Electricity from photovoltaic solar cells: Flat-Plate Solar Array Project final Report. Volume III: Silicon sheet: wafers and ribbons

The Flat-Plate Solar Array (FSA) Project, funded by the U.S. Government and managed by the Jet Propulsion Laboratory, was formed in 1975 to develop the module/array technology needed to attain widespread terrestrial use of photovoltaics by 1985. To accomplish this, the FSA Project established and managed an Industry, University, and Federal Government Team to perform the needed research and development. The primary objective of the Silicon Sheet Task of the FSA Project was the development of one or more low-cost technologies for producing silicon sheet suitable for processing into cost-eompetitive solar cells. Silicon sheet refers to high-purity crystalline silicon of size and thickness for fabrication into solar cells. The Task effort began with state-of-the-art sheet technologies and then solicited and supported any new silicon sheet alternatives that had the potential to achieve the Project goals. A total of 48 contracts were awarded that covered work in the areas of ingot growth and casting, wafering, ribbon growth, other sheet technologies, and programs of supportive research. Periodic reviews of each sheet technology were held, assessing the technical progress and the long-range potential. Technologies that failed to achieve their promise, or seemed to have lower probabilities for success in comparison with others, were dropped. A series of workshops was initiated to assess the state of the art, to provide insights into problems remaining to be addressed, and to support technology transfer. The Task made and fostered significant improvements in silicon sheet including processing of both ingot and ribbon technologies. An additional important outcome was the vastly improved understanding of the characteristics associated with high-quality sheet, and the control of the parameters required for higher efficiency solar cells. Although significant sheet cost reductions were made, the technology advancements required to meet the Task cost goals were not achieved. This FSA Final Report (JPL Publication 86-31, 5101-289, DOE/JPL 1012-125, October 1986) is composed of eight volumes, consisting of an Executive Summary and seven technology reports: Volume I: Executive Summary. Volume II: Silicon Material. Volume III: Silicon Sheet: Wafers and Ribbons Volume IV: High-Efficiency Solar Celis. Volume V: Process Development. Volume VI: Engineering Sciences and Reliability. Volume VII: Module Encapsulation. Volume VIII: Project Analysis and Integration. Two supplemental reports included in the final report package are: FSA Project: 10 Years of Progress, JPL Document 400-279. 5101-279, October 1985. Summary of FSA Project Documentation: Abstracts of Published Documents, 1975 to 1986, JPL Publication 82-79 (Revision 1),5101-221, DOE/JPL-1 012-76, September 1986

Macrosegregation in direct-chill casting of aluminium alloys

This is the post-print version of the final paper published in Progress in Materials Science. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2008 Elsevier B.V.Semi-continuous direct-chill (DC) casting holds a prominent position in commercial aluminium alloy processing, especially in production of large sized ingots. Macrosegregation, which is the non-uniform chemical composition over the length scale of a casting, is one of the major defects that occur during this process. The fact that macrosegregation is essentially unaffected by subsequent heat treatment (hence constitutes an irreversible defect) leaves us with little choice but to control it during the casting stage. Despite over a century of research in the phenomenon of macrosegregation in castings and good understanding of underlying mechanisms, the contributions of these mechanisms in the overall macrosegregation picture; and interplay between these mechanisms and the structure formation during solidification are still unclear. This review attempts to fill this gap based on the published data and own results. The following features make this review unique: results of computer simulations are used in order to separate the effects of different macrosegregation mechanisms. The issue of grain refining is specifically discussed in relation to macrosegregation. This report is structured as follows. Macrosegregation as a phenomenon is defined in the Introduction. In “Direct-chill casting – process parameters, solidification and structure patterns” section, direct-chill casting, the role of process parameters and the evolution of structural features in the as-cast billets are described. In “Macrosegregation in direct-chill casting of aluminium alloys” section, macrosegregation mechanisms are elucidated in a historical perspective and the correlation with DC casting process parameters and structural features are made. The issue of how to control macrosegregation in direct-chill casting is also dealt with in the same section. In “Role of grain refining” section, the effect of grain refining on macrosegregation is introduced, the current understanding is described and the contentious issues are outlined. The review is finished with conclusion remarks and outline for the future research.The Netherlands Institute for Metals Researc

