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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 sources NASA NTRS DOE OSTI

NASA NTRS1991

Thin, Lightweight Solar Cell

Improved design for thin, lightweight solar photovoltaic cells with front contacts reduces degradation of electrical output under exposure to energetic charged particles (protons and electrons). Increases ability of cells to maintain structural integrity under exposure to ultraviolet radiation by eliminating ultraviolet-degradable adhesives used to retain cover glasses. Interdigitated front contacts and front junctions formed on semiconductor substrate. Mating contacts formed on back surface of cover glass. Cover glass and substrate electrostatically bonded together.

Brandhorst, Henry W., Jr.↗

NASA NTRS1991

Thin solar cell and lightweight array

A thin, lightweight solar cell that utilizes front contact metallization is presented. Both the front light receiving surface of the solar cell and the facing surface of the cover glass are recessed to accommodate this metallization. This enables the two surfaces to meet flush for an optimum seal.

Brandhorst, Henry W., Jr.↗

NASA NTRS1991

A very low resistance, non-sintered contact system for use on indium phosphide concentrator/shallow junction solar cells

An investigation is made into the possibility of providing low resistance contacts to shallow junction InP solar cells which do not require sintering and which do not cause device degradation even when subjected to extended annealing at elevated temperatures. We show that the addition of In to Au contacts in amounts that exceed the solid solubility limit lowers the as-fabricated (unsintered) contact resistivity (R sub c) to the 10(exp -5) ohm cm(exp 2) range. We next consider the contact system Au/Au2P3, which has been shown to exhibit as-fabricated R sub c values in the 10(exp -6) ohm cm(exp 2) range, but which fails quickly when heated. We show that the substitution of a refractory metal (W, Ta) for Au preserves the low R sub c values while preventing the destructive reactions that would normally take place in this system at high temperatures. We show, finally, that R sub c values in the 10(exp -7) ohm cm(exp 2) range can be achieved without sintering by combining the effects of In or Ga additions to Au contacts with the effects of introducing a thin Au2P3 layer at the metal-InP interface.

Weizer, Victor G.↗

NASA NTRS1991

A very low resistance, non-sintered contact system for use on indium phosphide concentrator/shallow junction solar cells

An investigation is made into the possibility of providing low resistance contacts to shallow junction InP solar cells which do not require sintering and which do not cause device degradation even when subjected to extended annealing at elevated temperatures. We show that the addition of In to Au contacts in amounts that exceed the solid solubility limit lowers the as-fabricated (unsintered) contact resistivity (R sub c) to the 10(exp -5) ohm cm(exp 2) range. We next consider the contact system Au/Au2P3 which has been shown to exhibit as-fabricated R sub c values in the 10(exp -6) ohm cm(exp 2) range, but which fails quickly when heated. We show that the substitution of a refractory metal (W, Ta) for Au preserves the low R sub c values while preventing the destructive reactions that would normally take place in this system at high temperatures. We show, finally, that R sub c values in the 10(exp -7) ohm cm(exp 2) range can be achieved without sintering by combining the effects of In or Ga additions to Au contacts with the effects of introducing a thin Au2P3 layer at the metal-InP interface.

Weizer, Victor G.↗

NASA NTRS1995

Thrust measurement in a 2-D scramjet nozzle

The two-dimensional thrust nozzle presents a challenging problem. The loading is not axisymmetric as in the case of a cone and the internal flow presents some design difficulties. A two-sting system has been chosen to accomodate the internal flow and achieve some symmetry. The situation is complicated by the fact that with the small ramp angle and the internal pressure on the nozzle walls, loading is predominantly transverse. Yet it is the axial thrust which is to be measured (i.e., the tensile waves propagating in the stings). Although bending stress waves travel at most at only 60% of the speed of the axial stress waves, the system needs to be stiffened against bending. The second sting was originally only used to preserve symmetry. However, the pressures on each thrust surface may be quite different at some conditions, so at this stage the signals from both stings are being averaged as a first order approximation of the net thrust. The expected axial thrust from this nozzle is not large so thin stings are required. In addition, the contact area between nozzle and sting needs to be maximized. The result was that it was decided to twist the stings through 90 deg, without distorting their cross-sectional shape, just aft of the nozzle. Finite element analysis showed that this would not significantly alter the propagation of the axial stress wave in the sting, while the rigidity of the system is greatly increased. A Mach 4 contoured nozzle is used in the experiments. The thrust calculated by integrating the static pressure measurements on the thrust surfaces is compared with the deconvolved strain measurement of the net thrust for the cases of air only and hydrogen fuel injected into air at approximately 9 MJ/kg nozzle supply enthalpy. The gain in thrust due to combustion is visible in this result.

