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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Toward Mass-Production of Transition Metal Dichalcogenide Solar Cells: Scalable Growth of Photovoltaic-Grade Multilayer WSe2 by Tungsten Selenization

Semiconducting transition metal dichalcogenides (TMDs) are promising for high-specific-power photovoltaics due to their desirable band gaps, high absorption coefficients, and ideally dangling-bond-free surfaces. Despite their potential, the majority of TMD solar cells to date are fabricated in a nonscalable fashion, with exfoliated materials, due to the lack of high-quality, large-area, multilayer TMDs. Here, we present the scalable, thickness-tunable synthesis of multilayer WSe2 films by selenizing prepatterned tungsten with either solid-source selenium at 900 degrees C or H2Se precursors at 650 degrees C. Both methods yield photovoltaic-grade, wafer-scale WSe2 films with a layered van der Waals structure and superior characteristics, including charge carrier lifetimes up to 144 ns, over 14x higher than those of any other large-area TMD films previously demonstrated. Simulations show that such carrier lifetimes correspond to ~22% power conversion efficiency and ~64 W g-1 specific power in a packaged solar cell, or ~3 W g-1 in a fully packaged solar module. The results of this study could facilitate the mass production of high-efficiency multilayer WSe2 solar cells at low cost.

carrier lifetime↗
DOE OSTI2020

Insights into Na + Diffusion in Silicon Modules under Operating Conditions: Measuring Low Concentrations by D-SIMS

Sodium induced shunting under an electric field is a challenging reliability issue in crystalline Si solar modules. The source of this Potential-Induced Degradation of the Shunting type (PID-s) is well understood and its influence on power loss has been intensively studied based on phenomenological models on cell or module level relating the experimental power-loss to stressing parameters (time, temperature, voltage). However, little is known about the Na ion migration kinetics, responsible for PID on a microscopic level, and its quantitative relation to the efficiency degradation. In this paper we present our investigations of sodium ion migration in Ethylene-Vinyl Acetate (EVA) and silicon through Dynamic Secondary Ion Mass Spectroscopy (D-SIMS). Each sample was annealed at field relevant temperatures from 60-90 °C to address typical migration mechanisms of common PV installations. Analysis of the SIMS migration profiles revealed a diffusivity constant D 0,EVA = 0.09 ± 0.14 cm 2 /s and an activation energy E A,EVA = 0.85 ± .04 eV for Na in EVA and diffusivities higher than extrapolated literature values in silicon (D 0,Si = (3.03 ± 2.42)x10 -5 cm 2 /s, and E A,Si = 0.98 ± 0.02 eV). The new insight will be included in a drift-diffusion based degradation model accounting for the partition coefficient across all relevant interfaces. This model can assist in predicting PID-failure in the field based on the given model stack and the diffusion of Na + through each material. Furthermore, this tool can be used for process optimization as well as material selection significantly reducing the cost and time to validate a technology.

14 SOLAR ENERGY↗
NASA NTRS1975

Origin and composition of heavy nuclei between 10 and 60 MeV per nucleon during interplanetary quiet times in 1968-1972

Results are reported for measurements of the relative abundances of nuclei from boron through iron in the energy range between 10 and 60 MeV/nucleon which were made with an instrument on board OGO 5 during the period of changing solar modulation from 1968 to 1971. The investigation was conducted to determine whether the heavy nuclei in this energy range were of solar or galactic origin. It is found that the relative abundances are in good agreement with the nuclear abundances of galactic cosmic rays, that the differential energy spectra of carbon and oxygen at these energies diverged from the characteristic modulated galactic spectrum, that changes in the C + N + O flux during this period underwent a temporal phase lag with respect to high-energy galactic cosmic rays, and that this phase lag was the same as that for helium nuclei of galactic origin with energies of 30 to 100 MeV/nucleon. It is concluded that the experimental evidence favors a galactic origin for the present nuclei. Some implications of the energy-spectrum results for cosmic-ray modulation theory are discussed.

