Matching Items (7)
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- All Subjects: Membranes
- All Subjects: Semiconductors--Defects.
- Creators: Alford, Terry
- Creators: Durgun, Pinar Cay
Description
Recent technology advancements in photovoltaics have enabled crystalline silicon (c-Si) solar cells to establish outstanding photoconversion efficiency records. Remarkable progresses in research and development have been made both on the silicon feedstock quality as well as the technology required for surface passivation, the two dominant sources of performance loss via recombination of photo-generated charge carriers within advanced solar cell architectures.
As these two aspects of the solar cell framework improve, the need for a thorough analysis of their respective contribution under varying operation conditions has emerged along with challenges related to the lack of sensitivity of available characterization techniques. The main objective of my thesis work has been to establish a deep understanding of both “intrinsic” and “extrinsic” recombination processes that govern performance in high-quality silicon absorbers. By studying each recombination mechanism as a function of illumination and temperature, I strive to identify the lifetime limiting defects and propose a path to engineer the ultimate silicon solar cell.
This dissertation presents a detailed description of the experimental procedure required to deconvolute surface recombination contributions from bulk recombination contributions when performing lifetime spectroscopy analysis. This work proves that temperature- and injection-dependent lifetime spectroscopy (TIDLS) sensitivity can be extended to impurities concentrations down to 109 cm-3, orders of magnitude below any other characterization technique available today. A new method for the analysis of TIDLS data denominated Defect Parameters Contour Mapping (DPCM) is presented with the aim of providing a visual and intuitive tool to identify the lifetime limiting impurities in silicon material. Surface recombination velocity results are modelled by applying appropriate approaches from literature to our experimentally evaluated data, demonstrating for the first time their capability to interpret temperature-dependent data. In this way, several new results are obtained which solve long disputed aspects of surface passivation mechanisms. Finally, we experimentally evaluate the temperature-dependence of Auger lifetime and its impact on a theoretical intrinsically limited solar cell. These results decisively point to the need for a new Auger lifetime parameterization accounting for its temperature-dependence, which would in turn help understand the ultimate theoretical efficiency limit for a solar cell under real operation conditions.
As these two aspects of the solar cell framework improve, the need for a thorough analysis of their respective contribution under varying operation conditions has emerged along with challenges related to the lack of sensitivity of available characterization techniques. The main objective of my thesis work has been to establish a deep understanding of both “intrinsic” and “extrinsic” recombination processes that govern performance in high-quality silicon absorbers. By studying each recombination mechanism as a function of illumination and temperature, I strive to identify the lifetime limiting defects and propose a path to engineer the ultimate silicon solar cell.
This dissertation presents a detailed description of the experimental procedure required to deconvolute surface recombination contributions from bulk recombination contributions when performing lifetime spectroscopy analysis. This work proves that temperature- and injection-dependent lifetime spectroscopy (TIDLS) sensitivity can be extended to impurities concentrations down to 109 cm-3, orders of magnitude below any other characterization technique available today. A new method for the analysis of TIDLS data denominated Defect Parameters Contour Mapping (DPCM) is presented with the aim of providing a visual and intuitive tool to identify the lifetime limiting impurities in silicon material. Surface recombination velocity results are modelled by applying appropriate approaches from literature to our experimentally evaluated data, demonstrating for the first time their capability to interpret temperature-dependent data. In this way, several new results are obtained which solve long disputed aspects of surface passivation mechanisms. Finally, we experimentally evaluate the temperature-dependence of Auger lifetime and its impact on a theoretical intrinsically limited solar cell. These results decisively point to the need for a new Auger lifetime parameterization accounting for its temperature-dependence, which would in turn help understand the ultimate theoretical efficiency limit for a solar cell under real operation conditions.
