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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 NTRS1980

Solar flux incident on an orbiting surface after reflection from a planet

Algorithms describing the solar radiation impinging on an infinitesimal surface after reflection from a gray and diffuse planet are derived. The following conditions apply: only radiation from the sunny half of the planet is taken into account; the radiation must fall on the top of the orbiting surface, and radiation must come from that part of the planet that can be seen from the orbiting body. A simple approximate formula is presented which displays excellent accuracy for all significant situations, with an error which is always less than 5% of the maximum possible reflected flux. Attention is also given to solar albedo flux on a surface directly facing the planet, the influence of solar position on albedo flux, and to solar albedo flux as a function of the surface-planet tilt angle.

Modest, M. F.↗
NASA NTRS1971

Effects of positive ion implantation into antireflection coating of silicon solar cells

The state of technological development of Si solar cells for highest obtained efficiency and radiation resistance is summarized. The various theoretical analyses of Si solar cells are reviewed. It is shown that factors controlling blue response are carrier diffusion length, surface recombination, impurity concentration profile in surface region, high level of surface impurity concentration (degeneracy), reflection coefficient of oxide, and absorption coefficient of Si. The theory of ion implantation of charge into the oxide antireflection coating is developed and side effects are discussed. The experimental investigations were directed at determining whether the blue response of Si solar cells could be improved by phosphorus ion charges introduced into the oxide antireflection coating.

Middleton, A. E.↗
NASA NTRS1987

Diffusion length measurements in bulk and epitaxially grown 3-5 semiconductors using charge collection microscopy

Diffusion lengths and surface recombination velocities were measured in GaAs diodes and InP finished solar cells. The basic techniques used was charge collection microscopy also known as electron beam induced current (EBIC). The normalized currents and distances from the pn junction were read directly from the calibrated curves obtained while using the line scan mode in an SEM. These values were then equated to integral and infinite series expressions resulting from the solution of the diffusion equation with both extended generation and point generation functions. This expands previous work by examining both thin and thick samples. The surface recombination velocity was either treated as an unknown in a system of two equations, or measured directly using low e(-) beam accelerating voltages. These techniques give accurate results by accounting for the effects of surface recombination and the finite size of the generation volume.

Leon, R. P.↗
NASA NTRS1987

Diffusion length measurement in bulk and epitaxially grown III-V semiconductors using charge collection microscopy

Diffusion lengths and surface recombination velocities were measured in GaAs diodes and InP finished solar cells. The basic technique used was charge collection microscopy, also known as electron beam induced current (EBIC). The normalized currents and distances from the pn junction were read directly from the calibrated curves obtained while using the line-scan mode in an SEM. These values were then equated to integral and infinite series expressions resulting from the solution of the diffusion equation with both extended-generation and point-generation functions. This expands previous work by examining both thin and thick samples. The surface recombination velocity was either treated as an unknown in a system of two equations or measured directly using low e(-) beam accelerating voltages. These techniques give accurate results by accounting for the effects of surface recombination and the finite size of the generation volume.

Leon, R. P.↗
NASA NTRS1982

Design principles for high efficiency small-grain polysilicon solar cells, with supporting experimental studies

Design principles suggested here aim toward high conversion efficiency (greater than 15 percent) in polysilicon cells. The principles seek to decrease the liabilities of both intragranular and grain-boundary-surface defects. The advantages of a phosphorus atom concentration gradient in a thin (less than 50 microns) base of a p(+)/n(x)/n(+) drift-field solar cell, which produces favorable gradients in chemical potential, minority-carrier mobility and diffusivity, and recombination lifetime (via phosphorus gettering) are suggested. The degrading effects of grain boundaries are reduced by these three gradients and by substituting atoms (P, H, F or Li) for vacancies on the grain-boundary surface. From recent experiments comes support for the benefits of P diffusion down grain boundaries and, for quasi-grain-boundary-free and related structures. New analytic solutions for the n(x)-base include the effect of a power-law dependence between P concentration and lifetime. These provide an upper-bound estimate on the open circuit voltage. Finite-difference numerical solutions of the six Shockley equations furnish complete information about all solar-cell parameters and add insight concerning design.

Lindholm, F. A.↗
NASA NTRS1988

Radiation transfer in plant canopies - Scattering of solar radiation and canopy reflectance

The one-dimensional vertical model of radiation transfer in a plant canopy described by Verstraete (1987) is extended to account for the transfer of diffuse radiation. This improved model computes the absorption and scattering of both visible and near-infrared radiation in a multilayer canopy as a function of solar position and leaf orientation distribution. Multiple scattering is allowed, and the spectral reflectance of the vegetation stand is predicted. The results of the model are compared to those of other models and actual observations.