Mogro-Campero, A.↗
DOE OSTI2024

Photo-accelerated oxidation of spiro-OMeTAD for efficient carbon-based perovskite solar cells

Metal halide perovskite thin film solar cell (PSC) technology demonstrates promising power conversion efficiency and paves the way to commercialization. So far, the best device performance originates from the n-i-p structure with FTO/SnO 2 /perovskite/Spiro-OMeTAD/Au device architecture. Traditionally, to achieve high efficiency, several hours of oxidization of a Li-doped Spiro-OMeTAD hole transport layer (HTL) is necessary, which hinders the application of Spiro-OMeTAD for rapid large-scale manufacturing. In particular, the oxidization process significantly relies on ambient conditions, including oxygen and moisture levels. In this work, we report a fast technique to accomplish rapid oxidation in several mins of Spiro-OMeTAD HTL in perovskite solar cells by illuminating in visible light with one Sunlight intensity (100 mW cm −2 ). Compared to the traditional approach, our photo-accelerated oxidization of Spiro-OMeTAD approach can deliver a high-power conversion efficiency. We employ this photo-accelerated oxidization for the planar carbon-based perovskite solar cell and achieve a champion device efficiency of 17.47%. This strategy overcomes the barriers for a simple and rapid means toward mass manufacturing and industrial applications by utilizing Spiro-OMeTAD as the HTL for the perovskite solar module.

14 SOLAR ENERGY↗
NASA NTRS1973

Lunar surface cosmic ray experiment S-152, Apollo 16

This investigation was directed at determining the energy spectra and abundances of low energy heavy cosmic rays (0.03 E or = 150 MeV/nucleon). The cosmic rays were detected using plastic and glass particle track detectors. Particles emitted during the 17 April 1972 solar flare dominated the spectra for energies below about 70 MeV/nucleon. Two conclusions emerge from the low energy data: (1) The differential energy spectra for solar particles vary rapidly for energies as low as 0.05 MeV/nucleon for iron-group nuclei. (2) The abundance ratio of heavy elements changes with energy at low energies; heavy elements are enhanced relative to higher elements increasingly as the energy decreases. Galactic particle fluxes recorded within the spacecraft are in agreement with those predicted taking into account solar modulation and spacecraft shielding. The composition of the nuclei at energies above 70 MeV/nucleon imply that these particles originate outside the solar system and hence are galactic cosmic rays.

Fleischer, R. L.↗
NASA NTRS1973

Radial gradients of galactic cosmic ray protons and helium nuclei

Variation of the cosmic ray intensity as a function away from the sun and its radial derivative is studied by plotting satellite cosmic ray measurements against sea level neutron monitor data. Results show that the solar modulation cavity extends well beyond 2 AU and that irregularities in the sun's magnetic field are carried outward radially by the solar wind, thus sweeping low energy cosmic rays out of the solar system and at the same time cooling cosmic rays reaching the earth.

Teegarden, B. J.↗
NASA NTRS1980

High resolution measurements of galactic cosmic-ray neon, magnesium, and silicon isotopes

High-resolution measurements of the abundances of individual isotopes of neon, magnesium and silicon in galactic cosmic rays are reported. The Caltech Heavy Isotope Spectrometer Telescope on board the ISEE 3 spacecraft was used to obtain measurements in the range 30 to 180 MeV/n at an rms mass resolution of 0.20 amu. Results indicate excesses of Ne-22 as well as Mg-25 and Mg-26 in galactic cosmic rays with respect to their solar system abundances. Calculations of the effects of interstellar propagation and solar modulation on cosmic-ray isotope abundances also imply an Mg-25 + Mg-26 cosmic ray source fraction significantly greater than the solar system fraction, and it is suggested that the cosmic ray source material and solar system material were synthesized under different conditions.

Mewaldt, R. A.↗
NASA NTRS1995

The middle atmospheric response to short and long term solar UV variations: analysis of observations and 2D model results

We have investigated the middle atmospheric response to the 27-day and 11-yr solar UV flux variations at low to middle latitudes using a two-dimensional photochemical model. The model reproduced most features of the observed 27-day sensitivity and phase lag of the profile ozone response in the upper stratosphere and lower mesosphere, with a maximum sensitivity of +0.51% per 1% change in 205 nm flux. The model also reproduced the observed transition to a negative phase lag above 2 mb, reflecting the increasing importance with height of the solar modulated HO(x) chemistry on the ozone response above 45 km. The model revealed the general anti-correlation of ozone and solar UV at 65-75 km, and simulated strong UV responses of water vapor and HO(x) species in the mesosphere. Consistent with previous 1D model studies, the observed upper mesospheric positive ozone response averaged over +/- 40 was simulated only when the model water vapor concentrations above 75 km were significantly reduced relative to current observations. In agreement with observations, the model computed a low to middle latitude total ozone phase lag of +3 days and a sensitivity of +0.077% per 1% change in 205 nm flux for the 27-day solar variation, and a total ozone sensitivity of +0.27% for the 11-yr solar cycle. This factor of 3 sensitivity difference is indicative of the photochemical time constant for ozone in the lower stratosphere which is comparable to the 27-day solar rotation period but is much shorter than the 11-yr solar cycle.

