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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Suitability of plastic-encapsulated solid-state electronic devices for use in spacecraft discussed. Conclusion of preliminary study was plasticencapsulated parts sufficiently reliable to be considered for use in lowcost equipment used at moderate temperature and low humidity. Useful to engineers as guides to testing or use of plastic encapsulated semiconductors in severe terrestrial environments.
The evaluation of potentially useful low cost encapsulation materials is discussed. The goal is to identify, evaluate, test and recommend encapsulant materials and processes for the production of cost effective, long life solar cell modules. Technical investigations concerned the development of advanced cure chemistries for lamination type pottants; the continued evaluation of soil resistant surface treatment, and the results of an accelerated aging test program for the comparison of material stabilities. New compounds were evaluated for efficiency in curing both ethylene/vinyl acetate and ethylene/methyl acrylate pottants intended for vacuum bag lamination of solar cells. Two component aliphatic urethane casting syrups were evaluated for suitability as solar module pottants on the basis of optical, physical and fabrication characteristics.
Analytical models were developed to perform optical, thermal, electrical and structural analyses on candidate encapsulation systems. From these analyses several candidate encapsulation systems were selected for qualification testing.
The design and processing techniques necessary to incorporate bypass diodes within the module encapsulant are presented. The Semicon PN junction diode cells were selected. Diode junction to heat spreader thermal resistance measurements, performed on a variety of mounted diode chip types and sizes, have yielded values which are consistently below 1 deg C per watt, but show some instability when thermally cycled over the temperature range from -40 to 150 deg C. Three representative experimental modules, each incorporating integral bypass diode/heat spreader assemblies of various sizes, were designed. Thermal testing of these modules enabled the formulation of a recommended heat spreader plate sizing relationship. The production cost of three encapsulated bypass diode/heat spreader assemblies were compared with similarly rated externally mounted packaged diodes. It is concluded that, when proper designed and installed, these bypass diode devices will improve the overall reliability of a terrestrial array over a 20 year design lifetime.
The availability of high-quality, large-diameter GaAs substrates is key to the successful development and production of high-speed GaAs devices and high-efficiency GaAs solar cells. The liquid encapsulated Czochralski (LEC) technique has provided a means for producing large-diameter GaAs. Progress in improving the LEC growth process which has resulted in 3-inch GaAs crystals with exceptionally low dislocation densities and reduced propensity for twinning is reported. Undoped, semi-insulating GaAs ingots were grown in a Melbourn high-pressure LEC system. The effects of seed perfection, seed necking, cone angle, melt stoichiometry, ambient pressure, thickness of the B2O3 encapsulating layer, and diameter control on the dislocation density were investigated. The material was characterized by preferential etching and X-ray topography. It is shown that 3-inch diameter substrates can be produced with dislocation densities as low as 6000 per sq cm through proper selection and control of growth parameters. Also, the incidence of twinning can be reduced significantly by growing from slightly As-rich melts.
The long term effects of encapsulation individual sheets of the Codex Hammer were investigated. The manuscript was simulated with similar sheets of paper which were photographed under repeatable raking light conditions to enhance their surface texture, encapsulated in plexiglas, cycled in an environmental test chamber, and rephotographed at selected intervals. The film images were digitized, contrast enhanced, geometrically registered, and apodized. An FFT analysis of a control sheet and two experimental sheets indicates no micro-burnishing, but reveals that the ""mesoscale'' deformations with sizes 8mm are degrading monotonically, which is of no concern. Difference image analysis indicates that the sheets were increasingly stressed with time and that the plexiglas did not provide a sufficient environmental barrier under the simulation conditions. The relationship of these results to the Codex itself is to be determined.
Low cost encapsulation materials for the Flat Plate Solar Array Program (FSA) are investigated. The goal of the program is to identify, test, evaluate and recommend encapsulation materials and processes for the fabrication of cost effective and long life solar modules. Accelerated aging techniques for module component lifetime studies, investigation of candidate outer cover films and continued evaluation of soil repellant coatings are also included.
Tests for chemical structure, material properties, water absorption, aging and curing agent of Ethylene Vinyl Acetate (EVA) and UV absorption studies are carried out. A computer model was developed for thermal optical modeling, to investigate dependence between module operating temperature and solar insolation, and heat dissapation behavior. Structural analyses were performed in order to determine the stress distribution under wind and heat conditions. Curves are shown for thermal loading conditions. An electrical isolation was carried out to investigate electrical stress aging of non-metallic encapsulation materials and limiting material flaws, and to develop a computer model of electrical fields and stresses in encapsulation materials. In addition, a mathematical model was developed and tests were conducted to predict hygroscopic and thermal expansion and contraction on a plastic coated wooden substrate. Thermal cycle and humidity freezing cycle tests, partial discharge tests, and hail impact tests were also carried out. Finally, the effects of soiling on the surface of photovoltaic modules were investigated. Two antisoiling coatings, a fluorinated silane and perflourodecanoic acid were considered.
The analytical methodology for advanced encapsulation designs for the development of photovoltaic modules is presented. Analytical models are developed to test optical, thermal, electrical and structural properties of the various encapsulation systems. Model data is compared to relevant test data to improve model accuracy and develop general principles for the design of photovoltaic modules.
