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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 19 records

Predicted performance of InP solar cells in Cassegrainian and slats space concentrator arrays at 20 to 100 AM0, 80 to 100 C

Researchers have calculated the expected performance dependence of near-optimally designed shallow homojunction n+pp+InP solar cells on incident intensities up 200 AM0 and temperatures up to 100 C (373K). Both circular and rectangular cells have been considered, the former for use in a Cassegrainian concentrator array at 100 AM0, 80 to 100 C and the latter for use in a Slats type concentrator array at 20 AM0 80 to 100 C. Calculation of the temperature dependence of the performance parameters I sub sc, V sub oc, FF and eta was done by first verifying that the use of the measured temperature variation of I sub sc, of the best published value of the temperature dependence of the bandgap of InP, and of the temperature dependences of the lifetimes and mobilities of electrons and holes the same as in equivalently doped GaAs, gave calculated results that closely matched measured data on the temperature variation of I sub sc, V sub oc, and FF of four existing InP cells at 1 AM0. It was then assumed that the same temperature dependences of I sub sc, the bandgap and lifetimes and mobilities would hold in the near-optimally designed cells at the higher concentrations.

Goradia, Chandra↗

The Extrapolation of High Altitude Solar Cell I(V) Characteristics to AM0

The high altitude aircraft method has been used at NASA GRC since the early 1960's to calibrate solar cell short circuit current, ISC, to Air Mass Zero (AMO). This method extrapolates ISC to AM0 via the Langley plot method, a logarithmic extrapolation to 0 air mass, and includes corrections for the varying Earth-Sun distance to 1.0 AU and compensating for the non-uniform ozone distribution in the atmosphere. However, other characteristics of the solar cell I(V) curve do not extrapolate in the same way. Another approach is needed to extrapolate VOC and the maximum power point (PMAX) to AM0 illumination. As part of the high altitude aircraft method, VOC and PMAX can be obtained as ISC changes during the flight. These values can then the extrapolated, sometimes interpolated, to the ISC(AM0) value. This approach should be valid as long as the shape of the solar spectra in the stratosphere does not change too much from AMO. As a feasibility check, the results are compared to AMO I(V) curves obtained using the NASA GRC X25 based multi-source simulator. This paper investigates the approach on both multi-junction solar cells and sub-cells.

Snyder, David B.↗

Results from the first international AM0

AM0 solar cell calibration laboratories throughout the world are working together to create standard methods for AM0 calibration. In an effort to compare the results of different calibration methods, five different laboratories calibrated GaAs and Si solar cells. The results of this inter-comparison are presented herein.

round robin solar cells AM0 silicon GaAs internati↗

Calculation Method for Predicting AM0 Isc from High Altitude Aircraft Flight Data

High altitude aircraft have been used by the space photovoltaic (PV) community to determine the air mass Zero (AM0) performance of solar cells for over fifty years. Relative to in-space measurement opportunities, these methods are generally cheaper and more readily available. The data obtained, however, must be corrected for residual atmospheric effects. This paper details the correction method currently being used for the calculation of the estimated AM0 short-circuit current (Isc) for photovoltaic devices flown on the NASA ER-2 calibration platform. This method would also be applicable to other high altitude methods where Isc data is collected over a sufficiently large range of altitudes. An initial comparison with a four junction (4J) cell flown on the CASOLBA high altitude balloon platform showed an agreement to 0.2%.

AM0↗

AM0 efficiency measurements

Procedures for measuring the air mass zero (AM0) current versus voltage characteristics and calculating the efficiency are discussed. The various factors influencing the determination of the efficiency include the I-V measurement system, reference cell calibration, standard reporting conditions, area measurement, light source characteristics, temperature measurement and control, and the measurement procedures. Each of these sources contributes to the precision index and bias limit which is combined to obtain the total uncertainty in the efficiency. These factors are discussed as well as how to minimize differences in the reported AM0 efficiency of a given PV cell between various laboratories.

