piranha and RCA-b solutions. The developed process allowed state of the art surface passivation with perfect repeatability and negligible reflectance losses. Two additional studies demonstrated 750 mV local Voc on 50 micron thick SHJ solar cell and < 1 cm/s effective surface recombination velocity on n-type wafers passivated by a-Si/SiO2/SiNx stack.
ContributorsHerasimenka, Stanislau Yur'yevich (Author) / Honsberg, C. (Christiana B.) (Thesis advisor) / Bowden, Stuart G (Thesis advisor) / Tracy, Clarence (Committee member) / Vasileska, Dragica (Committee member) / Holman, Zachary (Committee member) / Sinton, Ron (Committee member) / Arizona State University (Publisher)
Created2013
Description
Based on theoretical calculations, a material that is highly transmissive below 3000 nm and opaque above 3000 nm is desired to replace glass covers for flat plate solar thermal systems. Additionally, a suitable replacement material needs to have a sufficiently high operating temperature in order to prevent the glazing from melting and warping in a solar system. Traditional solar thermal applications use conventional soda lime glass or low iron content glass to accomplish this; however, this project aims to investigate acrylic, polycarbonate, and FEP film as suitable alternatives for conventional solar glazings. While UV-Vis and FT-IR spectroscopy indicate that these polymer substitutes may not be ideal when used alone, when used in combination with coatings and additives, these materials may present an opportunity for a glazing replacement. A model representing a flat plate solar collector was developed to qualitatively analyze the various materials and their performance. Using gathered spectroscopy data, the model was developed for a multi-glazing system and it was found that polymer substitutes could perform better in certain system configurations. To complete the model, the model must be verified using empirical data and coatings and additives investigated for the purposes of achieving the desired materials optical specifications.
ContributorsBessant, Justin Zachary (Author) / Friesen, Cody (Thesis director) / Lorzel, Heath (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
As prices for fuel along with the demand for renewable resources grow, it becomes of paramount importance to develop new ways of obtaining the energy needed to carry out the tasks we face daily. Costs of production due to energy and time constraints impose severe limitations on what is viable. Biological systems, on the other hand, are innately efficient both in terms of time and energy by handling tasks at the molecular level. Utilizing this efficiency is at the core of this research. Proper manipulation of even common proteins can render complexes functionalized for specific tasks. In this case, the coupling of a rhenium-based organometallic ligand to a modified myoglobin containing a zinc porphyrin, allow for efficient reduction of carbon dioxide, resulting in energy that can be harnessed and byproducts which can be used for further processing. Additionally, a rhenium based ligand functionalized via biotin is tested in conjunction with streptavidin and ruthenium-bipyridine.
ContributorsAllen, Jason Kenneth (Author) / Ghirlanda, Giovanna (Thesis director) / Francisco, Wilson (Committee member) / Barrett, The Honors College (Contributor) / Chemical Engineering Program (Contributor)
Created2014-12
Description
The goal of this research was to identify why the federal government should invest in solar research and development, and which areas of solar improvement should be focused on. Motivation for this can be found in the pressing need to prevent and reverse the effects of climate change, the inevitability of fossil fuel resources eventually running out, and the economic and job creation potential which solar energy holds. Additionally, it is important to note that the best course of action will involve a split of funding between current solar rollout and energy grid updating, and the R&D listed in this research. Upon examination, it can be seen that an energy revolution, led by a federal solar jobs program and a Green New Deal, would be both an ethically and economically beneficial solution. A transition from existing fossil fuel infrastructure to renewable, solar-powered infrastructure would not only be possible but highly beneficial in many aspects, including massive job creation, a more affordable, renewable energy solution to replace coal-fired plants, and no fuel spending or negotiation required.<br/>When examining which areas of solar improvement to focus on for R&D funding, four primary areas were identified, with solutions presented for each. These areas for improvement are EM capture, EM conversion efficiency, energy storage capacity, and the prevention of overheating. For each of these areas of improvement, affordable solutions that would greatly improve the efficiency and viability of solar as a primary energy source were identified. The most notable area that should be examined is solar storage, which would allow solar PV panels to overcome their greatest real and perceived obstacle, which is the inconsistent power generation. Solar storage is easily attainable, and with enough storage capacity, excess solar energy which would otherwise be wasted during the day can be stored and used during the night or cloudy weather as necessary. Furthermore, the implementation of highly innovative solutions, such as agrivoltaics, would allow for a solar revolution to occur.
