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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Irradiation and measurements of fluorinated ethylene-propylene-A on silicon solar cells in vacuum

Silicon monoxide (SiO) coated silicon solar cells covered with fluorinated ethylene-propylene-A (FEP-A) were irradiated by 1-MeV electrons in vacuum. The effect of irradiation on the light transmittance of FEP-A was checked by measuring the short-circuit current of the cells while in vacuum after each dose increment, immediately after the irradiation, and again after a minimum elapsed time of 16 hr. The results indicated no apparent loss in transmission due to irradiation of FEP-A and no delamination from the SiO surface while the cells were in vacuum, but embrittlement of FEP-A occurred at the accumulated dose.

Marsik, S. J.↗
NASA NTRS1975

Effect of electron irradiation in vacuum on FEP-A silicon solar cell covers

Fluorinated ethylene-propylene-A (FEP-A) covers on silicon solar cells were irradiated with 1-MeV electrons, in vacuum, to an accumulated fluence equivalent to approximately 28 years in synchronous orbit. The effect of irradiation on the light transmittance of FEP-A was checked by measuring the short-circuit current of the cells after each dose increment. The results indicate no apparent overall loss in transmission due to irradiation of FEP-A. Filter wheel measurements revealed some darkening of the FEP-A at the blue end of the spectrum. Although no delamination from the cell surface was observed while in vacuum, embrittlement of FEP-A occurred at the accumulated dose.

Marsik, S. J.↗
NASA NTRS1974

Results of the first 150 days of the NTS-1 solar cell experiments

Twelve solar cell experiments were on the Naval Research Laboratory NTS-1 satellite launched on 14 July 1974, into a 13,260 km circular orbit at an inclination of 125 deg. The experiment comprises: 2 ohm-cm n/p, lithium-diffused p/n, violet n/p, p(+) back surface field, and ultra-thin wrap around contact cells. The short-circuit current of the experiments ranged from 2 to 12 percent higher in space than under solar simulators. During the 5 year life of the satellite, the experiments will be exposed to radiation equivalent to 2 x 10 to the 15th power 1-MeV electron cm/2 and to nearly 5500 thermal cycles.

Statler, R. L.↗
NASA NTRS1975

Hydrogen diffusion and trapping in nickel

An analysis of hydrogen transport in pure polycrystalline nickel foils and rods at 300-550 K shows that both trapping and short-circuit diffusion are present and have small yet significant effects on permeation, evolution, and absorption. Both effects appear to be associated primarily with the dislocation substructure of nickel. Relations describing hydrogen transport in nickel are obtained using the data on deuterium permeation, tritium absorption, and outgassing in pure polycrystalline nickel together with earlier measurements of diffusivity and solubility of hydrogen isotopes.

Louthan, M. R., Jr.↗
NASA NTRS1975

Effect of electron irradiation in vacuum on FEP-A silicon solar cell covers

The effect of irradiation on the light transmittance of ethylene-propylene-A (FEP-A) was investigated by measuring the short-circuit current of the cells after each of several electron dose increments, immediately after total irradiation, and 16 hours after total irradiation. Results indicated no apparent overall loss in transmission due to irradiation of FEP-A. However, filter wheel measurements revealed a 'darkening' of the FEP-A at the blue end of the spectrum. Some embrittlement of the FEP-A occurred at an accumulated dose of 67,500,000 rads.

Marsik, S. J.↗
NASA NTRS1976

High photovoltages in ferroelectric ceramics

The short-circuit currents and photo-emfs were measured for various ceramics including barium titanate, lead metaniobate, and lead titanate. It is suggested that the emfs and currents arise from the presence of photoconductor-insulator sandwiches in the presence of space-charge-produced internal fields. Results are in agreement with the proposed theory and indicate that the ferroelectric ceramics are not only producers of high-voltage photoelectricity but a photo-battery, the polarity and magnitude of which can be switched by application of an electrical signal.