ContributorsBernardini, Simone (Author) / Bertoni, Mariana I (Thesis advisor) / Coletti, Gianluca (Committee member) / Bowden, Stuart (Committee member) / Alford, Terry (Committee member) / Arizona State University (Publisher)
Created2018
Description
In this project, current-voltage (I-V) and Deep Level Transient Spectroscopy (DLTS) measurements are used to (a) characterize the electrical properties of Nb/p-type Si Schottky barriers, (b) identify the concentration and physical character of the electrically active defects present in the depletion region, and (c) use thermal processing to reduce the concentration or eliminate the defects. Barrier height determinations using temperature-dependent I-V measurements indicate that the barrier height decreases from 0.50 eV to 0.48 eV for anneals above 200 C. The electrically-active defect concentration measured using DLTS (deep level transient spectroscopy) drops markedly after anneals at 250 C.
A significant increase in leakage currents is almost always observed in near-ideal devices upon annealing. In contrast, non-ideal devices dominated by leakage currents annealed at 150 C to 250 C exhibit a significant decrease in such currents.
A significant increase in leakage currents is almost always observed in near-ideal devices upon annealing. In contrast, non-ideal devices dominated by leakage currents annealed at 150 C to 250 C exhibit a significant decrease in such currents.
ContributorsKrishna Murthy, Madhu (Author) / Newman, Nathan (Thesis advisor) / Goryll, Michael (Committee member) / Alford, Terry (Committee member) / Arizona State University (Publisher)
Created2018
Description
Global photovoltaic (PV) module installation in 2018 is estimated to exceed 100 GW, and crystalline Si (c-Si) solar cell-based modules have a share more than 90% of the global PV market. To reduce the social cost of PV electricity, further developments in reliability of solar panels are expected. These will lead to realize longer module lifetime and reduced levelized cost of energy. As many as 86 failure modes are observed in PV modules [1] and series resistance increase is one of the major durability issues of all. Series resistance constitutes emitter sheet resistance, metal-semiconductor contact resistance, and resistance across the metal-solder ribbon. Solder bond degradation at the cell interconnect is one of the primary causes for increase in series resistance, which is also considered to be an invisible defect [1]. Combination of intermetallic compounds (IMC) formation during soldering and their growth due to solid state diffusion over its lifetime result in formation of weak interfaces between the solar cell and the interconnect. Thermal cycling under regular operating conditions induce thermo-mechanical fatigue over these weak interfaces resulting in contact reduction or loss. Contact reduction or loss leads to increase in series resistance which further manifests into power and fill factor loss. The degree of intermixing of metallic interfaces and contact loss depends on climatic conditions as temperature and humidity (moisture ingression into the PV module laminate) play a vital role in reaction kinetics of these layers. Modules from Arizona and Florida served as a good sample set to analyze the effects of hot and humid climatic conditions respectively. The results obtained in the current thesis quantifies the thickness of IMC formation from SEM-EDS profiles, where similar modules obtained from different climatic conditions were compared. The results indicate the thickness of the IMC and detachment degree to be growing with age and operating temperatures of the module. This can be seen in CuxSny IMC which is thicker in the case of Arizona module. The results obtained from FL
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aged modules also show that humidity accelerates the formation of IMC as they showed thicker AgxSny layer and weak interconnect-contact interfaces as compared to Arizona modules. It is also shown that climatic conditions have different effects on rate at which CuxSny and AgxSny intermetallic compounds are formed.
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aged modules also show that humidity accelerates the formation of IMC as they showed thicker AgxSny layer and weak interconnect-contact interfaces as compared to Arizona modules. It is also shown that climatic conditions have different effects on rate at which CuxSny and AgxSny intermetallic compounds are formed.