ContributorsWhitlow, Hunter Marshall (Author) / Fong, Benjamin (Thesis director) / Andino, Jean (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
Description
The investigation into wide band gap semiconductors for use in tandem solar cells has become an increasingly more researched area with many new absorbers outlining the landscape. Pairing silicon with another cheap wide band gap semiconductor absorber can generate more efficient solar cell, which could continue to drive up the energy output from solar. One such recently researched wide band gap absorber is ZnSnN2. ZnSnN2 proves too difficult to form under most conditions, but has the necessary band gap to make it a potential earth abundant solar absorber. The deposition process for ZnSnN2 is usually conducted with Zn and Sn metal targets while flowing N2 gas. Due to restrictions with chamber depositions, instead ZnO and SnO2 targets were sputtered with N2 gas to attempt to form separate zinc and tin oxynitrides as an initial single target study prior to future combinatorial studies. The electrical and optical properties and crystal structure of these thin films were analyzed to determine the nitrogen incorporation in the thin films through X-ray diffraction, UV-Vis spectrophotometry, and 4-point probe measurements. The SnO2 thin films showed a clear response in the absorption coefficient leading but showed no observable XRD peak shift. Thus, it is unlikely that substantial amounts of nitrogen were incorporated into SnO¬2. ZnO showed a clear response increase in conductivity with N2 with an additional shift in the XRD peak at 300 °C and potential secondary phase peak. Nitrogen incorporation was achieved with fair amounts of certainty for the ZnO thin films.
ContributorsTheut, Nicholas C (Author) / Bertoni, Mariana (Thesis director) / Holman, Zachary (Committee member) / Materials Science and Engineering Program (Contributor) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2019-05
Description
Fresh water is essential to the human population and is an integral component in global economics for its multiple uses, and population growth/development cause concern for the possible exhaustion of the limited supply of freshwater. A combined computational and experimental approach to observe and evaluate pervaporation membrane performance for brackish water recovery was done to assess its efficiency and practicality for real world application. Results from modeling conveyed accuracy to reported parameter values from literature as well as strong dependence of performance on input parameters such as temperature. Experimentation results showed improved performance in flux by 34%-42% with radiative effect and then additional performance improvement (9%-33%) with the photothermal effect from carbon black application. Future work will include improvements to the model to include scaling propensity and energy consumption as well as continued experimentation to assess quality of pervaporation in water recovery.
ContributorsDurbin, Mitchell (Co-author) / Rivers, Frederick (Co-author) / Lind Thomas, MaryLaura (Thesis director) / Durgan, Pinar Cay (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
As global population and demand for electrical power increase, humanity is faced with the growing challenge of harnessing and distributing enough energy to sustain the developing world. Currently, fossil fuels (coal
atural gas) are our main sources of electricity. However, their cost is increasing, they are nonrenewable, and they are very harmful to the environment. Thus, capacity expansion in the renewable energy sector must be realized to offset higher energy demand and reduce dependence on fossil fuels. Solar energy represents a practical solution, as installed global solar capacity has been increasing exponentially over the past 2 decades. However, even with government incentives, solar energy price ($/kWh) continues to be highly dependent on political climate and raw material (silicon and silver) cost. To realistically and cost effectively meet the projected expansions within the solar industry, silver must be replaced with less costly and more abundant metals (such as copper) in the front-grid metallization process of photovoltaic cells. Copper, while offering both higher achievable efficiencies and a raw material cost nearly 100 times cheaper than silver, has inherent disadvantages. Specifically, copper diffuses rapidly into the silicon substrate, requires more complex and error-prone processing steps, and tends to have less adhesive strength, reducing panel robustness. In this study, nickel deposition via sputtering was analyzed, as well as overall potential of nickel as a seed layer for copper plating, which also provides a barrier layer to copper diffusion in silicon. Thermally-formed nickel silicide also reduces contact resistivity, increasing cell efficiency. It was found that at 400 \u00B0C, ideal nickel silicide formation occurred. By computer modeling, contact resistivity was found to have a significant impact on cell efficiency (up to 1.8%). Finally, sputtering proved useful to analyze nickel silicide formation, but costs and time requirements prevent it from being a practical industrial-scale metallization method.
