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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Flat-plate solar array project. Volume 4: High-efficiency solar cells

The High Efficiency Solar Cell Task was assigned the objective of understanding and developing high efficiency solar cell devices that would meet the cost and performance goals of the Flat Plate Solar Array (FSA) Project. The need for research dealing with high efficiency devices was considered important because of the role efficiency plays in reducing price per watt of generated energy. The R&D efforts conducted during the 1982 to 1986 period are summarized to provide understanding and control of energy conversion losses associated with crystalline silicon solar cells. New levels of conversion efficiency were demonstrated. Major contributions were made both to the understanding and reduction of bulk and surface losses in solar cells. For example, oxides, nitrides, and polysilicon were all shown to be potentially useful surface passivants. Improvements in measurement techniques were made and Auger coefficients and spectral absorption data were obtained for unique types of silicon sheets. New modelling software was developed including a program to optimize a device design based on input characteristics of a cell.

Leipold, M.↗
NASA NTRS1971

Silicon solar cells as a high-solar-intensity radiometer

The characteristics of a conventional, 1- by 2-cm, N/P, gridded silicon solar cell when used as a radiometer have been determined for solar intensity levels to 2800 mW/sq cm (20 solar constants). The short-circuit current was proportional to the radiant intensity for levels only to 700 mW/sq cm (5 solar constants). For intensity levels greater than 700 mW/sq cm, it was necessary to operate the cell in a photoconductive mode in order to obtain a linear relation between the measured current and the radiant intensity. When the solar cell was biased with a reverse voltage of -1 V, the measured current and radiant intensity were linearly related over the complete intensity range from 100 to 2800 mW/sq cm.

Spisz, E. W.↗
NASA NTRS1972

Development of GaAs solar cells

Calculations of GaAs solar cell output parameters were refined and a computer model was developed for parameter optimization. The results were analyzed to determine the material characteristics required for a high efficiency solar cell. Calculated efficiencies for a P/N cell polarity are higher than an N/P cell. Both cell polarities show efficiency to have a larger dependence on short circuit current than an open circuit voltage under nearly all conditions considered. The tolerances and requirements of a cell fabrication process are more critical for an N/P type than for a P/N type cell. Several solar cell fabrication considerations relative to junction formation using ion implantation are also discussed.

Mcnally, P. J.↗
NASA NTRS1993

Generating AC With Rotating Solar Cells

Rotating solar photovoltaic cells or batteries connected to suitable mechanical and/or electronic commutators produce nearly sinusoidal alternating current. Eliminates need for inverter circuitry and its attendant power-consumption and heat-dissipation problems, but imposes need for low-power-consumption rotary mechanism. Intended for use aboard spacecraft, also useful in special terrestrial situations where solar electric power must be transmitted over powerlines from one remote location to another.

Flanagan, David T.↗
NASA NTRS1981

Effects of low temperature periodic annealing on the deep-level defects in 200 keV proton irradiated AlGaAs-GaAs solar cells

The GaAs solar cell has shown good potential for space applications. However, degradation in performance occurred when the cells were irradiated by high energy electrons and protons in the space environment. The considered investigation is concerned with the effect of periodic thermal annealing on the deep-level defects induced by the 200 keV protons in the AlGaAs-GaAs solar cells. Protons at a fluence of 10 to the 11th P/sq cm were used in the irradiation cycle, while annealing temperatures of 200 C (for 24 hours), 300 C (six hours), and 400 C (six hours) were employed. The most likely candidate for the E(c) -0.71 eV electron trap observed in the 200 keV proton irradiated samples may be due to GaAs antisite, while the observed E(v) +0.18 eV hole trap has been attributed to the gallium vacancy related defect. The obtained results show that periodic annealing in the considered case does not offer any advantages over the one time annealing process.

