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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Experiments On Transparent Conductive Films For Spacecraft

Report describes experiments on thin, transparent, electrically conductive films made, variously, of indium tin oxide covered by magnesium fluoride (ITO/MgF2), aluminum-doped zinc oxide (AZO), or pure zinc oxide (ZnO). Films are candidates for application to such spacecraft components, including various optoelectronic devices and window surfaces that must be protected against buildup of static electric charge. On Earth, such films useful on heat mirrors, optoelectronic devices, gas sensors, and automotive and aircraft windows.

Perez-Davis, Marla E.↗
NASA NTRS2001

Slightly Conductive Transparent Films for Space Applications: Manufacturability and Durability

Highly transparent, slightly conductive films of co-deposited indium tin oxide (ITO) and MgF, have possible applications for environmental protection of exterior surfaces of spacecraft. Reliable preparation of films with the desired sheet resistivity (approximately 10(exp 8) ohms/square) is difficult because the electrical properties of ITO-Mg F, are highly dependent on film composition. We have investigated the use of plasma emission monitoring to improve the reproducibility of films prepared by RF magnetron sputtering. While considerable improve ment was observed, it appears that some in-situ electrical or optica l characterization will be needed for reliable production coating wit h ITO-MgF,. We have also done further evaluation of a possibly undesi rable photoconductive effect previously observed in these films.

Uppala, N.↗
DOE OSTI2019

A Survey of Transparent Conducting Films and Optoelectrical Materials for High Optical Power Applications

The lifetime laser damage performance of a wide range of transparent conductive materials is assessed, including ultrathin metal films, doped metal oxides, doped compound semiconductors, and graphene whose carrier densities span five orders of magnitude from 10 18 to 10 23 cm -3 . Lifetime laser damage thresholds are determined by exposing material surfaces to repeated nanosecond laser pulses at near IR wavelengths (1064 nm). Near threshold fluences, two distinct damage modes, i.e., bulk and discrete, emerge depending on carrier density. These bulk and discrete damage modes are attributed to free carrier-induced bulk and localized, defect-driven absorption processes, respectively. For polycrystalline films with free carrier densities greater than ≈10 20 cm -3 , laser damage thresholds are less than 5 J cm -2 . In contrast, bulk absorption is not apparent at thresholds substantially higher than ≈10 J cm-2 in single-crystal films with free carrier concentrations lower than ≈10 19 cm -3 . By increasing thickness, films with lower carrier densities can deliver relevant levels of sheet conductance (<200 Ω sq -1 ) while remaining transparent. These lifetime laser damage threshold measurements offer systematic criteria to select materials aimed at handling high optical powers in optoelectronics devices and emerging plasmonic and metamaterials for lasers.

36 MATERIALS SCIENCE↗
NASA NTRS1983

Transparent conductive coatings

Thin film transparent conductors are discussed. Materials with electrical conductivity and optical transparency are highly desirable in many optoelectronic applications including photovoltaics. Certain binary oxide semiconductors such as tin oxide (SnO2) and indium oxide (In2O3) offer much better performance tradeoff in optoelectronics as well as better mechanical and chemical stability than thin semitransparent films. These thin-film transparent conductors (TC) are essentially wide-bandgap degenerate semiconductors - invariably n-type - and hence are transparent to sub-bandgap (visible) radiation while affording high electrical conductivity due to the large free electron concentration. The principal performance characteristics of TC's are, of course, electrical conductivity and optical transmission. The TC's have a refractive index of around 2.0 and hence act as very efficient antireflection coatings. For using TC's in surface barrier solar cells, the photovoltaic barrier is of utmost importance and so the work function or electron affinity of the TC is also a very important material parameter. Fabrication processes are discussed.

Ashok, S.↗
NASA NTRS1994

Antenna sunshield membrane

An RF-transparent sunshield membrane covers an antenna reflector such as a parabolic dish. The blanket includes a single dielectric sheet of polyimide film 1/2-mil thick. The surface of the film facing away from the reflector is coated with a transparent electrically conductive coating such as vapor-deposited indium-tin oxide. The surface of the film facing the reflector is reinforced by an adhesively attached polyester or glass mesh, which in turn is coated with a white paint. In a particular embodiment of the invention, polyurethane paint is used. In another embodiment of the invention, a layer of paint primer is applied to the mesh under a silicone paint, and the silicone paint is cured after application for several days at room temperature to enhance adhesion to the primer.

