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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Current status of silicon solar cell technology

In quest of higher efficiency, major progress has occurred in solar cell technology. Cell efficiency has climbed about 50 percent. Technical approaches leading to increased output include back surface fields, shallow junctions, improved antireflection coatings, surface texturizing, and fine grid patterns on the cell surface. The status of current solar cell technology and its incorporation into cell production is discussed. Research and development leading to improved performance and reduced cost are also described.

Brandhorst, H. W., Jr.↗
NASA NTRS2004

Integrated Antenna/Solar Array Cell (IA/SAC) System for Flexible Access Communications

Present satellite communications systems normally use separate solar cells and antennas. Since solar cells generally account for the largest surface area of the spacecraft, co-locating the antenna and solar cells on the same substrate opens the possibility for a number of data-rate-enhancing communications link architecture that would have minimal impact on spacecraft weight and size. The idea of integrating printed planar antenna and solar array cells on the same surface has been reported in the literature. The early work merely attempted to demonstrate the feasibility by placing commercial solar cells besides a patch antenna. Recently, Integrating multiple antenna elements and solar cell arrays on the same surface was reported for both space and terrestrial applications. The application of photovoltaic solar cell in a planar antenna structure where the radiating patch antenna is replaced by a Si solar cell has been demonstrated in wireless communication systems (C. Bendel, J. Kirchhof and N. Henze, 3rd Would Photovotaic Congress, Osaka, Japan, May 2003). Based on a hybrid approach, a 6x1 slot array with circularly polarized crossdipole elements co-located on the same surface of the solar cells array has been demonstrated (S. Vaccaro, J. R. Mosig and P. de Maagt, IEEE Trans. Ant. and Propag., Vol. 5 1, No. 8, Aug. 2003). Amorphous silicon solar cells with about 5-10% efficiency were used in these demonstrations. This paper describes recent effort to integrate advanced solar cells with printed planar antennas. Compared to prior art, the proposed WSAC concept is unique in the following ways: 1) Active antenna element will be used to achieve dynamic beam steering; 2) High efficiency (30%) GaAs multi-junction solar cells will be used instead of Si, which has an efficiency of about 15%; 3) Antenna and solar cells are integrated on a common GaAs substrate; and 4) Higher data rate capability. The IA/SAC is designed to operate at X-band (8-12 GH) and higher frequencies Higher operating frequencies enable greater bandwidth and thus higher data transfer rates. The first phase of the effort involves the development of GaAs solar cell MIMs (Monolithically Integrated Module) with a single patch antenna on the opposite side of the substrate. Subsequent work will involve the integration of MIMs and antennas on the same side of the substrate. Results from the phase one efforts will be presented.

Lee, Ricard Q.↗
NASA NTRS2003

Advanced Rainbow Solar Photovoltaic Arrays

Photovoltaic arrays of the rainbow type, equipped with light-concentrator and spectral-beam-splitter optics, have been investigated in a continuing effort to develop lightweight, high-efficiency solar electric power sources. This investigation has contributed to a revival of the concept of the rainbow photovoltaic array, which originated in the 1950s but proved unrealistic at that time because the selection of solar photovoltaic cells was too limited. Advances in the art of photovoltaic cells since that time have rendered the concept more realistic, thereby prompting the present development effort. A rainbow photovoltaic array comprises side-by-side strings of series-connected photovoltaic cells. The cells in each string have the same bandgap, which differs from the bandgaps of the other strings. Hence, each string operates most efficiently in a unique wavelength band determined by its bandgap. To obtain maximum energy-conversion efficiency and to minimize the size and weight of the array for a given sunlight input aperture, the sunlight incident on the aperture is concentrated, then spectrally dispersed onto the photovoltaic array plane, whereon each string of cells is positioned to intercept the light in its wavelength band of most efficient operation. The number of cells in each string is chosen so that the output potentials of all the strings are the same; this makes it possible to connect the strings together in parallel to maximize the output current of the array. According to the original rainbow photovoltaic concept, the concentrated sunlight was to be split into multiple beams by use of an array of dichroic filters designed so that each beam would contain light in one of the desired wavelength bands. The concept has since been modified to provide for dispersion of the spectrum by use of adjacent prisms. A proposal for an advanced version calls for a unitary concentrator/ spectral-beam-splitter optic in the form of a parabolic curved Fresnel-like prism array with panels of photovoltaic cells on two sides (see figure). The surface supporting the solar cells can be adjusted in length or angle to accommodate the incident spectral pattern. An unoptimized prototype assembly containing ten adjacent prisms and three photovoltaic cells with different bandgaps (InGaP2, GaAs, and InGaAs) was constructed to demonstrate feasibility. The actual array will consist of a lightweight thin-film silicon layer of prisms curved into a parabolic shape. In an initial test under illumination of 1 sun at zero airmass, the energy-conversion efficiency of the assembly was found to be 20 percent. Further analysis of the data from this test led to a projected energy conversion efficiency as high as 41 percent for an array of 6 cells or strings (GaP, AlGaAs, InGaP2, GaAs, and two different InGaAs cells or strings).

