Performance and durability of HgI_2 X-ray detectors for space missions

Considerable progress has been achieved in HgI_2 detector fabrication technology and amplification electronics. An energy resolution of 198 eV (full width at half maximum) has been obtained for the Mn K_α line of 5.9 keV in a practical X-ray probe without the use of cryogenic cooling. Detectors prepared with Parylene-C encapsulation have demonstrated perfect reliability in two-year tests under high vacuum and temperature and bias cycling. Other HgI_2 detectors have been used to demonstrate proton-radiation-damage resistance to levels of 10^(12) protons/cm^2 at 10.7 MeV. It is concluded that HgI_2 detectors are suitable for the ordinary requirements of energy dispersive detectors in X-ray spectroscopy systems

Stability diagnostics for thin-film photovoltaic modules

Photovoltaic (PV) modules create electricity from solar radiation by converting photon energy to electrical potential energy. The use of photovoltaic electricity is growing rapidly particularly in building-integrated, grid-connected applications. The useful lifetime of PV modules is an important determinant of the competitiveness of PV electricity. Lifetime improvement and prediction requires detailed information on degradation mechanisms in the field and in accelerated aging tests. In this thesis, new methods for studying and predicting the stability of thin-film PV modules have been developed. Stability is a greater challenge for thin-film devices than for established PV technologies, and good stability diagnostics are therefore crucial for improvements in thin-film device lifetime. The diagnostics developed in this thesis focused on two areas of lifetime research. The first was the study of water transport in photovoltaic module encapsulants. It was shown that a TiO2 film of micrometer thickness can be used as a sensor structure to measure water transport in the encapsulant with high accuracy without affecting the transport process. The sensor concept was applied in a study of absorption and desorption of water in ethylene-vinyl-acetate (EVA) films laminated between two glass sheets. The rate of desorption at a temperature difference of 25°C between the sample and the surroundings was 16 times higher than the rate of absorption at ambient temperature. This result indicates that unframed, EVA-encapsulated modules are likely to dry out in sunny conditions. The degradation of thin-film modules in outdoor operation was the second area of interest in this thesis. A de-encapsulation method for characterizing field degradation in thin-film modules was presented and applied to CdTe modules. It was observed that small-area sampling is especially well suited for characterizing module fill factor degradation. A data filtering methodology was also developed to improve the accuracy of data analysis in field tests. The method was applied to CIGS modules and was found to be especially useful in the analysis of low-irradiance data and current parameters. Additionally, thermal modeling of building integrated a-Si modules was used to predict thermal stress in different European locations. The diagnostics developed in this thesis open up possibilities for improving thin-film module lifetime by enabling precise testing of the moisture-protection properties of encapsulants and by providing methods for identifying degradation mechanisms in field-tested modules.reviewe

Study of the effects of ethylene oxide-freon 12 upon properties of polymers and metallic surfaces Final report, 10 Oct. 1964 - 31 Mar. 1966

Physical, mechanical, and electrical tests to determine the effects on polymeric products after exposure to ethylene oxide-Freon 1

Reliability and Ecological Aspects of Photovoltaic Modules

Photovoltaic (PV) solar energy is expected to be the world's largest source of electricity in the future. To enhance the long-term reliability of PV modules, a thorough understanding of failure mechanisms is of vital importance. In addition, it is important to address the potential downsides to this technology. These include the hazardous chemicals needed for manufacturing solar cells, especially for thin-film technologies, and the large number of PV modules disposed of at the end of their lifecycles. This book discusses the reliability and environmental aspects of PV modules

Review of world experience and properties of materials for encapsulation of terrestrial photovoltaic arrays

Published and unpublished information relating to encapsulation systems and materials properties was collected by searching the literature and appropriate data bases (over 1,300 documents were selected and reviewed) and by personal contacts including site and company visits. A data tabulation summarizing world experience with terrestrial photovoltaic arrays (50 installations) is presented in the report. Based on criteria of properties, processability, availability, and cost, candidate materials were identified which have potential for use in encapsulation systems for arrays with a lifetime of over 20 years high reliability, an efficiency greater than 10 percent, a total price less than $500/kW, and a production capacity of 500,000 kW/yr. The recommended materials (all commercially available) include, depending upon the device design, various borosilicate and soda-lime glasses and numerous polymerics suitable for specific encapsulation system functions