Ultrasonic Cavitation Treatment of Metallic Alloys

This Special Issue scrutinizes the use of ultrasonic-cavitation melt treatment in technology of high-quality metallic alloys with improved mechanical properties, and assesses the driving mechanisms of cavitation-induced effects, such as grain refinement, degassing, wetting, and particle distribution. In this context, the research published in this Special Issue considers the interaction between the cavitation field and acoustic streaming with the melt flow and the suspended solid/liquid phases, the characterization and mapping of cavitation activity in a melt volume, and the possibility of achieving high efficiency in processing large melt volumes through technological approaches for the commercial implementation of ultrasonic processing technology

The 19th Project Integration Meeting

The Flat-Plate Solar Array Project is described. Project analysis and integration is discussed. Technology research in silicon material, large-area silicon sheet and environmental isolation; cell and module formation; engineering sciences, and module performance and failure analysis. It includes a report on, and copies of visual presentations made at, the 19th Project Integration Meeting held at Pasadena, California, on November 11, 1981

Clean & Green: Best Practices in Photovoltaics

Outlines the impact of using toxic compounds in manufacturing solar panels compared to the effects of fossil fuels and nuclear power; best management and operations practices for protecting workers and the environment; and considerations for investors

THERMAL POST-FABRICATION PROCESSING OF Y2O3:Tm CERAMIC SCINTILLATORS

The effects of thermal post-fabrication processing in O2 flux on the luminescence and scintillation of Y2O3:Tm transparent ceramics were investigated. The material\u27s microstructure, optical properties, and scintillation properties were characterized using X-ray diffraction, attenuated total reflectance Fourier transform infrared spectroscopy, thermoluminescence measurements, differential pulse height distribution measurements, Archimedes density measurements, photoluminescence measurements, and ultra violet-visible transmission measurements. The processing is effective if performed in the time frame of 60-120mins at 1050°C under oxygen flow. After the first hour of processing, about 40% enhancement in the luminescence output together with about 20% enhancement in the scintillation light yield were observed. The enhancements were tentatively assigned to the incorporation of oxygen into vacancy sites. Longer cumulative processing times lead to the incorporation of oxygen as interstitials that is detrimental to scintillation light yield but not to luminescence output. This work also revealed that thermoluminescence measurements are a useful tool to predict scintillation light yield of Y2O3:Tm

Electricity from photovoltaic solar cells. Flat-Plate Solar Array Project of the US Department of Energy's National Photovoltaics Program: 10 years of progress

The objectives were to develop the flat-plate photovoltaic (PV) array technologies required for large-scale terrestrial use late in the 1980s and in the 1990s; advance crystalline silicon PV technologies; develop the technologies required to convert thin-film PV research results into viable module and array technology; and to stimulate transfer of knowledge of advanced PV materials, solar cells, modules, and arrays to the PV community. Progress reached on attaining these goals, along with future recommendations are discussed

Index to 1984 NASA Tech Briefs, volume 9, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1984 Tech B Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Multi-scale defect engineering and interface modifications for enhancement of thermoelectric properties in nanostructured bulk materials

