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- Creators: Green, Matthew
Description
Ethylene vinyl acetate (EVA) is the most commonly used encapsulant in photovoltaic modules. However, EVA degrades over time and causes performance losses in PV system. Therefore, EVA degradation is a matter of concern from a durability point of view.
This work compares EVA encapsulant degradation in glass/backsheet and glass/glass field-aged PV modules. EVA was extracted from three field-aged modules (two glass/backsheet and one glass/glass modules) from three different manufacturers from various regions (cell edges, cell centers, and non-cell region) from each module based on their visual and UV Fluorescence images. Characterization techniques such as I-V measurements, Colorimetry, Different Scanning Calorimetry, Thermogravimetric Analysis, Raman spectroscopy, and Fourier Transform Infrared Spectroscopy were performed on EVA samples.
The intensity of EVA discoloration was quantified using colorimetric measurements. Module performance parameters like Isc and Pmax degradation rates were calculated from I-V measurements. Properties such as degree of crystallinity, vinyl acetate content and degree of crosslinking were calculated from DSC, TGA, and Raman measurements, respectively. Polyenes responsible for EVA browning were identified in FTIR spectra.
The results from the characterization techniques confirmed that when EVA undergoes degradation, crosslinking in EVA increases beyond 90% causing a decrease in the degree of crystallinity and an increase in vinyl acetate content of EVA. Presence of polyenes in FTIR spectra of degraded EVA confirmed the occurrence of Norrish II reaction. However, photobleaching occurred in glass/backsheet modules due to the breathable backsheet whereas no photobleaching occurred in glass/glass modules because they were hermetically sealed. Hence, the yellowness index along with the Isc and Pmax degradation rates of EVA in glass/glass module is higher than that in glass/backsheet modules.
The results implied that more acetic acid was produced in the non-cell region due to its double layer of EVA compared to the front EVA from cell region. But, since glass/glass module is hermetically sealed, acetic acid gets entrapped inside the module further accelerating EVA degradation whereas it diffuses out through backsheet in glass/backsheet modules. Hence, it can be said that EVA might be a good encapsulant for glass/backsheet modules, but the same cannot be said for glass/glass modules.
This work compares EVA encapsulant degradation in glass/backsheet and glass/glass field-aged PV modules. EVA was extracted from three field-aged modules (two glass/backsheet and one glass/glass modules) from three different manufacturers from various regions (cell edges, cell centers, and non-cell region) from each module based on their visual and UV Fluorescence images. Characterization techniques such as I-V measurements, Colorimetry, Different Scanning Calorimetry, Thermogravimetric Analysis, Raman spectroscopy, and Fourier Transform Infrared Spectroscopy were performed on EVA samples.
The intensity of EVA discoloration was quantified using colorimetric measurements. Module performance parameters like Isc and Pmax degradation rates were calculated from I-V measurements. Properties such as degree of crystallinity, vinyl acetate content and degree of crosslinking were calculated from DSC, TGA, and Raman measurements, respectively. Polyenes responsible for EVA browning were identified in FTIR spectra.
The results from the characterization techniques confirmed that when EVA undergoes degradation, crosslinking in EVA increases beyond 90% causing a decrease in the degree of crystallinity and an increase in vinyl acetate content of EVA. Presence of polyenes in FTIR spectra of degraded EVA confirmed the occurrence of Norrish II reaction. However, photobleaching occurred in glass/backsheet modules due to the breathable backsheet whereas no photobleaching occurred in glass/glass modules because they were hermetically sealed. Hence, the yellowness index along with the Isc and Pmax degradation rates of EVA in glass/glass module is higher than that in glass/backsheet modules.
The results implied that more acetic acid was produced in the non-cell region due to its double layer of EVA compared to the front EVA from cell region. But, since glass/glass module is hermetically sealed, acetic acid gets entrapped inside the module further accelerating EVA degradation whereas it diffuses out through backsheet in glass/backsheet modules. Hence, it can be said that EVA might be a good encapsulant for glass/backsheet modules, but the same cannot be said for glass/glass modules.
ContributorsPatel, Aesha Parimalbhai (Author) / Tamizhmani, Govindasamy (Thesis advisor) / Green, Matthew (Committee member) / Mu, Bin (Committee member) / Arizona State University (Publisher)
Created2018
Description
A new class of layered materials called the transition metal trichalcogenides (TMTCs) exhibit strong anisotropic properties due to their quasi-1D nature. These 2D materials are composed of chain-like structures which are weakly bound to form planar sheets with highly directional properties. The vibrational properties of three materials from the TMTC family, specifically TiS3, ZrS3, and HfS3, are relatively unknown and studies performed in this work elucidates the origin of their Raman characteristics. The crystals were synthesized through chemical vapor transport prior to mechanical exfoliation onto Si/SiO¬2 substrates. XRD, AFM, and Raman spectroscopy were used to determine the crystallinity, thickness, and chemical signature of the exfoliated crystals. Vibrational modes and anisotropic polarization are investigated through density functional theory calculations and angle-resolved Raman spectroscopy. Particular Raman modes are explored in order to correlate select peaks to the b-axis crystalline direction. Mode III vibrations for TiS3, ZrS3, and HfS3 are shared between each material and serves as a unique identifier of the crystalline orientation in MX3 materials. Similar angle-resolved Raman studies were conducted on the novel Nb0.5Ti0.5S3 alloy material grown through chemical vapor transport. Results show that the anisotropy direction is more difficult to determine due to the randomization of quasi-1D chains caused by defects that are common in 2D alloys. This work provides a fundamental understanding of the vibrational properties of various TMTC materials which is needed to realize applications in direction dependent polarization and linear dichroism.