Mardesich, Nick↗
DOE OSTI2024

Enhanced passivation and stability of negative charge injected SiN x with higher nitrogen content on the boron diffused surface of n-type Si solar cells

This paper explores the potential of the negatively charged SiN x using plasma charge injection technology to passivate the front textured boron-diffused emitter of n-type Si solar cells. The high-x value single SiN x layer with x ≥ 1.30 (x = N/Si) previously developed for the planarized rear-side passivation of p-type silicon solar cells, with an excellent passivation and charge stability, was found to be unacceptable for the passivation on the front textured boron emitter of n-type cells due to a severe bulk lifetime degradation issue. Therefore, in this study, we investigated a new concept of depositing a dual-x SiN x with a low-x SiN x layer (x~1.01) on top of a high-x SiN x layer (x~1.30) for passivation of the front textured rough surface of boron diffused emitter in n-type cells. Here, the optimized dual-x SiN x stack reveals the promise of charge retention for more than 25 years in field operation as well as excellent passivation of boron-doped emitter without bulk lifetime degradation. N-type cells with the optimized dual-x SiN x after charge injection show comparable cell performance to Al 2 O 3 passivated reference cells. The results of cell-level light stability tests using one-cell minimodules exhibit cell performance decay characteristics similar to the traditional Al 2 O 3 /SiN x passivated reference module.

14 SOLAR ENERGY↗
DOE OSTI2021

Exceeding 200 ns Lifetimes in Polycrystalline CdTe Solar Cells

CdTe photovoltaics has achieved one of the lowest levelized costs of electricity among all energy sources. However, for decades, carrier lifetimes have been inferior to those of other prevalent solar cell materials. This quality has inhibited common methods to improve solar cell efficiency such as back-surface fields, electron reflectors, or bifacial solar cells. In this work, a significant increase in carrier lifetime to values exceeding 200 ns in fully functional CdTe solar cells is demonstrated. The increased lifetime is achieved by large CdSeTe grains at the absorber/emitter interface, intragrain passivation in the absorber layer, and chemical passivation by forming nanoscale oxidized tellurium species at the transparent conducting oxide interface. The carrier lifetime is correlated to the open-circuit voltage and enables paths for back-surface manipulation and novel cell architectures to further improve CdTe photovoltaic performance.

14 SOLAR ENERGY↗
NASA NTRS1986

Anticorrosion studies

The aging behavior of chemically bonded interfaces between metals and pottants, such as ethylene vinyl acetate (EVA) was studied using the Dow Corning primer systems. It was observed that the primers seem to function as anticorrosive agents on metal surfaces. It was demonstrated that EVA, and the A-11861 EVA/glass primer stops corrosion of the aluminum used on the back surfaces of crystalline silicon solar cells. However, this same treatment does not work for the aluminum on the back surfaces of amorphous silicon solar cells.

Boerio, J.↗
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 NTRS1983

Ion implanted junctions for silicon space solar cells

This paper reviews the application of ion implantation to emitter and back surface field formation in silicon space solar cells. Experiments based on 2 ohm-cm boron-doped silicon are presented. It is shown that the implantation process is particularly compatible with formation of a high-quality back surface reflector. Large area solar cells with AM0 efficiency greater than 14 percent are reported.

Spitzer, M. B.↗
DOE OSTI2020

Degradation Mechanism Due to Water Ingress Effect on the Top Contact of Cu(In,Ga)Se2 Solar Cells

The impact of moisture ingress on the surface of copper indium gallium diselenide (CIGS) solar cells was studied. While industry-scale modules are encapsulated in specialized polymers and glass, over time, the glass can break and the encapsulant can degrade. During such conditions, water can potentially degrade the interior layers and decrease performance. The first layer the water will come in contact with is the transparent conductive oxide (TCO) layer. To simulate the impact of this moisture ingress, complete devices were immersed in deionized water. To identify the potential sources of degradation, a common window layer for CIGS devices—a bilayer of intrinsic zinc oxide (i-ZnO) and conductive indium tin oxide (ITO)—was deposited. The thin films were then analyzed both pre and post water soaking. To determine the extent of ingress, dynamic secondary ion mass spectroscopy (SIMS) was performed on completed devices to analyze impurity diffusion (predominantly sodium and potassium) in the devices. The results were compared to device measurements, and indicated a degradation of device efficiency (mostly fill factor, contrary to previous studies), potentially due to a modification of the alkali profile.

14 SOLAR ENERGY↗
NASA NTRS1975

Evaluation of silicon ribbon material for solar cell fabrication

Optical microscopy, electron microscopy, and X-ray diffraction were utilized to characterize silicon ribbon structure. Complex twin formation was observed in nearly all ribbons examined. Twins formed in the 110-plane 112-line ribbon orientation appear stable, and this orientation may be preferable when the ribbon is utilized for solar cells. In addition to twinning, grain boundaries and other structural defects were observed in the ribbon material. Hall effect, resistivity, spreading resistance, surface photovoltage, and solar cell electrical/optical measurements were performed on ribbon samples and correlated with structural and ribbon growth characteristics. Only those ribbon samples with either single-crystal structure or with 'parallel' twin formations were capable of solar-cell performance approaching that of Czochralski material.