Li, S. S.↗
NASA NTRS1987

Results of 1 MeV proton irradiation of front and back surfaces of silicon solar cells

Several silicon solar cells with and without back surface fields (BSF), having thicknesses of 200 microns and 63 microns were irradiated with 1 MeV protons having fluences between 1 times 10 to the 10th power and 1 times 10 to the 12th power p/square cm. The irradiation was performed using both normal and isotropic incidence on the front as well as back surfaces of the solar cells. The results of the back surface irradiations are analyzed using a model in which irradiation induced defects across the high-low (BSF) junction are considered. It is concluded that degradation of the high-low junction is responsible for the severe performance loss in thinner cells when irradiated from the rear.

Anspaugh, B. E.↗
DOE OSTI2023

Synthesizing and formulating metal oxide nanoparticle inks for perovskite solar cells

The perovskite solar cell has commercial potential due to the low-cost of materials and manufacturing processes with cell efficiencies on par with traditional technologies. Nanomaterials have many properties that make them attractive for the perovskite devices, including low-cost inks, low temperature processing, stable material properties and good charge transport. In this feature article, the use of nanomaterials in the hole transport and electron transport layers are reviewed. Specifically, SnO 2 and NiO x are the leading materials with the most promise for translation to large scale applications. Here, the review includes a discussion of the synthesis, formulation, and processing of these nanoparticles and provides insights for their further deployment towards commercially viable perovskite solar cells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1980

Effects of grain boundaries in polycrystalline solar cells

In polycrystalline solar cells, the short-circuit current is reduced (compared to single-crystal cells) due to recombination of minority carriers at the grain boundaries. The magnitude of this reduction is calculated for the case of a monochromatic beam of light, assuming that both the light beam and the grain boundaries are perpendicular to a p-n junction. The photoresponse of the junction is calculated in terms of the absorption coefficient of the light, the minority-carrier diffusion length, the surface recombination velocity at the grain boundary and the distance of the light beam from the grain boundary. The analysis gives an expression for an effective grain boundary width which depends on wavelength. This width determines the reduction in short-circuit current of solar cells made from material with columnar-type grains.

Zook, J. D.↗
NASA NTRS1991

Effect of InAlAs window layer on the efficiency of indium phosphide solar cells

Indium phosphide (InP) solar cell efficiencies are limited by surface recombination. The effect of a wide-bandgap lattice-matched indium aluminum arsenide (In0.52Al0.48As) window layer on the performance of InP solar cells was investigated using a numerical code PC-1D. The p(+)n InP solar cell performance improves significantly with the use of a window layer. No improvement is seen for n(+)p InP cells. Cell results are explained by the band diagram of the heterostructure and the conduction-band energy discontinuity. The calculated I-V and internal quantum efficiency results clearly demonstrate that In0.52Al0.48As is a promising candidate as a window layer material for p(+)n InP solar cells.

Jain, R. K.↗
DOE OSTI2020

Thermodynamic Properties and Molecular Packing Explain Performance and Processing Procedures of Three D18:NFA Organic Solar Cells

Abstract Organic solar cells (OSCs) based on D18:Y6 have recently exhibited a record power conversion efficiency of over 18%. The initial work is extended and the device performance of D18‐based OSCs is compared with three non‐fullerene acceptors, Y6, IT‐4F, and IEICO‐4Cl, and their molecular packing characteristics and miscibility are studied. The D18 polymer shows unusually strong chain extension and excellent backbone ordering in all films, which likely contributes to the excellent hole‐transporting properties. Thermodynamic characterization indicates a room‐temperature miscibility for D18:Y6 and D18:IT‐4F near the percolation threshold. This corresponds to an ideal quench depth and explains the use of solvent vapor annealing rather than thermal annealing. In contrast, D18:IEICO‐4Cl is a low‐miscibility system with a deep quench depth during casting and poor morphology control and low performance. A failure of ternary blends with PC 71 BM is likely due to the near‐ideal miscibility of Y6 to begin with and indicates that strategies for developing successful ternary or quaternary solar cells are likely very different for D18 than for other high‐performing donors. This work reveals several unique property–performance relations of D18‐based photovoltaic devices and helps guide design or fabrication of yet higher efficiency OSCs.