ContributorsKong, Wilson (Author) / Tongay, Sefaattin (Thesis advisor) / Wang, Liping (Committee member) / Green, Matthew (Committee member) / Arizona State University (Publisher)
Created2017
Description
This is a two-part thesis assessing the long-term reliability of photovoltaic modules.
Part 1: Manufacturing dependent reliability - Adapting FMECA for quality control in PV module manufacturing
This part is aimed at introducing a statistical tool in quality assessments in PV module manufacturing. Developed jointly by ASU-PRL and Clean Energy Associates, this work adapts the Failure Mode Effect and Criticality Analysis (FMECA, IEC 60812) to quantify the impact of failure modes observed at the time of manufacturing. The method was developed through analysis of nearly 9000 modules at the pre-shipment evaluation stage in module manufacturing facilities across south east Asia. Numerous projects were analyzed to generate RPN (Risk Priority Number) scores for projects. In this manner, it was possibly to quantitatively assess the risk being carried the project at the time of shipment of modules. The objective of this work was to develop a benchmarking system that would allow for accurate quantitative estimations of risk mitigation and project bankability.
Part 2: Climate dependent reliability - Activation energy determination for climate specific degradation modes
This work attempts to model the parameter (Isc or Rs) degradation rate of modules as a function of the climatic parameters (i.e. temperature, relative humidity and ultraviolet radiation) at the site. The objective of this work was to look beyond the power degradation rate and model based on the performance parameter directly affected by the degradation mode under investigation (encapsulant browning or IMS degradation of solder bonds). Different physical models were tested and validated through comparing the activation energy obtained for each degradation mode. It was concluded that, for the degradation of the solder bonds within the module, the Pecks equation (function of temperature and relative humidity) modelled with Rs increase was the best fit; the activation energy ranging from 0.4 – 0.7 eV based on the climate type. For encapsulant browning, the Modified Arrhenius equation (function of temperature and UV) seemed to be the best fit presently, yielding an activation energy of 0.3 eV. The work was concluded by suggesting possible modifications to the models based on degradation pathways unaccounted for in the present work.
Part 1: Manufacturing dependent reliability - Adapting FMECA for quality control in PV module manufacturing
This part is aimed at introducing a statistical tool in quality assessments in PV module manufacturing. Developed jointly by ASU-PRL and Clean Energy Associates, this work adapts the Failure Mode Effect and Criticality Analysis (FMECA, IEC 60812) to quantify the impact of failure modes observed at the time of manufacturing. The method was developed through analysis of nearly 9000 modules at the pre-shipment evaluation stage in module manufacturing facilities across south east Asia. Numerous projects were analyzed to generate RPN (Risk Priority Number) scores for projects. In this manner, it was possibly to quantitatively assess the risk being carried the project at the time of shipment of modules. The objective of this work was to develop a benchmarking system that would allow for accurate quantitative estimations of risk mitigation and project bankability.
Part 2: Climate dependent reliability - Activation energy determination for climate specific degradation modes
This work attempts to model the parameter (Isc or Rs) degradation rate of modules as a function of the climatic parameters (i.e. temperature, relative humidity and ultraviolet radiation) at the site. The objective of this work was to look beyond the power degradation rate and model based on the performance parameter directly affected by the degradation mode under investigation (encapsulant browning or IMS degradation of solder bonds). Different physical models were tested and validated through comparing the activation energy obtained for each degradation mode. It was concluded that, for the degradation of the solder bonds within the module, the Pecks equation (function of temperature and relative humidity) modelled with Rs increase was the best fit; the activation energy ranging from 0.4 – 0.7 eV based on the climate type. For encapsulant browning, the Modified Arrhenius equation (function of temperature and UV) seemed to be the best fit presently, yielding an activation energy of 0.3 eV. The work was concluded by suggesting possible modifications to the models based on degradation pathways unaccounted for in the present work.
