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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 1,153 records · Page 64
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Efficiency enhancement in Si solar cell using 1D quasi-periodic antireflection coating

In order to enhance the efficiency of thin-film Si solar cell, two well-known Fibonacci and Thue–Morse sequences of 1D quasi-periodic structures have been considered to achieve a broadband (300–1100 nm) planar antireflection coating, in this article. As almost non-absorbing materials in the solar spectrum, TiO{sub 2} and SiO{sub 2} with optimized thicknesses are considered to eliminate the reflections in the front side of the solar cell. An optimized bilayer antireflection coating with thicknesses of 54.4 nm and 85.6 nm respectively for the TiO{sub 2} and SiO{sub 2} layers has been obtained. Considering material dispersion and solar power spectrum (AM1.5), maximum efficiency enhancements of 42.78%, 46.15%, and 50% have been achieved for the 3 µm thin-film Si solar cell using the FC(3,1) structure which correspond to the cells without any recombination, with bulk recombination, and with bulk and surface recombinations, respectively. The proposed quasi-periodic multilayer antireflection structures have been investigated and optimized using the TMM and FDTD methods. The electrical characteristic of the design is studied by the drift–diffusion method after extracting the electron–hole pair generation. Also, the stability of the performance of the proposed ARC against induced roughness in practice has been investigated and discussed.

14 SOLAR ENERGY↗
DOE OSTI2019

Tungsten oxide nanostructures and nanocomposites for photoelectrochemical water splitting

Hydrogen production from photoelectrochemical (PEC) water splitting using semiconductor photocatalysts has attracted great attention to realize clean and renewable energy from solar energy. The visible light response of WO 3 with a long hole diffusion length (~150 nm) and good electron mobility (~12 cm 2 V –1 s –1 ) makes it suitable as the photoanode. Yet, WO 3 suffers from issues including rapid recombination of photoexcited electron–hole pairs, photo-corrosion during the photocatalytic process due to the formation of peroxo-species, sluggish kinetics of photogenerated holes, and slow charge transfer at the semiconductor/electrolyte interface. Our report highlights the approaches to overcome these drawbacks of WO 3 photoanodes, including: (i) the manipulation of nanostructured WO 3 photoanodes to decrease the nanoparticle size to promote hole migration to the WO 3 /electrolyte interface which benefits the charge separation; (ii) doping or introducing oxygen vacancies to improve electrical conductivity; exposing high energy crystal surfaces to promote the consumption of photogenerated holes on the high-active crystal face, thereby suppressing the recombination of photogenerated electrons and holes; (iii) decorating with co-catalysts to reduce the overpotential which inhibits the formation of peroxo-species; (iv) other methods such as coupling with narrow band semiconductors to accelerate the charge separation and controlling the crystal phase via annealing to reduce defects. These methods are reviewed with detailed examples.

08 HYDROGEN↗
NASA NTRS1979

The mean free path of low rigidity cosmic rays

A simple heuristic argument is presented which suggests that the large rigidity independent mean free paths observed for low rigidity solar and galactic cosmic rays can be understood in terms of weak turbulence diffusion theory if one assumes that the interplanetary magnetic turbulence consists of a combination of Alfven waves propagating with constant field magnitude and a small (approximately 5-10%) admixture of compressive fluctuations.

Goldstein, M. L.↗
NASA NTRS1978

Induced junction solar cell and method of fabrication

An induced junction solar cell is fabricated on a p-type silicon substrate by first diffusing a grid of criss-crossed current collecting n+ stripes and thermally growing a thin SiO2 film, and then, using silicon-rich chemical vapor deposition (CVD), producing a layer of SiO2 having inherent defects, such as silicon interstices, which function as deep traps for spontaneous positive charges. Ion implantation increases the stable positive charge distribution for a greater inversion layer in the p-type silicon near the surface. After etching through the oxide to parallel collecting stripes, a pattern of metal is produced consisting of a set of contact stripes over the exposed collecting stripes and a diamond shaped pattern which functions as a current collection bus. Then the reverse side is metallized.