Tuttle, Sean↗

NASA NTRS2003

Evidence for a Second Generation of Magnesite in Martian Meteorite Allan Hills 84001

Single-stage formation mechanisms for carbonate and other secondary minerals in ALH84001 are rapidly being revised to include multiple stages of carbonate growth and later thermal and mechanical events including alteration. In an effort to confirm some of these more complex histories we have been studying carbonate-bearing regions within this meteorite. Magnesitic carbonates found in contact with unique 'slab' carbonates in two thin sections of ALH84001 show indications of being of a later generation. The results of our observations help clarify the origins of the carbonate and related minerals in ALH84001, and how these minerals can be used to understand the history of interactions between the martian crust and its volatile inventory.

Corrigan, C. M.↗

NASA NTRS1988

A hydroponic system for microgravity plant experiments

The construction of a permanently manned space station will provide the opportunity to grow plants for weeks or months in orbit for experiments or food production. With this opportunity comes the need for a method to provide plants with a continuous supply of water and nutrients in microgravity. The Capillary Effect Root Environment System (CERES) uses capillary forces to maintain control of circulating plant nutrient solution in the weightless environment of an orbiting spacecraft. The nutrient solution is maintained at a pressure slightly less than the ambient air pressure while it flows on one side of a porous membrane. The root, on the other side of the membrane, is surrounded by a thin film of nutrient solution where it contacts the moist surface of the membrane. The root is provided with water, nutrients and air simultaneously. Air bubbles in the nutrient solution are removed using a hydrophobic/hydrophilic membrane system. A model scaled to the size necessary for flight hardware to test CERES in the space shuttle was constructed.

short duration↗

NASA NTRS1993

Quality Factor and Microslipping of Fatigue Cracks in Thin Plates at Resonant Vibration

Resonant vibrations have been stimulated in thin metal plates using a non-contacting electromagnetic driver. A sinusoidal force was applied in a swept frequency fashion and the resulting surface displacements were monitored through the use of an acoustic microphone. It has been found that the presence of a fatigue crack in the sample causes a broadening of the second resonance peak. The Q factors of the resonance curves were determined and are directly correlated with the presence of fatigue cracks in the samples. The broadening of the curves is explained in terms of a microslipping at the crack face walls which reduces the amplitude of the resonant vibration by increasing the damping of the system. A comparison is made between the resonance characteristics of fatigue damaged and notched samples, where the stiffness of the two systems is nearly constant while the interaction between crack face walls is eliminated in the latter.

Wincheski, B.↗

NASA NTRS2011

Improved Rare-Earth Emitter Hollow Cathode

An improvement has been made to the design of the hollow cathode geometry that was created for the rare-earth electron emitter described in Compact Rare Earth Emitter Hollow Cathode (NPO-44923), NASA Tech Briefs, Vol. 34, No. 3 (March 2010), p. 52. The original interior assembly was made entirely of graphite in order to be compatible with the LaB6 material, which cannot be touched by metals during operation due to boron diffusion causing embrittlement issues in high-temperature refractory materials. Also, the graphite tube was difficult to machine and was subject to vibration-induced fracturing. This innovation replaces the graphite tube with one made out of refractory metal that is relatively easy to manufacture. The cathode support tube is made of molybdenum or molybdenum-rhenium. This material is easily gun-bored to near the tolerances required, and finish machined with steps at each end that capture the orifice plate and the mounting flange. This provides the manufacturability and robustness needed for flight applications, and eliminates the need for expensive e-beam welding used in prior cathodes. The LaB6 insert is protected from direct contact with the refractory metal tube by thin, graphite sleeves in a cup-arrangement around the ends of the insert. The sleeves, insert, and orifice plate are held in place by a ceramic spacer and tungsten spring inserted inside the tube. To heat the cathode, an insulating tube is slipped around the refractory metal hollow tube, which can be made of high-temperature materials like boron nitride or aluminum nitride. A screw-shaped slot, or series of slots, is machined in the outside of the ceramic tube to constrain a refractory metal wire wound inside the slot that is used as the heater. The screw slot can hold a single heater wire that is then connected to the front of the cathode tube by tack-welding to complete the electrical circuit, or it can be a double slot that takes a bifilar wound heater with both leads coming out the back. This configuration replaces the previous sheathed heater design that limited the cycling-life of the cathode.