The effect of radiation on electrical insulating materials

Radiation effects on electrical insulating material

Evaluation de couches barrières biocompatibles pour l’encapsulation de dispositifs médicaux microélectroniques

Miniaturized medical devices are becoming increasingly adopted by doctors and patients because they enable new treatment and monitoring capabilities, minimally invasive surgery, improved portability and ease of use. Recent examples include micro pacemakers, micro cochlear implants and ex-situ micro glucose sensors. However, implantable micro devices employing packaging technologies other than metallic enclosures are yet to be seen. Physiological monitors such as in-situ pressure sensors and BioMEMS could profit significantly from advances in thin barrier films for corrosion protection of silicon micro devices. Coating films that stop the diffusion and permeation of harmful substances are necessary to protect both the patient and the micro device. Ceramic films deposited by chemical vapor deposition techniques are good candidates for this task due to their low permeability to gases, low chemical reactivity and high conformality. However, few studies are available about the corrosion protection offered by biocompatible coatings to microelectronic devices in representative biological environments.Ten materials were selected in this thesis after a bibliographic study: Al2O3, BN, DLC, HfO2, SiC, SiN, SiO2, SiOC, TiO2 and ZnO. Ultra-thin films of these materials (5-100 nm) were deposited by plasma enhanced chemical vapor deposition (PECVD) or atomic layer deposition (ALD) on substrates commonly found in electronic micro devices: crystalline silicon, copper, tungsten nitride and polyimide. In vitro cytotoxicity tests and degradation tests were performed for several weeks at different temperatures in Phosphate Buffer Saline (PBS) and NaCl supplemented with 10% Fetal Bovine Serum (NaCl/FBS). Changes in thickness and chemical composition were monitored by VASE, XPS and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). It was found that SiO2 and SiN films (generally used for protection in the microelectronics industry) are not stable in PBS and NaCl/FBS at 37°C, even though they act as good hermetic barriers. Al2O3 showed very good stability in saline solution and excellent behavior as gas barrier, but it was rapidly dissolved in NaCl/FBS.In contrast, films of DLC, SiOC and TiO2 showed very low chemical reactivity in both mediums. Finally, it was shown that multilayers of TiO2 on Al2O3 offer the best performance as hermetic and diffusion barriers for corrosion protection of silicon micro systems in saline environments.Les dispositifs médicaux miniaturisés sont de plus en plus répandus dans le monde médical, car ils offrent de nouvelles opportunités de traitement et de surveillance. La miniaturisation des systèmes permet notamment une chirurgie minimalement invasive, une portabilité améliorée et une facilité d'utilisation. Parmi les exemples on peut mentionner les micro-stimulateurs cardiaques, les micro-implants cochléaires et les micro-capteurs ex-situ de glucose. Cependant, les micro-dispositifs implantables qui utilisent des technologies d'assemblage autres que les boîtiers métalliques sont encore à découvrir. La surveillance de paramètres physiologiques à l'aide de capteurs in-situ de pression et BioMEMS pourraient bénéficier des progrès faits sur les études d'encapsulation en couche mince destinées à protéger les micro-dispositifs de silicium contre la corrosion. En effet, une barrière qui empêche la diffusion et la pénétration des substances nocives est indispensable pour protéger à la fois le patient et le micro-dispositif. Les couches minces céramiques déposées par des procédés chimiques en phase vapeur sont de bons candidats grâce à leurs faibles perméabilités aux gazes, faibles réactivités chimique et conformités de dépôt élevées. Cependant, dans des milieux biologiques représentatifs du corps humain, peu d'études ont été réalisées dans le domaine de la protection des dispositifs microélectroniques contre la corrosion.Au cours de cette thèse, dix matériaux, choisis à l'issue d'une étude bibliographique, ont été étudiés: Al2O3, BN, DLC, HfO2, SiC, SiN, SiO2, SiOC, TiO2 et ZnO. Des couches ultrafines de ces matériaux (de 5 à 100 nm) ont été déposées par voie chimique en phase vapeur assisté par plasma (PECVD) ou par couches atomiques (ALD) sur des substrats silicium recouverts de matériaux généralement présents dans des dispositifs microélectroniques tels que le silicium cristallin, le cuivre, le tungstène nitrure et le poly-imide. Des mesures de cytotoxicité ont été réalisées et des tests de vieillissement ont été effectués pendant plusieurs semaines à des températures différentes dans une solution saline phosphatée (PBS) mais aussi dans une solution à base de sérum de veau fœtale (NaCl/SVF). Les changements dans la composition chimique et l'épaisseur ont été suivies par VASE, XPS et spectroscopie de masse d'ions secondaires à temps de vol (TOF-SIMS). Il a été montré que les couches de SiO2 et de SiN (généralement utilisées pour la protection dans l'industrie de la microélectronique) n'étaient pas stables dans le PBS et le NaCl/SVF à 37°C, même si en revanche elles offraient une bonne barrière aux gazes. L'Al2O3 a lui montré une très bonne tenu en milieu salin et une remarquable herméticité mais en revanche, il s'est corrodé rapidement dans le NaCl/SVF. Les couches de DLC, SiOC et TiO2 ont donné les meilleurs résultats de stabilité dans le PBS et le sérum de veau. Enfin, il a aussi été montré dans cette thèse que l'empilement TiO2 sur Al2O3 offrait la meilleure efficacité comme barrière hermétique et diffusive pour la protection des microsystèmes de silicium contre la corrosion dans les milieux salins