Brody, P. S.↗
NASA NTRS1975

Space calibration of standard solar cells using high altitude sounding rockets

Four photovoltaic cells were space calibrated and successfully recovered from a NASA Aerobee rocket launched on Sept. 18, 1974, which reached a peak altitude of 251 km. The experiment was comprised of four 2 ohm-cm n/p cells, two of which are optically filtered with 0.6 to 0.9 micron bandpass filters. The short-circuit current agreed to within 4% of the laboratory calibration. The variation of cell output due to atmospheric attenuation between the altitude range 80 and 251 km was 0.4% for the unfiltered cells.

Thomas, N. L.↗
NASA NTRS1975

Current status of silicon solar cell technology

Recent advances in solar cell technology have led to the development of laboratory cells with efficiencies above 15% and production cells with efficiencies in the area of 13%. The increased output is largely the result of increases in the short-circuit current. The most significant gain in the amount of light entering the cell has been obtained through surface texturing by chemical etching techniques. Sheet resistances resulting from phosphorus diffusion in the 800 C temperature range yield junction depths on the order of 0.1 micrometer, leading to significant increases in the blue region of the cell spectral response. The inclusion of a back surface field in 10 ohm-cm cells has produced an increase in open-circuit voltage of about 50 mV and an increase in the minority carrier lifetime. It appears that a low emitter efficiency of the diffused region is the cause of poor voltages. Future research will be primarily directed toward correcting this deficiency and toward the development of low cost production methods.

Brandhorst, H. W., Jr.↗
NASA NTRS1975

High altitude calibration of solar cells using rockets

The use of sounding rockets for calibrating solar cells offers two principal advantages: there is no effect due to the terrestrial atmosphere and the cells are recoverable immediately after calibration. Four n/p photovoltaic cells were calibrated in space and successfully recovered from a NASA Aerobee rocket that reached a peak altitude of 251 km. Two of the cells were optically filtered with 0.6 to 0.9-micron bandpass filters. The short-circuit current agreed to within 4% of the laboratory calibration; variation of cell output due to atmospheric attenuation in the altitude range of 80 to 251 km was 0.4% for the unfiltered cells.

Thomas, N. L.↗
NASA NTRS1976

Efficient photovoltaic heterojunctions of indium tin oxides on silicon

Heterojunction diodes of indium tin oxide films sputtered on to p-silicon using ion-beam techniques display significant photovoltaic effects when exposed to sunlight. Galvanomagnetic and optical measurements confirm that the oxide films are highly degenerate transparent semiconductors. At a tin oxide concentration of 10%, an open-circuit voltage of 0.51 V was observed along with a short-circuit current of 32 mA/sq cm, a fill factor of 0.70, and a conversion efficiency of 12%. As the concentration was raised to 70%, the voltage remained steady, the current fell to 27 mA/sq cm, and the fill factor fell to 0.60

Dubow, J. B.↗
NASA NTRS1976

Effect of atmospheric parameters on silicon cell performance

The effects of changing atmospheric parameters on the performance of a typical silicon solar cell were calculated. The precipitable water vapor content, airmass and turbidity were varied over wide ranges and the normal terrestrial distribution of spectral irradiance was studied. The cell short-circuit current was then computed for each spectral irradiance distribution using the cell spectral response. Data are presented in the form of calibration number (cell current/incident irradiance) vs. water vapor content or turbidity.

Curtis, H. B.↗
NASA NTRS1977

Radiation tests of SEP solar cells

Solar cells specially designed for Solar Electric Propulsion (SEP) were tested with radiation fluences up to 10 to the 12th power protons having energies of 1.5, 1.0, and 0.5 MeV, and with fluences up to 10 to the 16th power electrons having 1.0 MeV energy. Spectrolab cells having a back-surface field were also irradiated with the same particles and fluences. Cell performances are described by curves in which normalized and absolute values of maximum power, maximum-power voltage, short-circuit current, and open-circuit voltage are plotted as a function of fluence.

Oman, H.↗
NASA NTRS1978

Endurance testing of first generation (Block 1) commercial solar cell modules

To determine lifetimes of the first generation (Block 1) commercial solar cell modules used in solar cell arrays, a program was initiated to expose these modules to a range of environments. The conditions endured by these modules encompassed hot and dry, hot and humid, tropical rain forests, sea-air, urban industrial and urban clean. Exposures were for periods up to 1 year. The effect of outdoor exposure on the performance of the modules was determined using current-voltage curves. Short-circuit current (I sub sc) and maximum power (P sub max) were the parameters monitored. In all cases, there was a loss of performance of the modules with outdoor exposure.