Bogorad, Alexander↗
NASA NTRS2012

Graphene Transparent Conductive Electrodes for Next- Generation Microshutter Arrays

Graphene is a single atomic layer of graphite. It is optically transparent and has high electron mobility, and thus has great potential to make transparent conductive electrodes. This invention contributes towards the development of graphene transparent conductive electrodes for next-generation microshutter arrays. The original design for the electrodes of the next generation of microshutters uses indium-tin-oxide (ITO) as the electrode material. ITO is widely used in NASA flight missions. The optical transparency of ITO is limited, and the material is brittle. Also, ITO has been getting more expensive in recent years. The objective of the invention is to develop a graphene transparent conductive electrode that will replace ITO. An exfoliation procedure was developed to make graphene out of graphite crystals. In addition, large areas of single-layer graphene were produced using low-pressure chemical vapor deposition (LPCVD) with high optical transparency. A special graphene transport procedure was developed for transferring graphene from copper substrates to arbitrary substrates. The concept is to grow large-size graphene sheets using the LPCVD system through chemical reaction, transfer the graphene film to a substrate, dope graphene to reduce the sheet resistance, and pattern the film to the dimension of the electrodes in the microshutter array. Graphene transparent conductive electrodes are expected to have a transparency of 97.7%. This covers the electromagnetic spectrum from UV to IR. In comparison, ITO electrodes currently used in microshutter arrays have 85% transparency in mid-IR, and suffer from dramatic transparency drop at a wavelength of near-IR or shorter. Thus, graphene also has potential application as transparent conductive electrodes for Schottky photodiodes in the UV region.

Li, Mary↗
DOE OSTI2020

Combinatorial Study of MZO Emitters for CdTe-Based Solar Cells

Precise band alignment at the front interface of CdTe-based solar cells is necessary to reduce photoexcited charge carrier recombination and to enable higher energy conversion efficiencies. Magnesium zinc oxide is not only transparent but also offers the ability to tune the conduction band offset with CdTe at the front of the device stack. In this work, we describe reactive sputtering of Mg 1-x Zn x O using metal targets and its application in CdTe photovoltaics. Combinatorial libraries of Mg 1-x Zn x O were created to tune the conduction band alignment for the optimal performance of CdTe solar cells. Band gap variation of more than 0.4 eV is achieved across a 3-inch substrate. Kelvin probe measurements demonstrate variance of work function across the substrate. Device performance is optimized at band gaps of 3.5 eV for the CdTe device processing conditions employed in this study.

14 SOLAR ENERGY↗
DOE OSTI2024

A Free-Standing Boron-Doped Diamond Grid Electrode for Fundamental Spectroelectrochemistry

Spectroelectrochemistry (SEC) is a powerful technique that enables a variety of redox properties to be studied, including formal potential (E o ), thermodynamic values (ΔG, ΔH, ΔS), diffusion coefficient (D), electron transfer stoichiometry (n), and others. SEC requires an electrode which light can pass through while maintaining sufficient electrical conductivity. This has been traditionally composed of metal or metal oxide films atop transparent substrates like glass, quartz, or metallic mesh. Robust electrode materials like boron-doped diamond (BDD) could help expand the environments in which SEC can be performed, but most designs are limited to thin films (~100–200 nm) on transparent substrates less resilient than free-standing BDD. Here, this work presents a free-standing BDD grid electrode (G-BDD) for fundamental SEC measurements, using the well-characterized Fe(CN) 6 3–/4– redox couple as proof-of-concept. With a combination of cyclic voltammetry (CV), thin-layer SEC, and chronoabsorptometry, several of the redox properties mentioned above were calculated and compared. For E o' , n, and D, similar results were obtained when comparing the CV [E o' = +0.279 (±0.002) V vs Ag/AgCl; n = 0.97; D = 4.1 × 10 –6 cm 2 ·s –1 ] and SEC [E o' = +0.278 (±0.001) V vs Ag/AgCl; n = 0.91; D = 5.2 × 10 –6 cm 2 ·s –1 ] techniques. Both values align with what has been previously reported. To calculate D from the SEC data, modification of the classical equation used in chronoabsorptometry was required to accommodate the G-BDD electrode geometry. Overall, this work expands on the applicability of SEC techniques and BDD as a versatile electrode material.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Potential dependent spectroelectrochemistry of electrofluorogenic dyes on indium–tin oxide

Indium-tin oxide (ITO) is used in a variety of applications due to its electrical conductivity and optical transparency. Moreover, ITO-coated glass is a common working electrode for spectroelectrochemistry. Thus, the ITO substrates should exhibit well-understood spectroscopic characteristics. Here, we report anomalous potential-dependent luminescence emission from three structurally dissimilar electrofluorogenic probe on ITO-coated glass. The three probes, flavin mononucleotide, resorufin, and Nile blue, show the expected fluorescence modulation between their oxidized, emissive forms and their reduced, nonfluorescent forms at low laser irradiance and/or high concentrations. However, at high irradiance and/or low concentration, the emission intensity increases at reducing potentials, contrary to expectations. In addition, a strong interplay between probe molecule concentration and laser irradiance is observed. We attribute the anomalous behavior to a combination of (1) irradiance-dependent ITO carrier dynamics, and (2) interaction of the fluorescent probe with ITO at reducing potentials resulting in a charge transfer state with altered emission behavior. Thus, the potential- and irradiance-dependent behavior of ITO and the resulting charge transfer state may not only interfere with the observation of potential-dependent fluorescence from redox probes but can completely reverse the polarity of the potential-dependent luminescence, especially at high irradiance and low concentration.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Mg x Zn 1−x O contact to CuGa 3 Se 5 absorber for photovoltaic and photoelectrochemical devices

