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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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At least 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

I-V-T analysis of radiation damage in high efficiency Si solar cells

A detailed analysis of current-voltage characteristics of N(+)-P/P solar cells indicate that there is a combination of different mechanisms which results in an enhancement in the dark current and in turn deteriorates the photovoltaic performance of the solar cells after 1 MeV e(-) irradiation. The increase in the dark current is due to three effects, i.e., bulk recombination, space charge recombination by deep traps and space charge recombination through shallow traps. It is shown that the increase in bulk recombination current is about 2 to 3 orders of magnitude whereas space charge recombination current due to shallow traps increases only by an order or so and no space charge recombination through deep traps was observed after irradiation. Thus, in order to improve the radiation hardness of these devices, bulk properties should be preserved.

Banerjee, S.↗
NASA NTRS1985

Materials requirements for high-efficiency silicon solar cells

To achieve higher Si solar cell efficiencies (greater than 20%), better single-crystal Si must be produced. It is believed possible to bring Cz (Czochralski) Si up to the same low recombination level as FZ (Float Zone) Si. It is also desirable that solar cell Si meet the following requirements: long minority carrier lifetime (0.2 ohm-cm p-type with tau less than 500 microsec); repeatedly uniform lifetime (not spread from 50 to 1000 microsec); a lifetime that does not decrease during normal device processing; a silicon wafer sheet that is flat and stays throughout normal device processing; uniform and reasonable mechanical strength; and, manufacture at low cost (less than $50/sq m).

Wolf, M.↗
NASA NTRS1985

The status of silicon ribbon growth technology for high-efficiency silicon solar cells

More than a dozen methods have been applied to the growth of silicon ribbons, beginning as early as 1963. The ribbon geometry has been particularly intriguing for photovoltaic applications, because it might provide large area, damage free, nearly continuous substrates without the material loss or cost of ingot wafering. In general, the efficiency of silicon ribbon solar cells has been lower than that of ingot cells. The status of some ribbon growth techniques that have achieved laboratory efficiencies greater than 13.5% are reviewed, i.e., edge-defined, film-fed growth (EFG), edge-supported pulling (ESP), ribbon against a drop (RAD), and dendritic web growth (web).

Ciszek, T. F.↗
NASA NTRS1985

Heavy doping considerations and measurements in high-efficiency cells

Theoretical work on heavily doped silicon was described. Heavily doped polysilicon was used as a back-surface passivant replacing the usual back-surface field (BSF). Very good first results were achieved and there is the promise of a simple, low temperature deposition process. Short-circuit current-decay measurement methods were also covered.

Lindholm, F.↗
NASA NTRS1986

Impurity effects in silicon for high efficiency solar cells

Model analyses indicate that sophisticated solar cell designs including, e.g., back surface fields, optical reflectors, surface passivation, and double layer antireflective coatings can produce devices with conversion efficiencies above 20 percent (AM1). To realize this potential, the quality of the silicon from which the cells are made must be improved; and these excellent electrical properties must be maintained during device processing. As the cell efficiency rises, the sensitivity to trace contaminants also increases. For example, the threshold Ti impurity concentration at which cell performance degrades is more than an order of magnitude lower for an 18-percent cell. Similar behavior occurs for numerous other metal species which introduce deep level traps that stimulate the recombination of photogenerated carriers in silicon. Purification via crystal growth in conjunction with gettering steps to preserve the large diffusion length of the as-grown material can lead to the production of devices with efficiencies aboved 18 percent, as has been verified experimentally.

Hopkins, R. H.↗
NASA NTRS1986

Device research task (processing and high-efficiency solar cells)

This task has been expanded since the last 25th Project Integration Meeting (PIM) to include process research in addition to device research. The objective of this task is to assist the Flat-plate Solar Array (FSA) Project in meeting its near- and long-term goals by identifying and implementing research in the areas of device physics, device structures, measurement techniques, material-device interactions, and cell processing. The research efforts of this task are described and reflect the deversity of device research being conducted. All of the contracts being reported are either completed or near completion and culminate the device research efforts of the FSA Project. Optimazation methods and silicon solar cell numerical models, carrier transport and recombination parameters in heavily doped silicon, development and analysis of silicon solar cells of near 20% efficiency, and SiN sub x passivation of silicon surfaces are discussed.

Source record↗
NASA NTRS1986

Development of high-efficiency solar cells on silicon web

Achievement of higher efficiency cells by directing efforts toward identifying carrier loss mechanisms; design of cell structures; and development of processing techniques are described. Use of techniques such as deep-level transient spectroscopy (DLTS), laser-beam-induced current (LBIC), and transmission electron microscopy (TEM) indicated that dislocations in web material rather than twin planes were primarily responsible for limiting diffusion lengths in the web. Lifetimes and cell efficiencies can be improved from 19 to 120 microns, and 8 to 10.3% (no AR), respectively, by implanting hydrogen at 1500 eV and a beam current density of 2.0 mA/sq cm. Some of the processing improvements included use of a double-layer AR coating (ZnS and MgF2) and an addition of an aluminum back surface reflectors. Cells of more than 16% efficiency were achieved.

Meier, D. L.↗
NASA NTRS1985

Studies of the nature of interfacial barriers in high efficiency crystalline silicon solar cells

The effects of interfacial barriers in crystalline silicon solar cells were studied. The effort was directed toward the investigation and use of such techniques as Angular Resolved Parameter Spectroscopy (ARAPS) and Impedance Spectroscopy in initially characterizing n-type Si doped to levels commonly used for n+p solar cells, and eventually Si solar cells. The objectives of the research are given. Those accomplished are detailed, as are recommendations for future work.