Maserjian, J.↗
NASA NTRS1980

The mean free path of low-rigidity cosmic rays

The paper presents a simple heuristic argument that suggests that the large rigidity independent mean free paths observed for low-rigidity solar and galactic cosmic rays can be understood in terms of weak turbulence diffusion theory. This is shown to be possible if it is assumed that the interplanetary magnetic turbulence consists of a combination of Alfven waves propagating with constant field magnitude and a small (about 5-10 percent) admixture of compressive fluctuations.

Goldstein, M. L.↗
NASA NTRS1984

Heavy doping effects in high efficiency silicon solar cells

Several of the key parameters describing the heavily doped regions of silicon solar cells are examined. The experimentally determined energy gap narrowing and minority carrier diffusivity and mobility are key factors in the investigation.

Lindholm, F. A.↗
NASA NTRS1986

Release of noble gases and nitrogen from grain-surface sites in lunar ilmenite by closed-system oxidation

Noble gases and nitrogen were extracted from a 100 to 150 microns ilmenite separate from lunar soil 71501 by closed system stepped heating in approx. 10 torr O2 at 300 C, 400 C, 500 C, 600 C and 630 C, followed by stepped pyrolysis at ten temperatures between 680 C and approx. 1500 C. The five oxidation steps together liberated approx. 65% of the total He-4, 45% of the Ne-20, 23% of the N-14 and Ar-36, 12% of the Kr-84 and 8% of the Xe-132 in the sample; Ne-20/Ar-36 and Ne-20/Ne-22 ratios agree with the solar wind composition experiment, and Kr-84/Ar-36 and Xe-132/Ar-36 are within approx. 10% of Cameron's estimates for the sun and solar wind. The remaining gases, released above 630 C by pyrolysis, are strongly fractionated with respect to the SWC-Cameron solar wind elemental composition. Large concentrations of fractionated noble gases in grain interiors, their virtual absence in the relatively unfractionated surface gas reservoir, and the high N/noble gas ratio all imply that most of the solar wind noble gases initially implanted in grain surfaces are eventually lost by diffusion. Loss limits can be estimated by considering two given scenarios. It is concluded tat approx. 70 to 97% or more of the Ar implanted in 71501 ilmenite grains has diffusively escaped.

Frick, U.↗
NASA NTRS1987

Shallow n(+) diffusion into InP by an open-tube diffusion technique

Very shallow n(+) layers have been obtained in InP by using gallium sulfide as a source for sulfur diffusion, and chemically vapor-deposited SiO2 as a cap. Diffusions were carried out from 585 to 725 C in an open-tube system with a nitrogen ambient. The doping profile of sulfur in InP is estimated to be of the complementary error function type with a surface concentration of 5.6 x 10 to the 18th/cc and a diffusion constant of 1.1 x 10 to the -14th sq cm/s at 670 C. Diodes made on n(+)-p junctions obtained by this diffusion technique show ideality factors close to unity and saturation current densities as low as 3.4 x 10 to the -15th A/sq cm, signifying the presence of a defect-free junction. These diffusions, with junction depths in the 400-700 A range, are ideal for solar cell applications.

Ghandhi, Sorab K.↗
NASA NTRS1988

The budget of biologically active ultraviolet radiation in the earth-atmosphere system

This study applies the concept of a budget to describe the interaction of solar ultraviolet (UV) radiation with the earth-atmosphere system. The wavelength ranges of interest are the biologically relevant UV-B between 280 and 320 nm and the UV-A from 32000 to 400 nm. The Nimbus 7 solar backscattered ultraviolet (SBUV) instrument provides measurements of total column ozone and information concerning cloud cover which, in combination with a simple model of radiation transfer, define the fractions of incident solar irradiance absorbed in the atmosphere, reflected to space, and absorbed at the ground. Results for the month of July quantify the contribution of fractional cloud cover and cloud optical thickness to the radiation budget's three components. Scattering within a thick cloud layer makes the downward radiation field at the cloud base more isotropic than is the case for clear skies. For small solar zenith angles, typical of summer midday conditions, the effective pathlength of this diffuse irradiance through tropospheric ozone is greater than that under clear-sky conditions. The result is an enhanced absorption of UV-B radiation in the troposphere during cloud-covered conditions. Major changes in global cloud cover or cloud optical thicknesses could alter the ultraviolet radiation received by the biosphere by an amount comparable to that predicted for long-term trends in ozone.