ContributorsBuddha, Viswa Sai Pavan (Author) / Tamizhmani, Govindasamy (Thesis advisor) / Alford, Terry (Thesis advisor) / Srinivasan, Devarajan (Committee member) / Arizona State University (Publisher)
Created2018
Description
The recovery of biofuels permits renewable alternatives to present day fossil fuels that cause devastating effects on the planet. Pervaporation is a separation process that shows promise for the separation of ethanol from biologically fermentation broths. The performance of thin film composite membranes of polydimethylsiloxane (PDMS) and zeolite imidazolate frameworks (ZIF-71) dip coated onto a porous substrate are analyzed. Pervaporation performance factors of flux, separation factor and selectivity are measured for varying ZIF-71 loadings of pure PDMS, 5 wt%, 12.5 wt% and 25 wt% at 60 oC with a 2 wt% ethanol/water feed. The increase in ZIF-71 loadings increased the performance of PDMS to produce higher flux, higher separation factor and high selectivity than pure polymeric films.
ContributorsLau, Ching Yan (Author) / Lind, Mary Laura (Thesis director) / Durgun, Pinar Cay (Committee member) / Lively, Ryan (Committee member) / Barrett, The Honors College (Contributor) / School of International Letters and Cultures (Contributor) / Chemical Engineering Program (Contributor)
Created2014-05
Description
Metal-organic frameworks (MOFs) are a new set of porous materials comprised of metals or metal clusters bonded together in a coordination system by organic linkers. They are becoming popular for gas separations due to their abilities to be tailored toward specific applications. Zirconium MOFs in particular are known for their high stability under standard temperature and pressure due to the strength of the Zirconium-Oxygen coordination bond. However, the acid modulator needed to ensure long range order of the product also prevents complete linker deprotonation. This leads to a powder product that cannot easily be incorporated into continuous MOF membranes. This study therefore implemented a new bi-phase synthesis technique with a deprotonating agent to achieve intergrowth in UiO-66 membranes. Crystal intergrowth will allow for effective gas separations and future permeation testing. During experimentation, successful intergrown UiO-66 membranes were synthesized and characterized. The degree of intergrowth and crystal orientations varied with changing deprotonating agent concentration, modulator concentration, and ligand:modulator ratios. Further studies will focus on achieving the same results on porous substrates.
ContributorsClose, Emily Charlotte (Author) / Mu, Bin (Thesis director) / Shan, Bohan (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
One of the grand challenges of engineering is to provide access to clean water because it is predicted that by 2025 more than two thirds of the world’s population will face severe water shortages. To combat this global issue, our lab focuses on creating a novel composite membrane to recover potable water from waste. For use as the water-selective component in this membrane design Linde Type A zeolites were synthesized for optimal size without the use of a template. Current template-free synthesis of zeolite LTA produces particles that are too large for our application therefore the particle size was reduced in this study to reduce fouling of the membrane while also investigating the nanoparticle synthesis mechanisms. The time and temperature of the reaction and the aging of the precursor gel were systematically modified and observed to determine the optimal conditions for producing the particles. Scanning electron microscopy, x-ray diffraction, and energy dispersive x-ray analysis were used for characterization. Sub-micron sized particles were synthesized at 2 weeks aging time at -8°C with an average size of 0.6 micrometers, a size suitable for our membrane. There is a limit to the posterity and uniformity of particles produced from modifying the reaction time and temperature. All results follow general crystallization theory. Longer aging produced smaller particles, consistent with nucleation theory. Spinodal decomposition is predicted to affect nucleation clustering during aging due to the temperature scheme. Efforts will be made to shorten the effective aging time and these particles will eventually be incorporated into our mixed matrix osmosis membrane.
ContributorsKing, Julia Ann (Author) / Lind, Mary Laura (Thesis director) / Durgun, Pinar Cay (Committee member) / Chemical Engineering Program (Contributor) / Materials Science and Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
ABSTRACT
Large-pore metal-organic framework (MOF) membranes offer potential in a number of gas and liquid separations due to their wide and selective adsorption capacities. A key characteristic of a number of MOF and zeolitic imidazolate framework (ZIF) membranes is their highly selective adsorption capacities for CO2. These membranes offer very tangible potential to separate CO2 in a wide array of industrially relevant separation processes, such as the separation from CO2 in flue gas emissions, as well as the sweetening of methane.