Among various static energy conversion technologies, the thermoelectric (TE) energy conversion has gained the considerable interest due to its reliability and ability to directly convert waste heat into electricity. In TE conversion technology, physical properties such as thermopower (α), electrical (σ) and thermal conductivity (κ) are exploited simultaneously to convert waste heat into electricity. The efficiency of such conversion depends upon various factors such as temperature, figure of merit (ZT= α2σ/ κ) etc. An inherent coupling among α, σ and κ limits ZT and thereby constrains one in achieving high efficiency. Many efforts have been carried out in decoupling TE properties. The inherent coupling of TE properties resulted in a saturation of the field for several years. Recently, it is realized that the inclusion of multi-length scale defects plays an important role in tuning the TE properties of various materials. Defects are often perceived as imperfections in materials that could adversely affect their performance. On the contrary, because of the limited size scale of nanomaterials, the power of defects could be effectively utilized to selectively scatter phonons and filter low-energy carriers. Hence, it is important to control the length scale and nature of these defects to improve the desired TE properties. This dissertation is focused on answering this important question: `Can one achieve control over the nature and length scale of these defects to decouple and and tune the temperature dependence of ZT in nanostructured bulk materials?\u27 To answer this question, three different materials systems were studied in this work demonstrating the role of various length scales and nature of defects. Firstly, the effects of extrinsic point defects, such as rattlers (Ce, In, Ba, Yb), dopants (Co, Ni) and secondary phases on FeSb3 and CoSb3 based p-type skutterudites on the transport and magnetic properties is studied. `Phonon glass and electron crystal\u27 like behavior was observed in Ni-doped skutterudites. Interestingly, we found that the addition of In facilitated the formation of secondary phases with various morphologies upon surpassing the filling fraction limits. Such in-situ secondary phases were in fact found to be beneficial to the system altering their electrical transport properties, and thereby increasing the ZT of the system as compared to that of the parent compound. The highest ZT value of 0.9 at 650 K was reported for p-type skutterudite sample with nominal composition In0.1Ce0.9Fe3.5Ni0.5Sb12. In the low temperature regime (T \u3c 150K), the electrical transport and magnetic susceptibility exhibited single-ion Kondo-like behavior. The crystal field effects due to the splitting of ground state of Ce (4f level) in presence of cubic crystalline field were observed to dictate the magnetic properties below 100 K. Further, our magnetic susceptibility data is consistent with a crystal field splitting gap of ~39 meV (~450 K). The intrinsic surface or interfacial defects in elemental Bismuth were introduced by controlling the surface-to-volume ratio using a combination of high energy ball-milling and spark plasma sintering (SPS) processes. The obtained ball-milled powders were SPS processed with different ON-OFF time ratios of the DC current pulses to further modify the nature and extent of these surfaces. The `double decoupling\u27 (simultaneous optimization of the thermopower, electrical conductivity and thermal conductivity) in single element polycrystalline Bi was observed via a combination of an increase in the surface-to-volume ratio achieved by ball milling process and an interface (or grain boundary) modification by the SPS process. As a result, a greater than six-fold improvement in the PF, and hence ZT, was achieved in polycrystalline bulk Bi samples. Our detailed studies of the effect of SPS conditions on the transport properties of polycrystalline Bi strongly suggests that surface states play a prominent role in enhancing the TE performance of Bi. Lastly, planar or two-dimensional defects were introduced by chemical exfoliation of layered chalcogenide n-type Bi2Te3. Particularly, chemical exfoliation allows for the introduction of micro-structured scattering centers at multiple length scales while preserving the basal plane properties needed for high ZT values. Mechanical process such as, grinding, sintering and exfoliation are known to generate donor- like defects. In this method, the possible introduction of positively charged defects (TeBi antisites/Te vacancies) on the grain boundaries resulted in: i) the injection of electrons into the bulk increasing carrier concentration, and ii) a potential barrier that selectively filtered low-energy minority carriers (holes in case of n-type Bi2Te3 samples) and thereby, shifting the bipolar (two carrier contribution) effects to higher temperatures. This effect is clearly reflected in the thermopower and thermal conductivity data. Thus, the shift in the bipolar effects results in the shift of ZT maxima to higher temperature, where peak ZT is broadened over a wide temperature range of ~ 150 K. In addition to this, the compatibility factor of our samples exhibits smaller changes over the broad operating temperature regime, making it a good candidate for potential device design