Fleming, Eric L.↗
NASA NTRS2006

The Projection of Space Radiation Environments with a Solar Cycle Statistical Model

A solar cycle statistical model has been developed to project sunspot numbers which represent the variations in the space radiation environment. The resultant projection of sunspot numbers in near future were coupled to space-related quantities of interest in radiation protection, such as the galactic cosmic radiation (GCR) deceleration potential (f) and the mean occurrence frequency of solar particle event (SPE). Future GCR fluxes have been derived from a predictive model, in which GCR temporal dependence represented by f was derived from GCR flux and ground-based Climax neutron monitor rate measurements over the last four decades. Results showed that the point dose equivalent inside a typical spacecraft in interplanetary radiation fields was influenced by solar modulation up to a factor of three. One important characteristic of sporadic SPEs is their mean frequency of occurrence, which is dependent on solar activity. Projections of future mean frequency of SPE occurrence were estimated from a power law function of sunspot number. Furthermore, the cumulative probabilities of SPE during short-period missions were defined with the continuous database of proton fluences of SPE. The analytic representation of energy spectra of SPE was constructed by the Weibull distribution for different event sizes. The representative exposure level at each event size was estimated for the guideline of protection systems for astronauts during future space exploration missions.

Kim, Myung-Hee↗
NASA NTRS1986

Modulation of galactic cosmic rays in the heliosphere

Observations of the intensity of galactic cosmic rays and anomalous components near earth and in the outer heliosphere are providing important tests for theories of solar modulation. The most recent observations show effects that seem to require that models for modulation include gradient and curvature drifts as well as the conventional processes of convection, adiabatic deceleration, and diffusion. New observations are required to define the interplay of these processes in the three-dimensional heliosphere.

Mckibben, R. B.↗
NASA NTRS1985

Solar cycle variations of the anomalous cosmic ray component

The intensity of the anomalous cosmic ray component, consisting of He, N, O, and Ne, has long been known to be especially sensitive to the effects of solar modulation. Following its discovery in 1972, this component dominated the quiet time flux of cosmic ray nuclei below approx. 30 MeV/nucleon during the 1972 to 1978 solar minimum, but then became essentially unobservable at 1 AU with the approach of solar maximum conditions. One recent theoretical model predicts substantial differences in the intensity of the anomalous fluxes from one solar minimum period to the next because of the reversal of the solar magnetic field. Using data from the Caltech experiments on IMP-8 and ICE (ISEE-3), the intensity of anomalous O and He at 1 AU during the years 1972 to 1985 is reported in particular. Whether the anomalous fluxes will return to their 1972-1978 levels, as predicted by spherically symmetric modulation models, or whether they will fail to return to 1 AU, as suggested by modulation models in which gradient and curvature drifts dominate are to be determined. The preliminary analysis of data from 1984 shows that the intensity of 8 to 27 MeV/nucleon O is still more than an order of magnitude below its 1972 to 1978 levels, while the intensity of 25 to 43 MeV/nucleon He is a factor of Approx. 8 below its maximum level in 1977.

Mewaldt, R. A.↗
NASA NTRS1980

Solar cells and modules from dentritic web silicon

Some of the noteworthy features of the processes developed in the fabrication of solar cell modules are the handling of long lengths of web, the use of cost effective dip coating of photoresist and antireflection coatings, selective electroplating of the grid pattern and ultrasonic bonding of the cell interconnect. Data on the cells is obtained by means of dark I-V analysis and deep level transient spectroscopy. A histogram of over 100 dentritic web solar cells fabricated in a number of runs using different web crystals shows an average efficiency of over 13%, with some efficiencies running above 15%. Lower cell efficiency is generally associated with low minority carrier time due to recombination centers sometimes present in the bulk silicon. A cost analysis of the process sequence using a 25 MW production line indicates a selling price of $0.75/peak watt in 1986. It is concluded that the efficiency of dentritic web cells approaches that of float zone silicon cells, reduced somewhat by the lower bulk lifetime of the former.