ContributorsPore, Shantanu (Author) / Tamizhmani, Govindasamy (Thesis advisor) / Green, Matthew (Thesis advisor) / Srinivasan, Devrajan (Committee member) / Arizona State University (Publisher)
Created2017
Description
More recently there have been a tremendous advancement in theoretical studies showing remarkable properties that could be exploited from transition metal dichalcogenide (TMDC) Janus crystals through various applications. These Janus crystals are having a proven intrinsic electrical field due to breaking of out-of-plane inversion symmetry in a conventional TMDC when one of the chalcogenides atomic layer is being completely replaced by a layer of different chalcogen element. However, due to lack of accurate processing control at nanometer scales, key for creating a highly crystalline Janus structure has not yet been familiarized. Thus, experimental characterization and implication of these Janus crystals are still in a state of stagnation. This work presents a new advanced methodology that could prove to be highly efficient and effective for selective replacement of top layer atomic sites at room temperature conditions.
This is specifically more focused on proving an easy repeatability for replacement of top atomic layer chalcogenide from a parent structure of already grown TMDC monolayer (via CVD) by a post plasma processing technique. Though this developed technique is not limited to only chalcogen atom replacement but can be extended to any type of surface functionalization requirements.
Basic characterization has been performed on the Janus crystal of SeMoS and SeWS where, creation and characterization of SeWS has been done for the very first time, evidencing a repeatable nature of the developed methodology.
This is specifically more focused on proving an easy repeatability for replacement of top atomic layer chalcogenide from a parent structure of already grown TMDC monolayer (via CVD) by a post plasma processing technique. Though this developed technique is not limited to only chalcogen atom replacement but can be extended to any type of surface functionalization requirements.
Basic characterization has been performed on the Janus crystal of SeMoS and SeWS where, creation and characterization of SeWS has been done for the very first time, evidencing a repeatable nature of the developed methodology.
ContributorsTrivedi, Dipesh (Author) / Tongay, Sefaattin (Thesis advisor) / Green, Matthew (Committee member) / Zhuang, Houlong (Committee member) / Arizona State University (Publisher)
Created2019
Description
Two-dimensional quantum materials have garnered increasing interest in a wide
variety of applications due to their promising optical and electronic properties. These
quantum materials are highly anticipated to make transformative quantum sensors and
biosensors. Biosensors are currently considered among one of the most promising
solutions to a wide variety of biomedical and environmental problems including highly
sensitive and selective detection of difficult pathogens, toxins, and biomolecules.
However, scientists face enormous challenges in achieving these goals with current
technologies. Quantum biosensors can have detection with extraordinary sensitivity and
selectivity through manipulation of their quantum states, offering extraordinary properties
that cannot be attained with traditional materials. These quantum materials are anticipated
to make significant impact in the detection, diagnosis, and treatment of many diseases.
Despite the exciting promise of these cutting-edge technologies, it is largely
unknown what the inherent toxicity and biocompatibility of two-dimensional (2D)
materials are. Studies are greatly needed to lay the foundation for understanding the
interactions between quantum materials and biosystems. This work introduces a new
method to continuously monitor the cell proliferation and toxicity behavior of 2D
materials. The cell viability and toxicity measurements coupled with Live/Dead
fluorescence imaging suggest the biocompatibility of crystalline MoS2 and MoSSe
monolayers and the significantly-reduced cellular growth of defected MoTe2 thin films
and exfoliated MoS2 nanosheets. Results show the exciting potential of incorporating
kinetic cell viability data of 2D materials with other assay tools to further fundamental
understanding of 2D material biocompatibility.
variety of applications due to their promising optical and electronic properties. These
quantum materials are highly anticipated to make transformative quantum sensors and
biosensors. Biosensors are currently considered among one of the most promising
solutions to a wide variety of biomedical and environmental problems including highly
sensitive and selective detection of difficult pathogens, toxins, and biomolecules.
However, scientists face enormous challenges in achieving these goals with current
technologies. Quantum biosensors can have detection with extraordinary sensitivity and
selectivity through manipulation of their quantum states, offering extraordinary properties
that cannot be attained with traditional materials. These quantum materials are anticipated
to make significant impact in the detection, diagnosis, and treatment of many diseases.
Despite the exciting promise of these cutting-edge technologies, it is largely
unknown what the inherent toxicity and biocompatibility of two-dimensional (2D)
materials are. Studies are greatly needed to lay the foundation for understanding the
interactions between quantum materials and biosystems. This work introduces a new
method to continuously monitor the cell proliferation and toxicity behavior of 2D
materials. The cell viability and toxicity measurements coupled with Live/Dead
fluorescence imaging suggest the biocompatibility of crystalline MoS2 and MoSSe
monolayers and the significantly-reduced cellular growth of defected MoTe2 thin films
and exfoliated MoS2 nanosheets. Results show the exciting potential of incorporating
kinetic cell viability data of 2D materials with other assay tools to further fundamental
understanding of 2D material biocompatibility.
ContributorsTran, Michael, Ph.D (Author) / Tongay, Sefaattin (Thesis advisor) / Green, Matthew (Thesis advisor) / Muhich, Christopher (Committee member) / Arizona State University (Publisher)
Created2019