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Calcium Film Based Testing of Edge-Seal Materials for Photovoltaic Applications (Presentation)

Description: Because of the sensitivity of some photovoltaic devices to moisture-induced corrosion, they are packaged using impermeable front- and back-sheets with an edge seal to prevent moisture ingress. Evaluation of edge seal materials can be difficult because of the low permeation rates involved and/or non-Fickian behavior. Here, using a Ca film deposited on a glass substrate, we demonstrate the evaluation of edge seal materials in a manner that effectively duplicates their use in a photovoltaic application and compare the results with standard methods for measuring water vapor transport. We demonstrate how moisture permeation data from polymer films can be used to estimate moisture ingress rates and compare the results of these two methods. Encapsulant materials were also evaluated for comparison and to highlight the need for edge seals. Of the materials studied, dessicant-filled polyisobutene materials demonstrate by far the best potential to keep moisture out for a 20 to 30 year lifetime.
Date: April 1, 2011
Creator: Kempe, M.; Dameron, A. & Reese, M.
Partner: UNT Libraries Government Documents Department

Calcium Based Test Method for Evaluation of Photovoltaic Edge-Seal Materials (Presentation)

Description: Because of the sensitivity of some photovoltaic devices to moisture-induced corrosion, they are packaged using impermeable front- and back-sheets with an edge seal to prevent moisture ingress. Evaluation of edge seal materials can be difficult because of the low permeation rates involved and/or non-Fickian behavior. Here, using a Ca film deposited on a glass substrate, we demonstrate the evaluation of edge seal materials in a manner that effectively duplicates their use in a photovoltaic application and compare the results with standard methods for measuring water vapor transport. We demonstrate how moisture permeation data from polymer films can be used to estimate moisture ingress rates and compare the results of these two methods. Encapsulant materials were also evaluated for comparison and to highlight the need for edge seals. Of the materials studied, dessicant-filled polyisobutene materials demonstrate by far the best potential to keep moisture out for a 20 to 30 year lifetime.
Date: February 1, 2011
Creator: Kempe, M.; Dameron, A. & Reese, M.
Partner: UNT Libraries Government Documents Department

Evaluation and Modeling of Edge-Seal Materials for Photovoltaic Applications

Description: Because of the sensitivity of some photovoltaic devices to moisture-induced corrosion, they are packaged using impermeable front- and back-sheets along with an edge seal to prevent moisture ingress. Evaluation of edge seal materials can be difficult because of the low permeation rates involved and/or non-Fickian behavior. Here, using a Ca film deposited on a glass substrate, we demonstrate the evaluation of edge seal materials in a manner that effectively duplicates their use in a photovoltaic application and compare the results with standard methods for measuring water vapor transport. We demonstrate how moisture permeation data from polymer films can be used to estimate moisture ingress rates and compare the results of these two methods. Encapsulant materials were also evaluated for comparison and to highlight the need for edge seals. Of the materials studied, desiccant filled polyisobutylene materials demonstrate by far the best potential to keep moisture out for a 20 to 30 year lifetime.
Date: February 1, 2011
Creator: Kempe, M. D.; Dameron, A. A.; Moricone, T. J. & Reese, M. O.
Partner: UNT Libraries Government Documents Department

Predicting the Performance of Edge Seal Materials for PV (Presentation)

Description: Edge seal materials were evaluated using a 100-nm film of Ca deposited on glass and laminated to another glass substrate. As moisture penetrates the package it converts the Ca metal to transparent CaOH2 giving a clear indication of the depth to which moisture has entered. Using this method, we have exposed test samples to a variety of temperature and humidity conditions ranging from 45C and 10% RH up to 85C and 85% RH, to ultraviolet radiation and to mechanical stress. We are able to show that edge seal materials are capable of keeping moisture away from sensitive cell materials for the life of a module.
Date: March 1, 2012
Creator: Kempe, M.; Panchagade, D.; Dameron, A. & Reese, M.
Partner: UNT Libraries Government Documents Department

Do the Defects Make it Work? Defect Engineering in ..pi.. - Conjugated Polymer Films and Their Solar Cells (Presentation)

Description: The summaries of this report are: (1) charged defects produce 10{sup 15}-10{sup 17} cm{sup -3} free carriers; (2) treatment with nucleophiles decreases p{sub f} and {sigma} while treatment with electrophiles does not change p{sub f} but increases {sigma}; (3) both treatments increase {mu}{sub p}, L{sub ex} and stability against photo-degradation; (4) charged defects can improve OPV by increasing conductivity and creating interfacial electric fields but they hurt {mu}{sub p}, L{sub ex} and chemical stability; and (5) a better way--synthesize materials without covalent defects and dope with purposely added, bound dopants.
Date: May 1, 2008
Creator: Gregg, B. A.; Wang, D.; Reese, M. O. & Kopidakis, N.
Partner: UNT Libraries Government Documents Department