Campbell, R. B.↗
NASA NTRS1985

Solar cycle variations of the anomalous cosmic ray component

The intensity of the anomalous cosmic ray component, consisting of He, N, O, and Ne, has long been known to be especially sensitive to the effects of solar modulation. Following its discovery in 1972, this component dominated the quiet-time flux of cosmic ray nuclei below approximately 30 MeV/nucleon during the 1972 to 1978 solar minimum, but then became essentially unobservable at 1 AU with the approach of solar maximum conditions. One recent theoretical model predicts substantial differences in the intensity of the anomalous fluxes from one solar minimum period to the next because of the reversal of the solar magnetic field. Using data from the Caltech experiments on IMP-8 and ICE (ISEE-3), the intensity of anomalous O and He at 1 AU during the years 1972 to 1985 is reported. We hope to determine whether the anomalous fluxes will return to their 1972 to 1978 levels, as predicted by spherically symmetric modulation models, or whether they will fail to return to 1 AU, as suggested by modulation models in which gradient and curvature drifts dominate.

Mewaldt, R. A.↗
NASA NTRS1989

Solar dynamic power module design

Studies have shown that the use of solar dynamic (SD) power for the growth areas of the Space Station Freedom program will result in life cycle cost savings when compared to power supplied by photovoltaic sources. In the SD power module, a concentrator collects and focuses solar energy into a heat receiver which has integral thermal energy storage. A Power Conversion Unit (PCU) based on the closed Brayton cycle removes thermal energy from the receiver and converts that energy to electrical energy. Since the closed Brayton cycle is a single phase gas cycle, the conversion hardware (heat exchangers, turbine, compressor, etc.) can be designed for operation in low earth orbit, and tested with confidence in test facilities on earth before launch into space. The concentrator subassemblies will be aligned and the receiver/PCU/radiator combination completely assembled and charged with gas and cooling liquid on earth before launch to, and assembly on, orbit.

Secunde, Richard R.↗
DOE OSTI2020

Effects of Photovoltaic Module Materials and Design on Module Deformation Under Load

Static structural finite element models of an aluminum-framed crystalline silicon (c-Si) photovoltaic (PV) module and a glass-glass thin film PV module were constructed and validated against experimental measurements of deflection under uniform pressure loading. Parametric analyses using Latin Hypercube Sampling (LHS) were performed to propagate simulation input uncertainties related to module material properties, dimensions, and manufacturing tolerances into expected uncertainties in simulated deflection predictions. This exercise verifies the applicability and validity of finite element modeling for predicting mechanical behavior of solar modules across architectures and enables computational models to be used with greater confidence in assessment of module mechanical stressors and design for reliability. Sensitivity analyses were also performed on the uncertainty quantification data sets using linear correlation coefficients to elucidate the key parameters influencing module deformation. This information has implications on which materials or parameters may be optimized to best increase module stiffness and reliability, whether the key optimization parameters change with module architecture or loading magnitudes, and whether parameters such as frame design and racking must be replicated in reduced-scale reliability studies to adequately capture full module mechanical behavior.

14 SOLAR ENERGY↗
NASA NTRS1991

Studies of low-energy Galactic cosmic-ray composition at 22 AU. I - Secondary/primary ratios

Data from the High Energy Telescope of the CRS experiment on Voyager 2 have been used to measure the intensity, spectra, and elemental abundances of Galactic cosmic rays from Be to Ni at about 100 MeV/n. The charge resolution of this telescope varies from sigma = 0.034 for oxygen to sigma = 0.11 for iron. The solar modulation deceleration parameter Phi relevant for these data is estimated to be around 300 MV (Phi = 150 MeV/n for particles with A/Z = 2), an unprecedently low level for such measurements. This low modulation parameter is a result of the measurements being made in the outer heliosphere at a heliocentric distance of 22 AU, and centered on the solar minimum period of cycle 21. The results on secondary/primary ratios are used to test the Leaky-Box model of cosmic ray propagation, using the most recent cross sections data in hydrogen and helium, and taking into account the effects of the ionized fraction of the interstellar medium. It is found that all the secondary/primary ratios up to P/S are completely consistent with an exponential pathlength distribution (PLD). This PLD shape also accounts for the Sc-V/Fe ratio.

Ferrando, P.↗