Verstraete, Michel M.↗
NASA NTRS1978

Development of Surfaces Optically Suitable for Flat Solar Panels

Three areas of research in the development of flat solar panels are described. (1) A reflectometer which can separately evaluate the spectral and diffuse reflectivities of surfaces was developed. The reflectometer has a phase locked detection system. (2) A coating composed of strongly bound copper oxide that is formed by an etching process performed on an aluminum alloy with high copper content was also developed. Because of this one step fabrication process, fabrication costs are expected to be small. (3) A literature search was conducted and conclusions on the required optical properties of flat plate solar collectors are presented.

Desmet, D.↗
NASA NTRS1979

Study of the Effects of Impurities on the Properties of Silicon Materials and Performance of Silicon Solar Cell

Numerical solutions were obtained from the exact one dimensional transmission line circuit model to study the following effects on the terrestrial performance of silicon solar cells: interband Auger recombination; surface recombination at the contact interfaces; enhanced metallic impurity solubility; diffusion profiles; and defect-impurity recombination centers. Thermal recombination parameters of titanium impurity in silicon were estimated from recent experimental data. Based on those parameters, computer model calculations showed that titanium concentration must be kept below 6x10 to the 12th power Ti/cu cm in order to achieve 16% AM1 efficiency in a silicon solar cell of 250 micrometers thick and 1.5 ohm-cm resistivity.

Sah, C. T.↗
NASA NTRS1980

A low-cost photovoltaic cell process based on thick film techniques

The low-cost, easily automated processing for solar cell fabrication being developed at Spectrolab for the DOE LSA program is described. These processes include plasma-etching, spray-on diffusion sources and antireflective coating, thick film metallization, aluminum back contacts, laser scribing and ultrasonic soldering. The process sequence has been shown to produce solar cells having 15% conversion efficiency at AM1 which meet the cell fabrication budget required for the DOE 1986 cost goal of $0.70 per peak watt in 1980.

Mardesich, N.↗
NASA NTRS2001

Our Sun IV: The Standard Model and Helioseismology: Consequences of Uncertainties in Input Physics and in Observed Solar Parameters

Helioseismic frequency observations provide an extremely accurate window into the solar interior; frequencies from the Michaelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory (SOHO) spacecraft, enable the adiabatic sound speed and adiabatic index to be inferred with an accuracy of a few parts in 10(exp 4) and the density with an accuracy of a few parts in 10(exp 3). This has become a Serious challenge to theoretical models of the Sun. Therefore, we have undertaken a self-consistent, systematic study of the sources of uncertainties in the standard solar models. We found that the largest effect on the interior structure arises from the observational uncertainties in the photospheric abundances of the elements, which affect the sound speed profile at the level of 3 parts in 10(exp 3). The estimated 4% uncertainty in the OPAL opacities could lead to effects of 1 part in 10(exp 3); the approximately 5%, uncertainty in the basic pp nuclear reaction rate would have a similar effect, as would uncertainties of approximately 15% in the diffusion constants for the gravitational settling of helium. The approximately 50% uncertainties in diffusion constants for the heavier elements would have nearly as large an effect. Different observational methods for determining the solar radius yield results differing by as much as 7 parts in 10(exp 4); we found that this leads to uncertainties of a few parts in 10(exp 3) in the sound speed int the solar convective envelope, but has negligible effect on the interior. Our reference standard solar model yielded a convective envelope position of 0.7135 solar radius, in excellent agreement with the observed value of 0.713 +/- 0.001 solar radius and was significantly affected only by Z/X, the pp rate, and the uncertainties in helium diffusion constants. Our reference model also yielded envelope helium abundance of 0.2424, in good agreement with the approximate range of 0.24 to 0.25 inferred from helioseismic observations; only extreme Z/X values yielded envelope helium abundance outside this range. We found that other current uncertainties, namely, in the solar age and luminosity, in nuclear rates other than the pp reaction, in the low-temperature molecular opacities, and in the low-density equation of state, have no significant effect on the quantities that can be inferred from helioseismic observations. The predicted pre-main-sequence lithium depletion is uncertain by a factor of 2. The predicted neutrino capture rate is uncertain by approximately 30% for the Cl-27 experiment and by approximately 3% for Ga-71 experiments, while the B-8 neutrino flux is uncertain by approximately 30%.