atural gas) are our main sources of electricity. However, their cost is increasing, they are nonrenewable, and they are very harmful to the environment. Thus, capacity expansion in the renewable energy sector must be realized to offset higher energy demand and reduce dependence on fossil fuels. Solar energy represents a practical solution, as installed global solar capacity has been increasing exponentially over the past 2 decades. However, even with government incentives, solar energy price ($/kWh) continues to be highly dependent on political climate and raw material (silicon and silver) cost. To realistically and cost effectively meet the projected expansions within the solar industry, silver must be replaced with less costly and more abundant metals (such as copper) in the front-grid metallization process of photovoltaic cells. Copper, while offering both higher achievable efficiencies and a raw material cost nearly 100 times cheaper than silver, has inherent disadvantages. Specifically, copper diffuses rapidly into the silicon substrate, requires more complex and error-prone processing steps, and tends to have less adhesive strength, reducing panel robustness. In this study, nickel deposition via sputtering was analyzed, as well as overall potential of nickel as a seed layer for copper plating, which also provides a barrier layer to copper diffusion in silicon. Thermally-formed nickel silicide also reduces contact resistivity, increasing cell efficiency. It was found that at 400 \u00B0C, ideal nickel silicide formation occurred. By computer modeling, contact resistivity was found to have a significant impact on cell efficiency (up to 1.8%). Finally, sputtering proved useful to analyze nickel silicide formation, but costs and time requirements prevent it from being a practical industrial-scale metallization method.
ContributorsBliss, Lyle Brewster (Author) / Bowden, Stuart (Thesis director) / Karas, Joseph (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
Description
To compete with fossil fuel electricity generation, there is a need for higher efficiency solar cells to produce renewable energy. Currently, this is the best way to lower generation costs and the price of energy [1]. The goal of this Barrett Honors Thesis is to design an optical coating model that has five or fewer layers (with varying thickness and refractive index, within the above range) and that has the maximum reflectance possible between 950 and 1200 nanometers for normally incident light. Manipulating silicon monolayers to become efficient inversion layers to use in solar cells aligns with the Ira. A Fulton Schools of Engineering research themes of energy and sustainability [2]. Silicon monolayers could be specifically designed for different doping substrates. These substrates could range from common-used materials such as boron and phosphorus, to rare-earth doped zinc oxides or even fullerene blends. Exploring how the doping material, and in what quantity, affects solar cell energy output could revolutionize the current production methods and commercial market. If solar cells can be manufactured more economically, yet still retain high efficiency rates, then more people will have access to alternate, "green" energy that does not deplete nonrenewable resources.
ContributorsSanford, Kari Paige (Author) / Holman, Zachary (Thesis director) / Weigand, William (Committee member) / Industrial, Systems (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
CdTe/MgCdTe double heterostructures (DHs) integrated with a heavily-doped a-Si:H layer as the hole contact was demonstrated a record open-circuit voltage (VOC) of 1.11 V and an active-area efficiency of 20% in 2016. Despite this significant progress, some of the underlying device physics has not been fully understood. The first part of this dissertation reports a systematic study of the CdTe/MgCdTe DH devices. The CdTe/MgCdTe DHs are grown on InSb(001) substrates. The vertical transport mechanisms across the CdTe and InSb heterovalent interface are investigated with N-CdTe/n-InSb and N-CdTe/p-InSb heterostructures. A transport model including tunneling through CdTe barrier and InSb interband transition is developed to explain the different temperature dependent current-voltage characteristics of these two heterostructures.