Leipold, M.↗
NASA NTRS1985

Process and design considerations for high-efficiency solar cells

This paper shows that oxide surface passivation coupled with optimum multilayer anti-reflective coating can provide approx. 3% (absolute) improvement in solar cell efficiency. Use of single-layer AR coating, without passivation, gives cell efficiencies in the range of 15 to 15.5% on high-quality, 4 ohm-cm as well as 0.1 to 0.2 ohm-cm float-zone silicon. Oxide surface passivation alone raises the cell efficiency to or = 17%. An optimum double-layer AR coating on oxide-passivated cells provides an additional approx. 5 to 10% improvement over a single-layer AR-coated cell, resulting in cell efficiencies in excess of 18%. Experimentally observed improvements are supported by model calculations and an approach to or = 20% efficient cells is discussed.

Rohati, A.↗
NASA NTRS1982

Reduction of solar cell efficiency by edge defects across the back-surface-field junction - A developed perimeter model

Material imperfections, impurity clusters and fabrication defects across the back-surface-field junction can degrade the performance of high-efficiency solar cells. The degradation from defects appearing on the circumference of a solar cell is analyzed using a two-region developed perimeter device model. The width of the defective perimeter region is characterized by the range or the distance-of-influence of the defective edge and this width is about two diffusion lengths. The defective edge is characterized by a surface recombination velocity. Family of theoretical curves and numerical examples are presented to show that significant reduction of open-circuit voltage can occur in high-efficiency cells which are thin compared with the diffusion length. In one example, the degradation is decreased from 135 mV to 75 mV when the cell size is increased from 10 to 100 times the diffusion length in a thin cell whose thickness is 1% of the diffusion length.

Sah, C. T.↗
DOE OSTI2022

Modulation of apparent optical properties using arrayed mesoscale structures

In this study, a method for using arrays of mesoscale structures to modify the apparent optical properties of an opaque composite surface has been theoretically demonstrated to both raise and lower the apparent emissivity as compared to the intrinsic properties of the constitutive materials. For design problems where thermomechanical and optical material properties are both of importance, mesoscale surface structuring can greatly expand the design space. Analysis via the net radiosity method herein illustrates the ability to achieve a wide range of spectral apparent optical properties. Notably, a hexagonal array of spheres on a planar surface can raise the apparent emissivity of a planar surface by 50%. Conversely, a hexagonal enclosure of reradiating surfaces, realized by thin adiabatic walls, can reduce the apparent emissivity of a blackbody by half. As this method of modifying apparent optical properties utilizes structures much larger than the wavelengths of interest, the relationship between intrinsic planar emissivity, geometry, and apparent emissivity can be computed semi-analytically at low computational expense. Passive solar cooling, thermophotovoltaic cells, aerodynamic surfaces exposed to intense heating, and solar absorbers are presented as case studies that could benefit from the use of mesoscale structures on opaque surfaces to modify the apparent optical properties.

42 ENGINEERING↗
NASA NTRS1978

Silicon solar cell process. Development, fabrication and analysis

Solar cells were fabricated from unconventional silicon sheets, and the performances were characterized with an emphasis on statistical evaluation. A number of solar cell fabrication processes were used and conversion efficiency was measured under AMO condition at 25 C. Silso solar cells using standard processing showed an average efficiency of about 9.6%. Solar cells with back surface field process showed about the same efficiency as the cells from standard process. Solar cells from grain boundary passivation process did not show any improvements in solar cell performance.

Yoo, H. I.↗
NASA NTRS1981

Silicon solar cells with nickel/solder metallization

The use of nickel plus solder is shown to be feasible for contact metallization for silicon solar cells by offering a relatively inexpensive method of making electrical contact with the cell surfaces. Nickel is plated on silicon solar cells using an electroless chemical deposition method to give contacts with good adhesion, and in some cases where adhesion is poor initially, sintering under relatively mild conditions will dramatically improve the quality of the bond without harming the p-n junction of the cell. The cells can survive terrestrial environment stresses, which is demonstrated by a 1000 hour test at 85 C and 85% relative humidity under constant forward bias of 0.45 volt.

Petersen, R. C.↗
NASA NTRS1986

Passivation of Si solar cells by hetero-epitaxial compound semiconductor coatings

A development status evaluation is made for high efficiency Si solar cells, with emphasis on the suppression of the deleterious effects of surface recombination. ZnS(0.9)Se(0.1) and GaP are identified as candidates for the reduction of surface recombination. Attention is given to methods developed for the deposition of heteroepitaxial compounds designed to block minority carrier transport to the Si solar cell surface without interfering with the majority carrier flow.

Vernon, S. M.↗