Boothroyd, Arnold I.↗
NASA NTRS1985

Preliminary study: Moisture-polymer interaction. Stuby objectives

The problems associated with mathematically modeling water-module interaction phenomena, including sorption and desorption, diffusion, and permeation are discussed. With reliable analytical models, an extensive materials data base, and solar radiation surface meteorological observations (SOLMET) weather data, predicting module lifetimes in realistic environments can become a practical reality. The status of the present techniques of simulating the various transport mechanisms was reported. The Dent model (a modified Brunauer-Emmet-Teller) approach represented polyvinyl butyral (PVB) sorption data. A 100-layer material model and Fick's diffusion model gave diffusivity values exhibiting adequate agreement with those measured for PVB. Diffusivity of PVB is concentration dependent, decreasing as the water content in PVB increases. The temperature dependence of diffusion in PVB is well modeled by the Arrhenius rate equation. Equilibrium conductivity and leakage current data are well represented by Hearle's model for bulk ionic conductivity. A nodal network analysis using the Systems Improved Numerical Differencing Analyzer (SINDA) Thermal Analyzer gave reasonable correlation with measurable data. It is concluded that realistic lifetime predictions seem to be feasible.

Wen, L. C.↗
NASA NTRS1985

The large scale dynamics of the outer heliosphere and the long-term modulation of galactic cosmic rays

The network of cosmic ray observatories reaching across the heliosphere has given new insight into the process of solar modulation, establishing that the decreases occur principally in the outer heliosphere and are produced by interplanetary flow systems; that the hysteresis effects appear to be produced by changes in the rigidity dependence of the diffusion coefficient and that the predicted effects on the cosmic ray gradients associated with the reversal of the solar magnetic field polarity are not observed.

Mcdonald, F. B.↗
NASA NTRS1971

Research, Development and Fabrication of Lithium Solar Cells

This report continues studies on cells made with low temperature (<400degC) single-cycle, lithium diffusion schedules. Measurements of concentration of lithium at the back surface showed that C(sub S) changes with time consisting of a build-up to a maximum value (above 10(exp 17) cm(exp -3)) with gradual decrease at longer diffusion times. Using the estimated C(sub S) values, theoretical lithium profiles were calculated. The calculated concentration near the PN junction was higher than those measured by the capacitance voltage (C-V) technique. The calculated concentration gradients were one-seventh of those measured by C-V methods. Both the concentration and its gradient were proportional to C(sub S). Estimates of C(sub S) obtained by extrapolating from C-V measured values of concentration and gradient near the PN junction, showed a decrease in C(sub S) for longer diffusion times. This fact supported the trend observed in Shipment C-13, where,, at longer times, the spread in values of V(sub oc), lithium concentration, and gradient became greater. The general conclusion was that the I-V characteristics were well controlled, with good cell output, but for longer diffusion times the lithium concentration gradient could have wider spread. The work described has led to greater insight into the lithium distribution dependence on the surface conditions. The surface conditions could be changed by varying the method used to apply lithium. Vacuum evaporation of lithium shows promise, and another exhaustive test of this method is in progress. Shipment C-13 is summarized, and the succeeding lots (C-14, C-15) are described. It is felt that improved monitoring of cell properties is at hand, and that the control of cell fabrication processes has advanced to where the effects of subtle differences in lithium distribution can now be seen. Evaluation is continuing on the best method to scale up the fabrication steps. A different sequence of fabrication is planned for Shipments C-14 and C-15.

Iles, Peter A.↗
NASA NTRS1981

Electronic properties of deep-level defects in proton irradiated AlGaAs-GaAs solar cells

Deep level transient spectroscopy and capacitance voltage techniques as well as analysis of the forward current voltage (I-V) characteristics and SEM-EIC data were carried out for proton irradiated GaAs solar cells over a wide range of proton energies and proton fluences. Defect and recombination parameters such as defect energy levels and density, carrier capture cross sections and lifetimes as well as diffusion lengths in the undoped n-GaAs LPE layers were determined. Good correlation between these defect parameters and solar cell performance parameters was obtained for GaAs solar cells irradiated by 200 and 290 KeV protons. It was found that 200 to 290 KeV protons will produce the most defects and damages to the GaAs solar cell structure used. The influence of the low temperature (200 to 400 C) periodic thermal annealing on the deep level defects and the performance of the 200 KeV proton irradiated cells is discussed.