Wang, Zhen↗
NASA NTRS1991

The effect of process conditions on the performance of epitaxial InP solar cells

Indium phosphide solar cells have a higher resistance to electron irradiation than Si or GaAs cells of comparable junction depth. As a result, there is much interest in the use of this material for space applications. Cells of this material were made in bulk InP by a number of techniques, including ion implantation, direct diffusion in sealed ampoules, and by open tube diffusion. However, it is generally considered that the epitaxial approach will be superior to all of these techniques. The epitaxy of InP is considerably more difficult than that of gallium arsenide, for a number of reasons. Perhaps the most important is the fact that the native oxides of Indium are extremely difficult to remove, as compared to that of Gallium. In addition, thermal treatments for the desorption of these oxides often result in the formation of phosphorus vacancies and free indium on the surface. Thus, inadequate sample preparation before epitaxy, poor reactor cleaning procedures, or poor transition procedures between the growth of successive layers, all give rise to trap phenomena and to high interface recombination velocities. Moreover, the lifetime of the grown material is dominated by the occurrence of native defects, so that it is a strong function of growth parameters. These problems are of special interest to the fabrication of solar cells, where long life-time, combined with the absence of traps, is highly desirable. A study of this problem is described using a non-invasive diagnostic technique which was developed.

Borrego, J. M.↗
NASA NTRS1992

Effect of InAlAs window layer on efficiency of indium phosphide solar cells

Indium phosphide (InP) solar cell efficiencies are limited by surface recombination. The effect of a wide bandgap, lattice-matched indium aluminum arsenide (In(0.52)Al(0.48)As) window layer on the performance of InP solar cells was investigated by using the numerical code PC-1D. The p(+)n InP solar cell performance improved significantly with the use of the window layer. No improvement was seen for the n(+)p InP cells. The cell results were explained by the band diagram of the heterostructure and the conduction band energy discontinuity. The calculated current voltage and internal quantum efficiency results clearly demonstrated that In(0.52)Al(0.48)As is a very promising candidate for a window layer material for p(+)n InP solar cells.

Jain, Raj K.↗
DOE OSTI2022

Quantum-size-tuned heterostructures enable efficient and stable inverted perovskite solar cells

The energy landscape of reduced-dimensional perovskites (RDPs) can be tailored by adjusting their layer width (n). Recently, 2D/3D heterostructures containing n = 1 and 2 RDPs have produced PSCs with > 25% power conversion efficiency (PCE). Unfortunately, this method does not translate to inverted PSCs due to electron blocking at the 2D/3D interface. Here we report a method to increase the layer width of RDPs in 2D/3D heterostructures in order to address this problem. We discover that bulkier organics form 2D heterostructures more slowly, resulting in wider RDPs; and that small modifications to ligand design induce preferential growth of n ≥ 3 RDPs. Levering these insights, we developed efficient inverted PSCs (certified 23.91% quasi-steady state efficiency). Furthermore, unencapsulated devices operate at room temperature and ~50% relative humidity for over 1000 hrs without loss of PCE; and, when subjected to ISOS-L3 accelerated aging encapsulated devices retain 92% of PCE after 500 hrs.

14 SOLAR ENERGY↗
NASA NTRS1991

Annealing characteristics of irradiated hydrogenated amorphous silicon solar cells