The goal of the program is to identify, test, evaluate and recommend encapsulation materials and processes for the fabrication of cost-effective and long life solar modules. Of the $18 (1948 $) per square meter allocated for the encapsulation components approximately 50% of the cost ($9/sq m) may be taken by the load bearing component. Due to the proportionally high cost of this element, lower costing materials were investigated. Wood based products were found to be the lowest costing structural materials for module construction, however, they require protection from rainwater and humidity in order to acquire dimensional stability. The cost of a wood product based substrate must, therefore, include raw material costs plus the cost of additional processing to impart hygroscopic inertness. This protection is provided by a two step, or split process in which a flexible laminate containing the cell string is prepared, first in a vacuum process and then adhesively attached with a back cover film to the hardboard in a subsequent step.
Encapsulation materials for solar cells were investigated. The different phases consisted of: (1) identification and development of low cost module encapsulation materials; (2) materials reliability examination; and (3) process sensitivity and process development. It is found that outdoor photothermal aging devices (OPT) are the best accelerated aging methods, simulate worst case field conditions, evaluate formulation and module performance and have a possibility for life assessment. Outdoor metallic copper exposure should be avoided, self priming formulations have good storage stability, stabilizers enhance performance, and soil resistance treatment is still effective.
Suitably chosen liquid encapsulant placed around melt zone in float-zone crystal-growth system performs four important functions enhancing purity and reducing strains and dislocations in final crystal. In new technique, grow dislocation-free crystals with precisely controlled composition even from materials not amenable to conventional float-zone crystal-growth method. Support provided by encapsulant make it practical to process materials of low surface tension.
The identification and development techniques for low-cost module encapsulation materials were reviewed. Test results were displayed for a variety of materials. The improved prospects for modeling encapsulation systems for life prediction were reported.
Liposomes have been suggested as possible models of precellular systems formed in the early Archean earth from lipids of nonenzymatic origin. Since it is generally accepted that RNA molecules preceded double-stranded DNA molecules as genetic material, the encapsulation of polyribonucleotides within liposomes (made from dipalmitoyl phosphatidylcholine and from egg yolk phosphatidylcholine) was studied. Quantitative determinations show that approximately 50 percent of the available lipids form liposomes, and that up to 5 percent of the polyribonucleotides can be entrapped by them. Also studied was the encapsulation of polyribonucleotides in the presence of urea and cyanamide and of Zn(2+) and Pb(2+).
Results are reported of studying the interaction of moisture with photovoltaic (PV) modules and custom-built test coupons in both laboratory and outdoor ambient environments. Characteristics measured included module cell-to-frame leakage currents, encapsulant bulk and surface currents, glass surface currents, and encapsulant/glass interface currents as functions of temperature and humidity. Using a computer model of interelectrode conduction, preferential conduction paths in PVB- and EVA-encapsulated modules are identified. In comparing the results of field and laboratory test environments on identical samples, comments are made about the greater severity of the outdoor environment. Several aspects of water-module interaction, including design strategies and continuing research, are discussed.
Paper reports studies of effects of moisture on photovoltaic modules, presenting data useful in further quantitative studies of such phenomena. Measured data used in computer simulation of two-dimensional conduction to analyze ionic-conduction characteristics of PVB- and EVA-encapsulated modules. Notes encapsulant plays important role in electrochemical processes in photovoltaic module. Indicates how variations in design parameters affect levels of leakage currents in modules. Points out likely leakage-current paths in modules at various temperatures and humidities. Compares results of field and laboratory tests of same specimens and notes greater severity of outdoor environment.
The composition and the annealing characteristics of plasma-deposited silicon-nitride encapsulating films on the ion-implanted InP substrates were investigated, using two different substrate-cleaning procedures (organic solvents and HF or HIO3 solutions) prior to encapsulation. The effect of plasma deposition of silicon nitride on the InP substrates was assessed through the current-voltage characteristics of Schottky diodes. Results of XPS analyses showed that the cleaning procedure that employed HF solution left less oxygen on the InP surface than the procedure involving HIO3. No chemical interaction between the film and the substrate was observed before or after annealing.
Eight urethane compounds were evaluated as possible replacement for the existing encapsulating compoounds for electrical cables for the Launch Support System at Kennedy Space Center (KSC). The existing encapsulating compound, PR-1535, contains the curative MOCA 4-4'-Methylene-BIS (2-chloroaniline), which is a suspect carcinogen and hence may be the subject of further restrictions of its use by the Occupational Safety and Health Administration (OSHA). The samples made in the configuration of cable joints and in the form of disks were evaluated for flammability and hypergolic compatibility. These also underwent accelerated weatherability tests that measured the residual hardness of the exposed samples. Three candidates and the existing compound passed the hardness test. Of these, only one candidate and the existing compound passed the flammability test. The thermal and hydrolytic stability (weatherability) of these samples was studied using thermogravimetric analysis (DSC) techniques. The TMA and DSC data correlated with the residual hardness data; whereas, the TGA data showed no correlation. A hypergolic compatibility test will be conducted on the compound V-356-HE80, which passed both the flammability and accelerated weatherability tests.