Bates, Clayton W., Jr.↗
NASA NTRS1987

GaAs high efficiency limits/geometric enhancements

This workshop addressed efficiency improvements that may be obtained in GaAs solar cells. The cell designs considered by the group ranged from conventional planar structures to novel devices employing superlattices or point contacts.

Spitzer, Mark↗
NASA NTRS1986

High efficiency crystalline silicon solar cells

The factors which may limit current crystalline silicon solar cells to less than 20 percent efficiency at AM 1 are investigated together with the factors which may limit the ultimate efficiency achievable. It was found that base recombination at residual defect and impurity recombination centers was the likely cause of the 20-percent efficiency barrier. Suggestions for design changes that would cut the losses due to recombinations are presented.

Sah, C. T.↗
NASA NTRS1986

Investigation of high efficiency silicon MINP solar cells

This paper includes results of both theoretical and experimental studies of silicon metal insulator n/p cells. Performance calculations are described which give expected efficiencies as a function of base resistivity. Fabrication and characterization of cells are discussed, and detailed analyses of current loss mechanisms are presented. Using 0.2-ohm cm FZ material and Mg tunneling contacts, AM 1 efficiencies in the range of 16.5-17 percent have been achieved.

Olsen, L. C.↗
NASA NTRS1985

Superstructures and multijunction cells for high efficiency energy conversion

Potential applications of superlattices to photovoltaic structures are discussed. A single-bandgap, multijunction cell with selective electrodes for lateral transport of collected carriers is proposed. The concept is based on similar doping superlattice (NIPI) structures. Computer simulations show that by reducing bulk recombination losses, the spectral response of such cells is enhanced, particularly for poor quality materials with short diffusion lengths. Dark current contributions of additional junctions result in a trade-off between short-circuit current and open-circuit voltage as the number of layers is increased. One or two extra junctions appear to be optimal.

Wagner, M.↗
NASA NTRS1985

High-efficiency double-heterostructure AlGaAs/GaAs solar cells

Double-heterostructure solar cells have been fabricated from wafers prepared by using organometallic chemical vapor deposition to grow a p GaAs absorbing layer sandwiched between p(+) and n(+) AlGaAs layers. The best cell, which incorporates an abrupt AlGaAs/GaAs shallow heterojunction, exhibits a global AM1 one-sun conversion efficiency of 23 percent. The rate at which the open-circuit voltage decreases with increasing temperature is lower for the double-heterostructure cells than for GaAs shallow-homojunction cells.

Gale, R. P.↗
NASA NTRS1985

Simulation analysis of a novel high efficiency silicon solar cell

It is recognized that crystalline silicon photovoltaic module efficiency of 15 percent or more is required for cost-effective photovoltaic energy utilization. This level of module efficiency requires large-area encapsulated production cell efficiencies in the range of 18 to 20 percent. Though the theoretical maximum of silicon solar cell efficiency for an idealized case is estimated to be around 30 percent, practical performance of cells to-date are considerably below this limit. This is understood to be largely a consequence of minority carrier losses in the bulk as well as at all surfaces including those under the metal contacts. In this paper a novel device design with special features to reduce bulk and surface recombination losses is evaluated using numerical analysis technique. Details of the numerical model, cell design, and analysis results are presented.

Mokashi, Anant R.↗
NASA NTRS1987

High efficiency photon counting detectors for the FAUST Spacelab far ultraviolet astronomy payload

The performances of sealed tube microchannel-plate position sensitive detectors having transmission CsI photocathodes or opaque CsI photocathodes are compared. These devices were developed for the FAUST Spacelab payload to accomplish imaging surveys in the band between 1300 A and 1800 A. It is demonstrated that photocathode quantum efficiencies in excess of 40 percent at 1216 A have been achieved with the transmission and the opaque CsI photocathodes. The effect of the photoelectron trajectory on the spatial resolution is assessed. Spatial resolution of less than 70 microns FWHM has been obtained and is maintained up to event rates of 50,000/sec. Background rates of 0.55 events sq cm per sec have been achieved and low distortion (less than 1 percent) imaging has been demonstrated.

Siegmund, O. H. W.↗
NASA NTRS1988

High efficiency, long life traveling wave tubes for future communications satellites

Electron beam devices, primarily traveling wave tubes (TWTs), have been used as the power amplifiers in almost all space communications and data transmission systems. Based on the technology that is presently available and the expected success of current research efforts, it is reasonable to predict the development of a new class of microwave TWTs with efficiencies in excess of 60 percent and lifetimes of at least 10 years. Because of this rapid advance of technology, the TWT is expected to remain the dominant device for power amplifiers in space.

Dayton, James A., Jr.↗
NASA NTRS1986

Development in tunable solid state lasers with high spectral purity, high efficiency and long lifetime for differential absorption lidar

The paper presents a review of tunable vibronic solid state lasers for DIAL measurements and provides new experimental results for tunable Ti:sapphire lasers, materials development, and spectral bandwidth narrowing through injection control. Pulsed injection control of a Ti:sapphire laser with a 2.5-pm narrow band pulsed dye laser and with another Ti:sapphire laser is demonstrated with nearly complete energy extraction, indicating homogeneous line broadening. The status of tunable solid state lasers in the 1.6-2.3 micron range for DIAL measurements of trace gases, and development trends for lasers with reduced cryogenic cooling needs, are included. The effects of laser gain on optical damage, energy extraction, and amplified spontaneous emission are indicated for several tunable lasers.

Hess, R. V.↗