By virtue of this, the purpose of this dissertation is to synthesize and characterize two linear large-pore MOF membranes, MOF-5 and ZIF-68, and to study their gas separation properties in binary mixtures of CO¬2/N2 and CO2/CH4. The three main objectives researched are as follows. The first is to study the pervaporation behavior and stability of MOF-5; this is imperative because although MOF-5 exhibits desirable adsorption and separation characteristics, it is very unstable in atmospheric conditions. In determining its stability and behavior in pervaporation, this material can be utilized in conditions wherein atmospheric levels of moisture can be avoided. The second objective is to synthesize, optimize and characterize a linear, more stable MOF membrane, ZIF-68. The final objective is to study in tandem the high-pressure gas separation behavior of MOF-5 and ZIF-68 in binary gas systems of both CO2/N2 and CO2/CH4.
Continuous ZIF-68 membranes were synthesized via the reactive seeding method and the modified reactive seeding method. These membranes, as with the MOF-5 membranes synthesized herein, both showed adherence to Knudsen diffusion, indicating limited defects. Organic solvent experiments indicated that MOF-5 and ZIF-68 were stable in a variety of organic solvents, but both showed reductions in permeation flux of the tested molecules. These reductions were attributed to fouling and found to be cumulative up until a saturation of available bonding sites for molecules was reached and stable pervaporation permeances were reached for both. Gas separation behavior for MOF-5 showed direct dependence on the CO2 partial pressure and the overall feed pressure, while ZIF-68 did not show similar behavior. Differences in separation behavior are attributable to orientation of the ZIF-68 membranes.
Large-pore metal-organic framework (MOF) membranes offer potential in a number of gas and liquid separations due to their wide and selective adsorption capacities. A key characteristic of a number of MOF and zeolitic imidazolate framework (ZIF) membranes is their highly selective adsorption capacities for CO2. These membranes offer very tangible potential to separate CO2 in a wide array of industrially relevant separation processes, such as the separation from CO2 in flue gas emissions, as well as the sweetening of methane.
By virtue of this, the purpose of this dissertation is to synthesize and characterize two linear large-pore MOF membranes, MOF-5 and ZIF-68, and to study their gas separation properties in binary mixtures of CO¬2/N2 and CO2/CH4. The three main objectives researched are as follows. The first is to study the pervaporation behavior and stability of MOF-5; this is imperative because although MOF-5 exhibits desirable adsorption and separation characteristics, it is very unstable in atmospheric conditions. In determining its stability and behavior in pervaporation, this material can be utilized in conditions wherein atmospheric levels of moisture can be avoided. The second objective is to synthesize, optimize and characterize a linear, more stable MOF membrane, ZIF-68. The final objective is to study in tandem the high-pressure gas separation behavior of MOF-5 and ZIF-68 in binary gas systems of both CO2/N2 and CO2/CH4.
Continuous ZIF-68 membranes were synthesized via the reactive seeding method and the modified reactive seeding method. These membranes, as with the MOF-5 membranes synthesized herein, both showed adherence to Knudsen diffusion, indicating limited defects. Organic solvent experiments indicated that MOF-5 and ZIF-68 were stable in a variety of organic solvents, but both showed reductions in permeation flux of the tested molecules. These reductions were attributed to fouling and found to be cumulative up until a saturation of available bonding sites for molecules was reached and stable pervaporation permeances were reached for both. Gas separation behavior for MOF-5 showed direct dependence on the CO2 partial pressure and the overall feed pressure, while ZIF-68 did not show similar behavior. Differences in separation behavior are attributable to orientation of the ZIF-68 membranes.
ContributorsKasik, Alexandra Marie (Author) / Lin, Jerry (Thesis advisor) / Tasooji, Amaneh (Committee member) / Alford, Terry (Committee member) / Arizona State University (Publisher)
Created2015