Goebel, Dan M.↗

DOE OSTI2021

Submicron Thickness Characterization of Poly-Si Thin Films on Textured Surfaces by X-Ray Diffraction for Minimizing Parasitic Absorption in Poly-Si/SiO2 Passivating Contact Cells

Poly-Si/SiO2 passivating contacts have shown great potential for industry-relevant next-generation solar cells. Previous work has demonstrated an improved Jsc from dry reactive ion etching in an SF6 environment, using front metal grids as a self-aligned mask. Here, we show an effective method to measure the front poly-Si thickness on an alkaline textured surface using X-ray diffraction. The calculated thicknesses are compared with cross-section SEM analysis and Quokka simulation. We show that by thinning the front poly-Si from 200 nm to 60 nm, Jsc increases by 2.4 mA/cm2, leading to an absolute efficiency gain of 1.73%. Finally, we discuss possible reasons for the premature loss of passivation before the removal of all poly-Si.

41 EE - Solar Energy Technologies Office (EE-4S)↗

NASA NTRS2007

Flexible carbon-based ohmic contacts for organic transistors

The present invention relates to a system and method of organic thin-film transistors (OTFTs). More specifically, the present invention relates to employing a flexible, conductive particle-polymer composite material for ohmic contacts (i.e. drain and source).

Brandon, Erik↗

DOE OSTI2023

Edge Channel Transmission through a Quantum Point Contact in the Two-Dimensional Topological Insulator Cadmium Arsenide

Cadmium arsenide (Cd 3 As 2 ) thin films feature a two-dimensional topological insulator (2D TI) phase for certain thicknesses, which theoretically hosts a set of counterpropagating helical edge states that are characteristic of a quantum spin Hall (QSH) insulator. In devices containing electrostatically defined junctions and for magnetic fields below a critical value, chiral edge modes of the quantum Hall effect can coexist with QSH-like edge modes. In this work, we use a quantum point contact (QPC) device to characterize edge modes in the 2D TI phase of Cd 3 As 2 and to understand how they can be controllably transmitted, which is important for use in future quantum interference devices. We investigate equilibration among both types of modes and find non-spin-selective equilibration. We also demonstrate the effect of the magnetic field on suppressing equilibration. We discuss the potential role of QSH-like modes in a transmission pathway that precludes full pinch-off.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2020

Highly Efficient and Stable Perovskite Solar Cells Enabled by Low‐Cost Industrial Organic Pigment Coating

Abstract Surface passivation of perovskite solar cells (PSCs) using a low‐cost industrial organic pigment quinacridone (QA) is presented. The procedure involves solution processing a soluble derivative of QA, N , N ‐bis(tert‐butyloxycarbonyl)‐quinacridone (TBOC‐QA), followed by thermal annealing to convert TBOC‐QA into insoluble QA. With halide perovskite thin films coated by QA, PSCs based on methylammonium lead iodide (MAPbI 3 ) showed significantly improved performance with remarkable stability. A PCE of 21.1 % was achieved, which is much higher than 18.9 % recorded for the unmodified devices. The QA coating with exceptional insolubility and hydrophobicity also led to greatly enhanced contact angle from 35.6° for the pristine MAPbI 3 thin films to 77.2° for QA coated MAPbI 3 thin films. The stability of QA passivated MAPbI 3 perovskite thin films and PSCs were significantly enhanced, retaining about 90 % of the initial efficiencies after more than 1000 hours storage under ambient conditions.

He, Qingquan↗

DOE OSTI2020

Highly Efficient and Stable Perovskite Solar Cells Enabled by Low‐Cost Industrial Organic Pigment Coating

He, Qingquan↗

DOE OSTI2020

Thin film CZTSSe photovoltaic device

A method for forming a back contact on an absorber layer in a photovoltaic device includes forming a two dimensional material on a first substrate. An absorber layer including Cu—Zn—Sn—S(Se) (CZTSSe) is grown over the first substrate on the two dimensional material. A buffer layer is grown on the absorber layer on a side opposite the two dimensional material. The absorber layer is exfoliated from the two dimensional material to remove the first substrate from a backside of the absorber layer opposite the buffer layer. A back contact is deposited on the absorber layer.

