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Description
In this work, I worked on the synthesis and characterization of nanowires and belts, grown using different materials, in Chemical Vapor Deposition (CVD) system with catalytic growth method. Through this thesis, I utilized the Photoluminescence (PL), Secondary Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray diffraction (XRD) analyses to find out the properties of Erbium Chloride Silicate (ECS) and two segment CdS-CdSe samples. In the first part of my research, growth of very new material, Erbium Chloride Silicate (ECS), in form of core/shell Si/ECS and pure ECS nanowires, was demonstrated. This new material has very fascinating properties for new Si based photonic devices. The Erbium density in those nanowires is which is very high value compared to the other Erbium doped materials. It was shown that the luminescence peaks of ECS nanowires are very sharp and stronger than their counterparts. Furthermore, both PL and XRD peaks get sharper and stronger as growth temperature increases and this shows that crystalline quality of ECS nanowires gets better with higher temperature. In the second part, I did a very detail research for growing two segment axial nanowires or radial belts and report that the structure type mostly depends on the growth temperature. Since our final step is to create white light LEDs using single axial nanowires which have three different regions grown with distinct materials and give red, green and blue colors simultaneously, we worked on growing CdS-CdSe nanowires or belts for the first step of our aim. Those products were successfully grown and they gave two luminescence peaks with maximum 160 nm wavelength separation depending on the growth conditions. It was observed that products become more likely belt once the substrate temperature increases. Also, dominance between VLS and VS is very critical to determine the shape of the products and the substitution of CdS by CdSe is very effective; hence, CdSe growth time should be chosen accordingly. However, it was shown two segmented products can be synthesized by picking the right conditions and with very careful analyses. We also demonstrated that simultaneous two colors lasing from a single segmented belt structures is possible with strong enough-pumping-power.
ContributorsTurkdogan, Sunay (Author) / Ning, Cun-Zheng (Thesis advisor) / Tao, Meng (Committee member) / Yu, Hongbin (Committee member) / Arizona State University (Publisher)
Created2012
Description
A major obstacle to sustainable solar technologies is end-of-life solar modules. In this thesis, a recycling process is proposed for crystalline-Si solar modules. It is a three-step process to break down Si modules and recover various materials. Over 95% of a module by weight can be recovered with this process. Two new technologies are demonstrated to enable the proposed recycling process. One is sequential electrowinning which allows multiple metals to be recovered one by one from Si modules, Ag, Pb, Sn and Cu. The other is sheet resistance monitoring by the 4-point probe which maximizes the amount of solar-grade Si recovered from Si modules with high throughput. The purity of the recovered metals is above 99% and the recovery rate can achieve between 70~80%. The recovered Si meets the specifications for solar-grade Si and at least 91% of Si from c-Si solar cells can be recovered. The recovered Si and metals are new feedstocks to the solar industry and generate over $12/module in revenue. This revenue enables a profitable recycling business for Si modules without any government support. The chemicals for recycling are carefully selected to minimize their environmental impact and also the cost. A network for collecting end-of-life solar modules is proposed based on the current distribution network for solar modules to contain the collection cost. As a result, the proposed recycling process for c-Si modules is technically, environmentally and financially sustainable.
ContributorsHuang, Wenxi (Author) / Tao, Meng (Thesis advisor) / Alford, Terry (Committee member) / Sinha, Parikhit (Committee member) / Arizona State University (Publisher)
Created2018
Description
Photovoltaics (PV) is one of the promising options for maintaining sustainable energy supply because it is environmentally friendly, a non-polluting and low-maintenance energy source. Despite the many advantages of PV, solar energy currently accounts for only 1% of the global energy portfolio for electricity generation. This is because the cost of electricity from PV remains about a factor of two higher than the fossil fuel (10¢/kWh). Widely-used commercial methods employed to generate PV energy, such as silicon or thin film-based technologies, are still expensive as they are processed through vacuum-based techniques. Therefore, it is desirable to find an alternative method that is open-air and continuous process for the mass production of solar cells.