Emery, Keith↗

A Summary of The 2000-2001 NASA Glenn Lear Jet AM0 Solar Cell Calibration Program

Calibration of solar cells for space is extremely important for satellite power system design. Accurate prediction of solar cell performance is critical to solar array sizing, often required to be within 1%. The NASA Glenn Research Center solar cell calibration airplane facility has been in operation since 1963 with 531 flights to date. The calibration includes real data to Air Mass (AM) 0.2 and uses the Langley plot method plus an ozone correction factor to extrapolate to AM0. Comparison of the AM0 calibration data indicates that there is good correlation with Balloon and Shuttle flown solar cells. This paper will present a history of the airplane calibration procedure, flying considerations, and a brief summary of the previous flying season with some measurement results. This past flying season had a record 35 flights. It will also discuss efforts to more clearly define the ozone correction factor.

Scheiman, David↗

Calculation Method for Predicting AM0 Isc from High Altitude Aircraft Flight Data

High altitude aircraft have been used by by the space photovoltaic (PV) community to determine the Air Mass Zero (AM0) performance of solar cells for over fifty years. Relative to in-space measurement opportunities, these methods are generally cheaper and more readily available. The data obtained, however, must be corrected for residual atmospheric effects. This paper details the correction method currently being used for the calculation of the AM0 short-circuit current (Isc) for photovoltaic devices flown on the NASA ER-2 (Earth Resources-2) calibration platform. This method would also be applicable to any other high altitude method where Isc data is collected over a sufficiently large range of altitudes.

Myers, Matthew G.↗

A 25.5 percent AM0 gallium arsenide grating solar cell

Recent calculations have shown that significant open circuit voltage gains are possible with a dot grating junction geometry. The feasibility of applying the dot geometry to the GaAs cell was investigated. This geometry is shown to result in voltage approach 1.120 V and efficiencies well over 25 percent (AM0) if good collection efficiency can be maintained. The latter is shown to be possible if one chooses the proper base resistivity and cell thickness. The above advances in efficiency are shown to be possible in the P-base cell with only minor improvements in existing technology.

Weizer, V. G.↗

An empirical study of the performance of APMOVPE AM0 InP homojunction solar cells as a function of emitter thickness and doping, and base doping

Their excellent radiation resistance and conversion efficiencies greater than 20 percent, measured under global conditions, make InP shallow-homojunction solar cells very attractive for space or terrestrial application. In addition, modeling studies show that, for optimized design, efficiencies of these devices should exceed 20 percent even under AM0 conditions. However, a systematic experimental investigation of the influence of the various cell design parameters on cell performance has not as yet been made. For the n+/p/p+ structures investigated in the previous modeling study, the design parameters include the impurity concentrations and thicknesses of the emitter and base layers. In the work reported here, researchers discuss an experimental investigation of the effects on cell performance of varying the impurity concentrations of the emitter and base and thickness of the emitter.

Wanlass, M. W.↗

High altitude AM0 testing of PV concentrator lens elements

Recently, the NASA Lewis Research Center modified its Lear High Altitude Test Facility to fly two prototype ENTECH minidome Fresnel lens photovoltaic concentrator elements. The tests were highly successful, and the results verified the ability of the Lear High Altitude Facility to measure the optical performance of individual concentrator lens elements and concentrator/cell combinations at near AM0 insolation conditions. The two concentrator lenses flown achieved optical efficiencies, based on a gallium arsenide concentrator cell response, of 89.8 percent and 90.0 percent. The flights demonstrated the ability of the aircraft to maintain the pointing accuracy required to obtain useful data. With proper alignment of the collimating tube and the pilot's sunsight, this facility could easily maintain a pointing accuracy of + or - 0.5 deg for a sufficiently long time to obtain accurate, reproducible results.