14 SOLAR ENERGY↗

NASA NTRS1984

Amorphous metallic films in silicon metallization systems

The general objective was to determine the potential of amorphous metallic thin films as a means of improving the stability of metallic contacts to a silicon substrate. The specific objective pursued was to determine the role of nitrogen in the formation and the resulting properties of amorphous thin-film diffusion barriers. Amorphous metallic films are attractive as diffusion barriers because of the low atomic diffusivity in these materials. Previous investigations revealed that in meeting this condition alone, good diffusion barriers are not necessarily obtained, because amorphous films can react with an adjacent medium (e.g., Si, Al) before they recrystallize. In the case of a silicon single-crystalline substrate, correlation exists between the temperature at which an amorphous metallic binary thin film reacts and the temperatures at which the films made of the same two metallic elements react individually. Amorphous binary films made of Zr and W were investigated. Both react with Si individually only at elevated temperatures. It was confirmed that such films react with Si only above 700 C when annealed in vacuum for 30 min. Amorphous W-N films were also investigated. They are more stable as barriers between Al and Si than polycrystalline W. Nitrogen effectively prevents the W-Al reaction that sets in at 500 C with polycrystalline W.

Nicolet, M. A.↗

NASA NTRS2011

Mount Protects Thin-Walled Glass or Ceramic Tubes from Large Thermal and Vibration Loads

The design allows for the low-stress mounting of fragile objects, like thin walled glass, by using particular ways of compensating, isolating, or releasing the coefficient of thermal expansion (CTE) differences between the mounted object and the mount itself. This mount profile is lower than true full kinematic mounting. Also, this approach enables accurate positioning of the component for electrical and optical interfaces. It avoids the higher and unpredictable stress issues that often result from potting the object. The mount has been built and tested to space-flight specifications, and has been used for fiber-optic, optical, and electrical interfaces for a spaceflight mission. This mount design is often metal and is slightly larger than the object to be mounted. The objects are optical or optical/electrical, and optical and/or electrical interfaces are required from the top and bottom. This requires the mount to be open at both ends, and for the object s position to be controlled. Thin inside inserts at the top and bottom contact the housing at defined lips, or edges, and hold the fragile object in the mount. The inserts can be customized to mimic the outer surface of the object, which further reduces stress. The inserts have the opposite CTE of the housing material, partially compensating for the CTE difference that causes thermal stress. A spring washer is inserted at one end to compensate for more CTE difference and to hold the object against the location edge of the mount for any optical position requirements. The spring also ensures that any fiber-optic or optic interface, which often requires some pressure to ensure a good interface, does not overstress the fragile object. The insert thickness, material, and spring washer size can be traded against each other to optimize the mount and stresses for various thermal and vibration load ranges and other mounting requirements. The alternate design uses two separate, unique features to reduce stress and hold the object. A release agent is applied to the inside surface of the mount just before the binding potting material is injected in the mount. This prevents the potting material from bonding to the mount, and thus prevents stress from being applied, at very low temperatures, to the fragile object being mounted. The potting material mixing and curing is temperature- and humidity-controlled. The mount has radial grooves cut in it that the potting material fills, thus controlling the vertical position of the mounted object. The design can easily be used for long and thin objects, short and wide objects, and any shape in between. The design s advantages are amplified for long and thin fragile objects. The general testing range was 45 to +45 C, but multiple mounts were successfully tested down to 60 and up to 50 C and the design can be adjusted for larger ranges.

Amato, Michael↗

DOE OSTI2021

Visualizing Intrinsic 3D-Strain Distribution in Gold Coated ZnO Microstructures by Bragg Coherent X-Ray Diffraction Imaging and Transmission Electron Microscopy with Respect to Piezotronic Applications

Novel devices ranging from bio magnetic field sensors to energy harvesting nano machines utilize the piezotronic effect. For optimal function, understanding the interaction of electrical and strain phenomena within the semiconductor crystal is necessary. Here, studies of a model piezotronic system are presented, consisting of a ZnO microrod coated by a thin layer of gold, which forms a Schottky contact with the piezoelectric ZnO material. Coherent X-ray diffraction imaging (CXDI) and transmission electron microscopy (TEM) are used to visualize the structure and strain distribution, showing that the ZnO microrod exhibits strains of multiple origins in the bulk and at the interface. Strain values of -6 × 10 -4 have been measured by CXDI at the ZnO/Au interface. The origin is shown to be a combination of an interface strain, possibly caused by the Schottky contact formation, and distinct, localized electrical fields inside the crystal which are assigned to electron depletion and screening in a bent ZnO/Au piezotronic rod. These findings will contribute to sensor development and to a better understanding of piezotronic applications.

36 MATERIALS SCIENCE↗