Selection of paste and glue elements for CPV modules

Tese de mestrado em Engenharia da Energia e do Ambiente, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2010This thesis reports on the progress of the development of encapsulation methods and materials to use in the HSUN PV receiver. The HSUN is a concentration photovoltaic (CPV) system concept under development by WS Energia. After a thorough description of the encapsulation state of the art, two main approaches were tested: Ethylene Vinyl Acetate (EVA) laminates and Silicone stacks. Experimental results were unsatisfactory regarding the EVA laminates. The curing process was not fully optimized which lead to (i) the appearance of yellowness after exposing the laminate to concentrated irradiation for a few days; and (ii) the increase of the series resistance of the solar cell during the curing process, probably associated to stretching of the soldered contacts. Numerical thermal modelling of the EVA laminate has also shown the need to introduce active cooling of the PV receiver in order to prevent thermal damage to the cell. The silicone stacks tests were satisfactory regarding the optical, mechanical and electrical properties of the PV receiver. Even after a few days of concentrated irradiation there was no evidence of the development of yellowness or moisture. Thermal modelling showed that further optimization of the HSUN receiver concept is required but suggest that passive cooling approaches are probably sufficient to warrant safe thermal conditions for the solar cell even under concentrated irradiation.O desenvolvimento da presente tese é baseado na pesquisa de materiais e desenvolvimento de métodos de encapsulamento. Tem como principal objectivo, uma aplicação no projecto HSUN, que visa o desenvolvimento de um módulo fotovoltaico de concentração (CPV) na WS Energia. Após uma descrição pormenorizada do estado de arte do encapsulamento, foram testadas duas abordagens: Laminação de amostras com Acetato de Etileno Vinil (EVA) e Silicone. Os resultados experimentais podem ser considerados satisfatórios atendendo à qualidade dos laminados de EVA. O processo de cura não estava completamente optimizado o que poderá ter conduzido a (i) aparecimento de amarelamento após exposição das amostras à luz concentrada durante alguns dias; e (ii) o aumento das resistências de série da célula durante o processo de cura. Este facto poderá ser associado ao alongamento dos contactos soldados. A modelação do modelo térmico para o laminado de EVA também demonstrou a necessidade de introdução de um arrefecimento activo no módulo PV de modo a evitar que a temperatura provoque danos nas células. As amostras de silicone revelaram resultados satisfatórios em relação às propriedades ópticas, mecânicas e eléctricas do módulo PV. Após exposição da amostra à concentração solar durante alguns dias, não foi evidenciando o aparecimento de amarelamento ou humidade. O modelo térmico revelou que é necessária uma optimização do conceito HSUN. As aproximações efectuadas sugerem que um modelo de arrefecimento passivo será suficiente para garantir as condições óptimas para a célula quando submetida à irradiação concentrada

A STUDY ON THE DURABILITY AND PERFORMANCE OF PHOTOVOLTAIC MODULES IN THE TROPICS

Ph.DDOCTOR OF PHILOSOPH