Piszczor, M. F.↗

Lightweight concentrator module with 30 percent AM0 efficient GaAs/GaSb tandem cells

A concept is presented for an aerospace concentrator module with lightweight domed lenses and 30 percent AM0 efficient GaAs/GaSb tandem solar cell circuits. The performance of transparent GaAs cells is reviewed. NASA's high-altitude jet flight calibration data for recent GaSb cells assembled with bulk GaAs filters are reported, along with subsequent Boeing and NASA measurements of GaSb I-V performance at various light levels and temperatures. The expected performance of a basic two-terminal tandem concentrator circuit with three-to-one voltage matching is discussed. All of the necessary components being developed to assemble complete flight test coupons are shown. Straightforward interconnect and assembly techniques yield voltage matched circuits with near-optimum performance over a wide temperature range.

Avery, J. E.↗

Ozone Correction for AM0 Calibrated Solar Cells for the Aircraft Method

The aircraft solar cell calibration method has provided cells calibrated to space conditions for 37 years. However, it is susceptible to systematic errors due to ozone concentration in the stratosphere. The present correction procedure applies a 1% increase to the measured Isc values. High band-gap cells are more sensitive to ozone adsorbed wavelengths so it has become important to reassess the correction technique. This paper evaluates the ozone correction to be 1+{O3}sup Fo, where Fo is 29.5x10(exp-6)/d.u. for a Silicon solar cell and 42.2xl0(exp -6)/d.u. for a GaAs cell. Results will be presented for high band-gap cells. A comparison with flight data indicates that this method of correcting for the ozone density improves the uncertainty of AM0 Isc to 0.5%.

Snyder, David B.↗

Investigation of the Carbon Arc Source as an AM0 Solar Simulator for Use in Characterizing Multi-Junction Solar Cells

The operation of multi-junction solar cells used for production of space power is critically dependent on the spectral irradiance of the illuminating light source. Unlike single-junction cells where the spectral irradiance of the simulator and computational techniques may be used to optimized cell designs, optimization of multi-junction solar cell designs requires a solar simulator with a spectral irradiance that closely matches AM0.

Xu, Jianzeng↗

Ozone Correction for AM0 Calibrated Solar Cells for the Aircraft Method

The aircraft solar cell calibration method has provided cells calibrated to space conditions for 37 years. However, it is susceptible to systematic errors due to ozone concentrations in the stratosphere. The present correction procedure applies a 1 percent increase to the measured I(sub SC) values. High band-gap cells are more sensitive to ozone absorbed wavelengths (0.4 to 0.8 microns) so it becomes important to reassess the correction technique. This paper evaluates the ozone correction to be 1+O3xFo, where O3 is the total ozone along the optical path, and Fo is 29.8 x 10(exp -6)/du for a Silicon solar cell, 42.6 x 10(exp -6)/du for a GaAs cell and 57.2 x 10(exp -6)/du for an InGaP cell. These correction factors work best to correct data points obtained during the flight rather than as a correction to the final result.

Snyder, David B.↗

Historical Precision of an Ozone Correction Procedure for AM0 Solar Cell Calibration

In an effort to improve the accuracy of the high altitude aircraft method for calibration of high band-gap solar cells, the ozone correction procedure has been revisited. The new procedure adjusts the measured short circuit current, Isc, according to satellite based ozone measurements and a model of the atmospheric ozone profile then extrapolates the measurements to air mass zero, AMO. The purpose of this paper is to assess the precision of the revised procedure by applying it to historical data sets. The average Isc of a silicon cell for a flying season increased 0.5% and the standard deviation improved from 0.5% to 0.3%. The 12 year average Isc of a GaAs cell increased 1% and the standard deviation improved from 0.8% to 0.5%. The slight increase in measured Isc and improvement in standard deviation suggests that the accuracy of the aircraft method may improve from 1% to nearly 0.5%.