Do the Defects Make It Work? Defect Engineering in Pi-Conjugated Polymers and Their Solar Cells: Preprint

Description: The charged defect density in common pi-conjugated polymers such as poly(3-hexylthiophene), P3HT, is around 1018 cm-3. Despite, or perhaps because of, this huge defect density, bulk heterojunction solar cells made from these polymers and a C60 derivative such as PCBM exhibit some of the highest efficiencies (~5%) yet obtained in solid state organic photovoltaic cells. We discuss defects in molecular organic semiconductors and in pi-conjugated polymers. These defects can be grouped in two categories, covalent and noncovalent. Somewhat analogous to treating amorphous silicon with hydrogen, we introduce chemical methods to modify the density and charge of the covalent defects in P3HT by treating it with electrophiles such as dimethyl sulfate and nucleophiles such as sodium methoxide. The effects of these treatments on the electrical and photovoltaic properties and stability of organic PV cells is discussed in terms of the change in the number and chemical properties of the defects. Finally, we address the question of whether the efficiency of OPV cells requires the presence of these defects which function as adventitious p-type dopants. Their presence relieves the resistance limitations usually encountered in cleaner organic semiconductors and can create built-in electric fields at junctions.
Date: May 1, 2008
Creator: Wang, D.; Reese, M.; N., Kopidakis & Gregg, B. A.
Partner: UNT Libraries Government Documents Department

Transparent Conducting Contacts Based on Zinc Oxide Substitutionally Doped with Gallium: Preprint

Description: Transparent conducting oxides (TCOs) are a critical element in photovoltaic devices. This paper describes research on Ga:ZnO (a TCO candidate) using a high-throughput combinatorial approach.
Date: May 1, 2008
Creator: Gorrie, C. W.; Reese, M.; Perkins, J. D.; Alleman, J. L.; S., Dabney M.; To, B. et al.
Partner: UNT Libraries Government Documents Department

Overcoming Degradation in Organic Photovoltaics: Illuminating the Role of Fullerene Functionalization: Preprint

Description: Photobleaching rates are investigated for thin films of poly(3-hexylthiophene) (P3HT) blends employing either an indene-C60 bisadduct (ICBA) or [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the electron acceptor. Relative to the bisindene, PCBM significantly enhances resistance to photobleaching of the P3HT donor polymer. We tentatively attribute a decrease in the charge transfer rate as the mechanism responsible for the more rapid photobleaching in the sample containing the bisindene adduct. In order to elucidate the influence of the photobleaching rate on the initial performance of unencapsulated devices, we also monitored the time-dependent behavior for P3HT:fullerene inverted devices. Under conditions of constant illumination, we observe essentially identical behavior in device performance parameters regardless of the energy levels of the electron acceptor. We conclude that over the time frame measured for these devices, the primary degradation mechanism of the active layer is independent of the electron acceptor, despite the enhanced tolerance to photobleaching it may impart to the donor material.
Date: July 1, 2011
Creator: Lloyd, M. T.; Garcia, A.; Berry, J. J.; Reese, M. O.; Ginley, D. S. & Olson, D. C.
Partner: UNT Libraries Government Documents Department

Short-Term Metal/Organic Interface Stability Investigations of Organic Photovoltaic Devices: Preprint

Description: This paper addresses one source of degradation in OPV devices: the metal/organic interface. The basic approach was to study the completed device stability vs. the stability of the organic film itself as shown in subsequent devices fabricated from the films.
Date: May 1, 2008
Creator: Reese, M. O.; Morfa, A. J.; White, M. S.; Kopidakis, N.; Shaheen, S. E.; Rumbles, G. et al.
Partner: UNT Libraries Government Documents Department

Understanding Degradation Pathways in Organic Photovoltaics (Poster)

Description: Organic Photovoltaics (OPVs) recently attained power conversion efficiencies that are of interest for commercial production. Consequently, one of the most important unsolved issues facing a new industry is understanding what governs lifetime in organic devices and discovering solutions to mitigate degradation mechanisms. Historically, the active organic components are considered vulnerable to photo-oxidation and represent the primary degradation channel. However, we present several (shelf life and light soaking) studies pointing the relative stability of the active layers and instabilities in commonly used electrode materials. We show that engineering of the hole/electron layer at the electrode can lead to environmentally stable devices even without encapsulation.
Date: February 1, 2011
Creator: Lloyd, M. T.; Olson, D. C.; Garcia, A.; Kauvar, I.; Kopidakis, N.; Reese, M. O. et al.
Partner: UNT Libraries Government Documents Department