The objective of the research in this thesis is to develop low-cost spray pyrolysis technique to synthesize oxides thin films for applications in solar cells. Chapter 4 and 5 discuss spray-deposited dielectric oxides for their applications in Si solar cells. In Chapter 4, a successful deposition of Al2O3 is demonstrated using water as the solvent which ensures a lower cost and safer process environment. Optical, electrical, and structural properties of spray-deposited Al2O3 are investigated and compared to the industrial standard Atomic Layer Deposition (ALD) Al2O3/Plasma Enhanced Chemical Vapor Deposition (PECVD) SiNx stack, to reveal the suitability of spray-deposited Al2O3 for rear passivation and optical trapping in p-type Si Passivated Emitter and Rear Cell (PERC) solar cells. In Chapter 5, The possibility of using low-cost spray-deposited ZrO2 as the antireflection coating for Si solar cells is investigated. Optical, electrical and structural properties of spray-deposited ZrO2 films are studied and compared to the industrial standard antireflection coating PECVD SiNx. In Chapter 6, spray-deposited hematite Fe2O3 and sol-gel prepared anatase TiO2 thin films are sulfurized by annealing in H2S to investigate the band gap narrowing by sulfur doping and explore the possibility of using ternary semiconductors for their application as solar absorbers.
The objective of the research in this thesis is to develop low-cost spray pyrolysis technique to synthesize oxides thin films for applications in solar cells. Chapter 4 and 5 discuss spray-deposited dielectric oxides for their applications in Si solar cells. In Chapter 4, a successful deposition of Al2O3 is demonstrated using water as the solvent which ensures a lower cost and safer process environment. Optical, electrical, and structural properties of spray-deposited Al2O3 are investigated and compared to the industrial standard Atomic Layer Deposition (ALD) Al2O3/Plasma Enhanced Chemical Vapor Deposition (PECVD) SiNx stack, to reveal the suitability of spray-deposited Al2O3 for rear passivation and optical trapping in p-type Si Passivated Emitter and Rear Cell (PERC) solar cells. In Chapter 5, The possibility of using low-cost spray-deposited ZrO2 as the antireflection coating for Si solar cells is investigated. Optical, electrical and structural properties of spray-deposited ZrO2 films are studied and compared to the industrial standard antireflection coating PECVD SiNx. In Chapter 6, spray-deposited hematite Fe2O3 and sol-gel prepared anatase TiO2 thin films are sulfurized by annealing in H2S to investigate the band gap narrowing by sulfur doping and explore the possibility of using ternary semiconductors for their application as solar absorbers.
ContributorsShin, Woo Jung (Author) / Tao, Meng (Thesis advisor) / Goryll, Michael (Committee member) / Wang, Qing Hua (Committee member) / Arizona State University (Publisher)
Created2019
Description
The silicon-based solar cell has been extensively deployed in photovoltaic industry and plays an important role in renewable energy industries. A more energy-efficient, environment-harmless and eco-friendly silicon production technique is required for price-competitive solar energy harvesting. Silicon electrorefining in molten salt is promising for the ultrapure solar-grade Si production. To avoid using highly corrosive fluoride salt, CaCl2-based salt is widely employed for silicon electroreduction. For Si electroreduction in CaCl2-based salt, CaO is usually added to enhance the solubility of SiO2. However, the existence of oxygen in molten salt could result in system corrosion, anode passivation and the co-deposition of secondary phases such as CaSiO3 and SiO2 at the cathode. This research focuses on the development of reusable oxygen-free CaCl2-based molten salt for solar-grade silicon electrorefining. A new multi-potential electropurification process has been proposed and proven to be more effective in impurities removal. The as-received salt and the salt after electrorefining have been electropurified. The inductively-coupled plasma mass spectrometry and cyclic voltammetry have been utilized to determine the impurities removal of electropurification. The salt after silicon electrorefining has been regenerated to its original purity level before by the multi-potential electropurification process, demonstrating the feasibility of a reusable salt by electropurification. In an oxygen-free CaCl2-based salt without silicon precursor, the silicon dissolved from the silicon anode can be successfully deposited at the cathode. The silicon anode has been operated for more than 50 hours without passivation in the oxygen-free system. Silicon ions start to be deposited after 0.17 g of silicon has been dissolved into the salt from the silicon anode. A 180 µm deposit with a silver-luster surface was obtained at the cathode. The main impurities in the silicon anode such as aluminum, iron and titanium were not found in the silicon deposits. No oxygen-containing secondary phases are detected in the silicon deposits. These results confirm the feasibility of silicon electrorefining in the oxygen-free CaCl2-based salt.
ContributorsTseng, Mao-Feng (Author) / Tao, Meng (Thesis advisor) / Kannan, Arunachala Mada (Committee member) / Mu, Linqin (Committee member) / Goryll, Michael (Committee member) / Arizona State University (Publisher)
Created2023