It was shown that 1 MeV proton irradiation with fluences of 1.25E14 and 1.25E15/sq cm reduces the normalized I(sub SC) of a-Si:H solar cell. Solar cells recently fabricated showed superior radiation tolerance compared with cells fabricated four years ago; the improvement is probably due to the fact that the new cells are thinner and fabricated from improved materials. Room temperature annealing was observed for the first time in both new and old cells. New cells anneal at a faster rate than old cells for the same fluence. From the annealing work it is apparent that there are at least two types of defects and/or annealing mechanisms. One cell had improved I-V characteristics following irradiation as compared to the virgin cell. The work shows that the photothermal deflection spectroscopy (PDS) and annealing measurements may be used to predict the qualitative behavior of a-Si:H solar cells. It was anticipated that the modeling work will quantitatively link thin film measurements with solar cell properties. Quantitative predictions of the operation of a-Si:H solar cells in a space environment will require a knowledge of the defect creation mechanisms, defect structures, role of defects on degradation, and defect passivation and annealing mechanisms. The engineering data and knowledge base for justifying space flight testing of a-Si:H alloy based solar cells is being developed.

Payson, J. S.↗
NASA NTRS1995

Space qualification of IR-reflecting coverslides for GaAs solar cells

Improvements to GaAs solar array performance, from the use on solar cell coverslides of several reflecting coatings that reject unusable portions of the solar spectrum, are quantified. Blue-red-rejection (BRR) coverslides provide both infrared reflection (IRR) and ultraviolet rejection (UVR). BRR coverslides were compared to conventional antireflection (AR) and ultraviolet (UV) coated coverslides. A 2% improvement in peak-power output, relative to that from Ar-coated coverslides, is seen for cells utilizing BRR coverslides with the widest bandpass. Coverslide BRR-filter bandpass width and covered-solar-cell short-circuit current is a function of incident light angle and the observed narrower-bandpass filters are more sensitive to change in angle from the normal than are wide-bandpass filters. The first long-term (3000 hours) UV testing of unirradiated and 1 MeV electron-irradiated GaAs solar cells, with multilayer-coated coverslides to reduce solar array operating temperature, has indicated that all multilayer coatings on coverslides and solar cells will experience degradation from the space environment (UV and/or electrons). Five types of coverslide coatings, designed for GaAs solar cells, were tested as part of a NASA-sponsored space-flight qualification for BRR, multi-layer-coated, coverslides. The reponse to the different radiations varied with the coatings. The extent of degradation and its consequences on the solar cell electrical characteristics depend upon the coatings and the radiation. In some cases, an improved optical coupling was observed during long-term UV exposure to the optical stack. The benefits of multi-layered solar cell optics may depend upon both the duration and the radiation environment of a mission.

Meulenberg, Andrew↗
NASA NTRS1976

Solar cell array design handbook, volume 1

Twelve chapters discuss the following: historical developments, the environment and its effects, solar cells, solar cell filters and covers, solar cell and other electrical interconnections, blocking and shunt diodes, substrates and deployment mechanisms, material properties, design synthesis and optimization, design analysis, procurement, production and cost aspects, evaluation and test, orbital performance, and illustrative design examples. A comprehensive index permits rapid locating of desired topics. The handbook consists of two volumes: Volume 1 is of an expository nature while Volume 2 contains detailed design data in an appendix-like fashion. Volume 2 includes solar cell performance data, applicable unit conversion factors and physical constants, and mechanical, electrical, thermal optical, magnetic, and outgassing material properties. Extensive references are provided.

Rauschenbach, H. S.↗
NASA NTRS1984

Automated assembly of Gallium Arsenide and 50-micron thick silicon solar cell modules

The TRW automated solar array assembly equipment was used for the module assembly of 300 GaAs solar cells and 300 50 micron thick silicon solar cells (2 x 4 cm in size). These cells were interconnected with silver plated Invar tabs by means of welding. The GaAs cells were bonded to Kapton graphite aluminum honeycomb graphite substrates and the thin silicon cells were bonded to 0.002 inch thick single layer Kapton substrates. The GaAs solar cell module assembly resulted in a yield of 86% and the thin cell assembly produced a yield of 46% due to intermittent sticking of weld electrodes during the front cell contact welding operation. (Previously assembled thin cell solar modules produced an overall assembly yield of greater than 80%).

Mesch, H. G.↗