Different p-type layers are integrated with the CdTe/MgCdTe DHs to form solar cells with different VOC values and efficiencies. The low VOC of devices with ZnTe:Cu and ZnTe:As hole contacts is attributed to the low built-in voltage and reduced minority carrier lifetime in the CdTe absorber, respectively. The critical requirements for reaching high VOC values are analyzed.
A novel epitaxial lift-off technology for monocrystalline CdTe is developed using a water-soluble and nearly lattice-matched MgTe sacrificial layer grown on InSb substrate. The freestanding CdTe/MgCdTe DH thin films obtained from the lift-off process show improved optical performance due to enhanced light extraction efficiency and photo-recycling effect. This technology enables the possible development of monocrystalline CdTe thin-film solar cells and 1.7/1.1-eV MgCdTe/Si or MgCdTe/Cu(InGa)Se2 tandem solar cells. The monocrystalline CdTe thin-film solar cells and 1.7-eV MgCdTe DH solar cells have been demonstrated with a power conversion efficiency of 9.8% and an active-area efficiency as high as 15.2%, respectively. Additionally, a study of the radiation effects on CdTe DHs under 68-MeV proton irradiation is performed and showed their superior radiation tolerance. All these findings indicate that the monocrystalline CdTe thin-film solar cells are reasonably expected to have low weight, high-efficiency and high power density, ideal for space applications.
ContributorsDing, Jia (Author) / Zhang, Yong-Hang (Thesis advisor) / Vasileska, Dragica (Committee member) / Johnson, Shane (Committee member) / Holman, Zachary (Committee member) / Arizona State University (Publisher)
Created2021
Description
Patterning technologies for micro/nano-structures have been essentially used in a variety of discipline research areas, including electronics, optics, material science, and biotechnology. Therefore their importance has dramatically increased over the past decades. This dissertation presents various advanced patterning processes utilizing cross-discipline technologies, e.g., photochemical deposition, transfer printing (TP), and nanoimprint lithography (NIL), to demonstrate inexpensive, high throughput, and scalable manufacturing for advanced optical applications.
The polymer-assisted photochemical deposition (PPD) method is employed in the form of additive manufacturing (AM) to print ultra-thin (< 5 nm) and continuous film in micro-scaled (> 6.5 μm) resolution. The PPD film acts as a lossy material in the Fabry-Pérot cavity structures and generates vivid colored images with a micro-scaled resolution by inducing large modulation of reflectance. This PPD-based structural color printing performs without photolithography and vacuum deposition in ambient and room-temperature conditions, which enables an accessible and inexpensive process (Chapter 1).
In the TP process, germanium (Ge) is used as the nucleation layer of noble metallic thin films to prevent structural distortion and improve surface morphology. The developed Ge-assisted transfer printing (GTP) demonstrates its feasibility transferring sub-100 nm features with up to 50 nm thickness in a centimeter scale. The GTP is also capable of transferring arbitrary metallic nano-apertures with minimal pattern distortion, providing relatively less expensive, simpler, and scalable manufacturing (Chapter 2).
NIL is employed to fabricate the double-layered chiral metasurface for polarimetric imaging applications. The developed NIL process provides multi-functionalities with a single NIL, i.e., spacing layer, planarized surface, and formation of dielectric gratings, respectively, which significantly reduces fabrication processing time and potential cost by eliminating several steps in the conventional fabrication process. During the integration of two metasurfaces, the Moiré fringe based alignment method is employed to accomplish the alignment accuracy of less than 200 nm in both x- and y-directions, which is superior to conventional photolithography. The dramatically improved optical performance, e.g., highly improved circular polarization extinction ratio (CPER), is also achieved with the developed NIL process (Chapter 3).
ContributorsChoi, Shinhyuk (Author) / Wang, Chao (Thesis advisor) / Yu, Hongbin (Committee member) / Holman, Zachary (Committee member) / Hwa, Yoon (Committee member) / Arizona State University (Publisher)
Created2023