Frederick, John E.↗
NASA NTRS1988

Solar-cycle modulation of galactic cosmic rays

This paper describes a numerical solution of the spherically-symmetric, time-dependent, cosmic-ray modulation equation, compares it to data taken near the ecliptic, and probes the physical mechanisms responsible for the solar-cycle variations in the cosmic-ray intensity. With a physically defensible diffusion coefficient and other reasonable parameters, the spectra of protons and electrons can be simulated simultaneously over the cycle, the radial intensity gradients for particles greater than about 100 MeV, the overall intensity variation during the cycle, and the time lag in the recovery of low-energy particles behind high-energy ones, known commonly as the 'hysteresis.' The results suggest that cosmic-ray variations near the ecliptic are dominated by turbulent scattering regions in the heliosphere, overwhelming any effects of gradient and curvature drifts.

Perko, John S.↗
NASA NTRS1989

From interstellar dust to comets

The bulk and microstructure of comet nuclei are derived from the morphological structure and chemical composition of submicron sized interstellar dust grains which have undergone cold aggregation in the pre-solar nebula. The evolutionary picture of dust which is emerging is a cyclic one in which the particles, before being destroyed or going into solar system bodies, find themselves during their 5 billion year lifetime alternately in diffuse clouds and in molecular clouds. A small silicate core captured within a molecular cloud accretes various ices and gradually builds up an inner mantle of organic refractory material which has been produced by photoprocessing of the volatile ices. Clumps of grains form, and then clumps of clumps, and so on, until finally we reach the size of the comet nucleus.

Greenberg, J. M.↗
NASA NTRS1989

Seed population for about 1 MeV per nucleon heavy ions accelerated by interplanetary shocks

Data obtained between 1977 and 1982 by the ISEE 1 and ISEE 3 satellites on the composition of heavy ions of about 1 MeV per nucleon, accelerated in interplanetary shock events which followed solar flare events, are examined. It was found that the average relative abundances for C, O, and Fe in the shock events were very close to those found for energetic ions in the solar flares, suggesting that, at these energies, the shock accelerated particles have the solar energetic particles as their seed population. This hypothesis is supported by the fact that the Fe/O ratio in the solar particle events is very strongly correlated with the Fe/O ratio in associated diffusive shock events.

Tan, L. C.↗
NASA NTRS1991

The substorm current wedge and field-aligned currents in MHD simulations of magnetotail reconnection

Results are reported from a three-dimensional MHD simulation of magnetotail reconnection, which, in contrast to earlier ones, starts from an equilibrium configuration that contains a region 1 type field-aligned current system at the plasma sheet/lobe boundary. This current system is found from equilibrium theory as the consequence of boundary conditions, which require that field lines at large distances from the earth become aligned-with the tail axis, consistent with observations and the expected consequences of the interaction with the solar wind. As in earlier simulations, the dynamic evolution develops from a slow diffusion to the fast growth of a three-dimensional tearing mode, initiated by the sudden occurrence or increase of resistivity, leading again to the formation and subsequent tailward ejection of a plasmoid, associated with fast plasma flows. In addition there are changes of the electric current system which are consistent with the substorm current wedge picture inferred from observations.

Birn, J.↗
NASA NTRS1991

A new solar cycle model including meridional circulation

A kinematic model is presented for the solar cycle which includes not only the transport of magnetic flux by supergranular diffusion and a poleward bulk flow at the sun's surface, but also the effects of turbulent diffusion and an equatorward 'return flow' beneath the surface. As in the earlier models of Babcock and Leighton, the rotational shearing of a subsurface poloidal field generates toroidal flux that erupts at the surface in the form of bipolar magnetic regions. However, such eruptions do not result in any net loss of toroidal flux from the sun (as assumed by Babcock and Leighton); instead, the large-scale toroidal field is destroyed both by 'unwinding' as the local poloidal field reverses its polarity, and by diffusion as the toroidal flux is transported equatorward by the subsurface flow and merged with its opposite hemisphere counterpart. The inclusion of meridional circulation allows stable oscillations of the magnetic field, accompanied by the equatorward progression of flux eruptions, to be achieved even in the absence of a radial gradient in the angular velocity. An illustrative case in which a subsurface flow speed of order 1 m/s and subsurface diffusion rate of order 10 sq km/s yield 22-yr oscillations in qualitative agreement with observations.

Wang, Y.-M.↗