Snyder, David B.↗

High-efficiency heteroepitaxial solar cells for space power applications

The experimental results for several technical approaches aimed at achieving highly efficient solar cells for space-power applications are reported. Efficiencies of up to 24.5 percent (170X, AM0) and 21.7 percent (1X, AM0) have been achieved with homoepitaxial GaAs p/n cells. This one-sun AM0 efficiency value is believed to be the highest reported to date. Tandem solar cells utilizing GaAs-on-Ge structures have been fabricated and shown to have efficiencies up to 21.3 percent (1X, AM0), and a GaAs-on-Si cell at 15.2 percent (1X, AM0) is reported. Homoepitaxial n/p InP cells with an efficiency of 18.8 percent (1X, AM0) are also reported. The fabrication of heteroepitaxial InP solar cells with one-sun AM0 efficiency values of 9.4 percent (on GaAs) and 7.2 percent (on Si) is described.

Vernon, S. M.↗

Diffusion lengths in irradiated N/P InP-on-Si solar cells

Indium phosphide (InP) solar cells were made on silicon (Si) wafers (InP/Si) by to take advantage of both the radiation-hardness properties of the InP solar cell and the light weight and low cost of Si wafers. The InP/Si cell application is for long duration and/or high radiation orbit space missions. Spire has made N/P InP/Si cells of sizes up to 2 cm by 4 cm with beginning-of-life (BOL) AM0 efficiencies over 13% (one-sun, 28C). These InP/Si cells have higher absolute efficiency and power density after a high radiation dose than gallium arsenide (GaAs) or silicon (Si) solar cells after a fluence of about 2e15 1 MeV electrons/sq. cm. In this work, we investigate the minority carrier (electron) base diffusion lengths in the N/P InP/Si cells. A quantum efficiency model was constructed for a 12% BOL AM0 N/P InP/Si cell which agreed well with the absolutely measured quantum efficiency and the sun-simulator measured AM0 photocurrent (30.1 mA/sq. cm). This model was then used to generate a table of AM0 photocurrents for a range of base diffusion lengths. AM0 photocurrents were then measured for irradiations up to 7.7e16 1 MeV electrons/sq. cm (the 12% BOL cell was 8% after the final irradiation). By comparing the measured photocurrents with the predicted photocurrents, base diffusion lengths were assigned at each fluence level. A damage coefficient K of 4e-8 and a starting (unirradiated) base electron diffusion length of 0.8 microns fits the data well. The quantum efficiency was measured again at the end of the experiment to verify that the photocurrent predicted by the model (25.5 mA/sq. cm) agreed with the simulator-measured photocurrent after irradiation (25.7 mA/sq. cm).

Wojtczuk, Steven↗

AlGaAs top solar cell for mechanical attachment in a multi-junction tandem concentrator solar cell stack

Free-standing, transparent, tunable bandgap AlxGa1-xAs top solar cells have been fabricated for mechanical attachment in a four terminal tandem stack solar cell. Evaluation of the device results has demonstrated 1.80 eV top solar cells with efficiencies of 18 percent (100 X, and AM0) which would yield stack efficiencies of 31 percent (100 X, AM0) with a silicon bottom cell. When fully developed, the AlxGa1-xAs/Si mechanically-stacked two-junction solar cell concentrator system can provide efficiencies of 36 percent (AM0, 100 X). AlxGa1-xAs top solar cells with bandgaps from 1.66 eV to 2.08 eV have been fabricated. Liquid phase epitaxy (LPE) growth techniques have been used and LPE has been found to yield superior AlxGa1-xAs material when compared to molecular beam epitaxy and metal-organic chemical vapor deposition. It is projected that stack assembly technology will be readily applicable to any mechanically stacked multijunction (MSMJ) system. Development of a wide bandgap top solar cell is the only feasible method for obtaining stack efficiencies greater than 40 percent at AM0. System efficiencies of greater than 40 percent can be realized when the AlGaAs top solar cell is used in a three solar cell mechanical stack.

Dinetta, L. C.↗