Anagnostou, E.↗
NASA NTRS1976

Basic corrections to predictions of solar cell performance required by nonlinearities

The superposition principle is used to derive the approximation that the current-voltage characteristic of an illuminated solar cell is the dark current-voltage characteristic shifted by the short-circuit photocurrent. The derivation requires the linearity of the boundary value problems that underlie the electrical characteristics. The shifting approximation is invalid if considerable photocurrent and considerable dark current both occur within the junction space-charge region; it is invalid also if sizable series resistance is present or if high-injection concentrations of holes and electrons exist within the quasi-neutral regions.

Lindholm, F. A.↗
NASA NTRS1978

Analysis of the interaction of an electron beam with a solar cell. I. II

The short-circuit current generated by the electron beam of a scanning electron microscope when it impinges on the N-P junction of a solar cell is known to be dependent on the configuration used to investigate the cell's response, and the situation for one specific configuration is analyzed. This configuration is the case in which the highly collimated electron beam strikes the edge of a planar junction a variable distance away from the edge of the depletion layer. An earlier treatment is generalized to encompass the ohmic contact at the back surface. The analysis employing Fourier and Wiener-Hopf techniques shows that it is impractical to determine the bulk diffusion length of a solar cell by a SEM used in the studied configuration unless the ohmic contact is partially removed.

Von Roos, O.↗
NASA NTRS1978

Lifetime and diffusion length measurements on silicon material and solar cells

Experimental methods were evaluated for the determination of lifetime and diffusion length in silicon intentionally doped with potentially lifetime-degrading impurities found in metallurgical grade silicon, impurities which may be residual in low-cost silicon intended for use in terrestrial flat-plate arrays. Lifetime measurements were made using a steady-state photoconductivity method. Diffusion length determinations were made using short-circuit current measurements under penetrating illumination. Mutual consistency among all experimental methods was verified, but steady-state photoconductivity was found preferable to photoconductivity decay at short lifetimes and in the presence of traps. The effects of a number of impurities on lifetime in bulk material, and on diffusion length in cells fabricated from this material, were determined. Results are compared with those obtained using different techniques. General agreement was found in terms of the hierarchy of impurities which degrade the lifetime.

Othmer, S.↗
NASA NTRS1977

Epitaxial solar-cell fabrication, phase 2

Dichlorosilane (SiH2Cl2) was used as the silicon source material in all of the epitaxial growths. Both n/p/p(+) and p/n/n(+) structures were studied. Correlations were made between the measured profiles and the solar cell parameters, especially cell open-circuit voltage. It was found that in order to obtain consistently high open-circuit voltage, the epitaxial techniques used to grow the surface layer must be altered to obtain very abrupt doping profiles in the vicinity of the junction. With these techniques, it was possible to grow reproducibly both p/n/n(+) and n/p/p(+) solar cell structures having open-circuit voltages in the 610- to 630-mV range, with fill-factors in excess of 0.80 and AM-1 efficiencies of about 13%. Combinations and comparisons of epitaxial and diffused surface layers were also made. Using such surface layers, we found that the blue response of epitaxial cells could be improved, resulting in AM-1 short-circuit current densities of about 30 mA/cm sq. The best cells fabricated in this manner had AM-1 efficiency of 14.1%.

Daiello, R. V.↗
NASA NTRS1977

Optimum antireflection coating for Antireflection-coated Metal-Oxide-Semiconductor /AMOS/ solar cells

Consideration is given to the design of a single-layer optimum antireflection coating for AMOS (antireflection-coated metal-oxide-semiconductor) solar cells to match the entire sunlight spectrum. The energy conversion efficiency is maximized by maximizing the open-circuit voltage and the short-circuit current. The former is maximized by oxidation techniques and the latter is maximized by the light-coupling into the solar cell. With reference to the effective index of refraction as obtained by ellipsometry, examples of optimum antireflection coatings for 60-A Au-GaAs solar cells are presented.

Yeh, Y. C. M.↗