Li, S. S.↗
NASA NTRS1994

Photoevaporation of disks around massive stars and application to ultracompact H II regions

Young massive stars produce sufficient Lyman continuum photon luminosity Phi(sub i) to significantly affect the structure and evolution of the accretion disks surrounding them. A nearly static, ionized, isothermal 10(exp 4) K atmosphere forms above the neutral disk for disk radii r less than r(sub g) = 10(exp 15) M(sub 1) cm, where M(sub *) = 10 solar mass M(sub 1) is the stellar mass. For r approximately greater than r(sub g) the diffuse field created by hydrogen recombinations to the ground state in the photoionized gas above the disk produces a steady evaporation at the surface of the disk, and this H II gas flows freely out to the ISM (the 'disk wind'). The detailed structure depends on the mass-loss rate dot-M(sub w) of the fast, approximately greater than 1000 km/sec, stellar wind from the massive star. A critical mass-loss rate dot-M(sub cr) is defined such that the ram pressure of the stellar wind equals the thermal pressure of the H II atmosphere at r(sub g). In the weak stellar wind solution, dot-M(sub w) less than dot-M(sub cr), the diffuse photons from the atmosphere above r(sub g) produce a photoevaporative mass-loss rate from the disk at r approximately greater than r(sub g) of order 1 x 10(exp -5)(Phi(sub 49))(exp 1/2)(M(sub 1))(exp 1/2) solar mass/year, where Phi(sub i) = 10(exp 49) Phi(sub 49)/sec. The resulting slow (10 to 50 km/sec) ionized outflow, which persists for approximately greater than 10(exp 5) year for disk masses M(sub d) approximately 0.3 M(sub *), may explain the observational characteri stics of unresolved, ultracompact H II regions. In the strong stellar wind solution, dot-M(sub w) greater than dot-M(sub cr), the ram pressure of the stellar wind blows down the atmosphere for r less than r(sub g) and allows the stellar photons to penetrate to greater radii and smaller heights. A slow, ionized outflow produced mainly by diffuse photons is again created for r less than r(sub g); however, it is now dominated by the flow at r(sub w)(greater than r(sub g)), the radius at which the stellar wind ram pressure equals the thermal pressure in the evaporating flow. The mass-loss rate from the disk is of order 6 x 10(exp -5)dot-M(sub w-6) v(sub w8)(Phi (sub 49))(exp -1/2) solar mass/year, where dot-M(sub w-6) = M(sub w)/10(exp -6) solar mass/year and v(sub w8) = v(sub w)/1000 km/sec is the stellar wind velocity. The resulting outflow, which also persists for approximately greater than 10(exp 5) year may explain many of the more extended (r approximately greater than 10(exp 16) cm) ultracompact H II regions. Both the weak-wind and the strong-wind models depend entirely on stellar parameters Phi(sub i), M(sub *), dot-M(sub w)) and are independent of disk parameters as long as an extended r much greater than (r(sub g)), neutral disk exists. We compare both weak-wind and strong-wind model results to the observed radio free-free spectra and luminosities of ultracompact H II regions and to the interesting source MWC 349.

Hollenbach, David↗
NASA NTRS1979

Open-circuit voltage improvements in low-resistivity solar cells

Mechanisms limiting the open-circuit voltage in 0.1 ohm-cm solar cells were investigated. It was found that a rather complicated multistep diffusion process could produce cells with significantly improved voltages. The voltage capabilities of various laboratory cells were compared independent of their absorption and collection efficiencies. This was accomplished by comparing the cells on the basis of their saturation currents or, equivalently, comparing their voltage outputs at a constant current-density level. The results show that for both the Lewis diffused emitter cell and the Spire ion-implanted emitter cell the base component of the saturation current is voltage controlling. The evidence for the University of Florida cells, although not very conclusive, suggests emitter control of the voltage in this device. The data suggest further that the critical voltage-limiting parameter for the Lewis cell is the electron mobility in the cell base.

Godlewski, M. P.↗
NASA NTRS1977

Planetary ionospheres

An analogy is drawn between the Eath's ionosphere and the existence of ionospheres around other planets or natural satellites. An ionosphere is defined as a series of layers (D, E, E1, F2) and their characteristics are discussed. Emphasis is on the role of solar wind impacting with the potential ionosphere and the subsequent chemical and diffusion processes that can be observed. Data from the MARINER and PIONEER space programs are cited concerning measured electron density and ionospheric refractivity of extraterrestrial ionospheres, then an attempt is made to model these atmospheres based on Earth ionosphere theory.

Bauer, S. J.↗
NASA NTRS1979

Low cost processes for silicon

The paper describes the multiple process development of low cost processes for manufacture of silicon. A support program includes subtasks for the modeling of reactions and reactors, chemical engineering and solid-state physics studies, and development of impurity concentration measurement procedures. The preliminary economic analyses indicate total product costs ranging from $5.00 to $8.73/kg based on 1000 MT/yr plants. In the studies of impurity effects, a model which considers that degradations of solar cell performance by impurities are primarily due to decreases in base diffusion length was constructed from experimental data.

Lutwack, R.↗