Abstract CuGa 3 Se 5 is a promising candidate material with wide band gap for top cells in tandem photovoltaic and photoelectrochemical (PEC) devices. However, traditional CdS contact layers used with other chalcopyrite absorbers are not suitable for CuGa 3 Se 5 due to the higher position of its conduction band (CB) minimum. Mg x Zn 1− x O (MZO) is a transparent oxide with adjustable band gap and CB position as a function of magnesium composition, but its direct application is hindered by CuGa 3 Se 5 surface oxidation. Here, MZO is investigated as a contact (n-type ‘buffer’ or ‘window’) material to CuGa 3 Se 5 absorbers pretreated in Cd 2+ solution, and an onset potential close to 1 V vs reversible hydrogen electrode in 10 mM hexaammineruthenium (III) chloride electrolyte is demonstrated. The Cd 2+ surface treatment changes the chemical composition and electronic structure of the CuGa 3 Se 5 surface, as demonstrated by photoelectron spectroscopy measurements. The performance of CuGa 3 Se 5 absorber with Cd 2+ treated surface in the solid-state test structure depends on the Zn/Mg ratio in the MZO layer. The measured open circuit voltage of 925 mV is promising for tandem PEC water splitting with CuGa 3 Se 5 /MZO top cells.

36 MATERIALS SCIENCE↗
NASA NTRS1997

Space Environment Stability and Physical Properties of New Materials for Space Power and Commercial Applications

Useful and informative results were obtained on virtually all materials investigated. For example, the stability of ITO-based arc-proof transparent coatings was greatly improved by substitution of silicon oxide for magnesium fluoride as a dopant. Research on 'air-doped' ITO films has yielded new insight into their conduction mechanism which will help in further development of these coatings. Some air-doped films were found to be extremely pressure sensitive. This work may lead to improved, low-cost gas sensors and vacuum gauges. Work on another promising transparent arc-proof coating (titanium oxide) was initiated in collaboration with industry. Graphite oxide-like materials were synthesized and tested for possible use in high energy-density batteries and other applications. We also started a high-priority project to find the cause of unexpected environmental damage to the exterior of the Hubble Space Telescope (HST) discovered on a recent Shuttle mission. Materials were characterized before and after exposure to soft x-rays and other threats in ground-based simulators.

Hambourger, Paul D.↗
NASA NTRS1985

GaAs Schottky barrier photo-responsive device and method of fabrication

A gallium arsenide photo-responsive device is provided with an intermediate, transparent layer of a refractory metal or alkaline earth metal forming a tenacious bond between a non-hydroscopic oxide layer and a noble metal Schottky barrier layer. The device has a gallium arsenide substrate with a predetermined type conductivity and a gallium arsenide epitaxial layer with the same type conductivity but a lower charge carrier concentration grown on the substrate. The oxide layer is formed to cover the epitaxial layer, and the transparent metal layer followed by the noble metal layer are deposited upon the oxide layer. An interdigitated ohmic contact is then formed upon the noble metal layer.

Alcorn, G. E.↗
DOE OSTI2020

Boron phosphide as a p-type transparent conductor: Optical absorption and transport through electron-phonon coupling

Boron phosphide has recently been identified as a potential high-hole-mobility transparent conducting material. This promise arises from its low hole effective masses. However, boron phosphide has a relatively small, 2 eV, indirect bandgap which will affect its transparency. In this study, we computationally study both optical absorption across the indirect gap and phonon-limited electronic transport to quantify the potential of boron phosphide as a p-type transparent conductor. We find that phonon-mediated indirect optical absorption is weak in the visible spectrum and that the phonon-limited hole mobility is very high (around 900 cm 2 /Vs) at room temperature. This exceptional mobility comes from the combination of a low hole effective mass and very weak scattering by polar phonon modes. We rationalize the weak scattering by the less ionic bonding in boron phosphide compared to oxides. We suggest that this could be a general advantage of nonoxides for p-type transparent conducting applications. Using our computed properties, we assess the transparent conductor figure of merit of boron phosphide and show that it exceeds by one order of magnitude that of established p-type transparent conductors, confirming the potential of this material.

36 MATERIALS SCIENCE↗
NASA NTRS2013

Ceramic Composite Thin Films

A ceramic composite thin film or layer includes individual graphene oxide and/or electrically conductive graphene sheets dispersed in a ceramic (e.g. silica) matrix. The thin film or layer can be electrically conductive film or layer depending the amount of graphene sheets present. The composite films or layers are transparent, chemically inert and compatible with both glass and hydrophilic SiOx/silicon substrates. The composite film or layer can be produced by making a suspension of graphene oxide sheet fragments, introducing a silica-precursor or silica to the suspension to form a sol, depositing the sol on a substrate as thin film or layer, at least partially reducing the graphene oxide sheets to conductive graphene sheets, and thermally consolidating the thin film or layer to form a silica matrix in which the graphene oxide and/or graphene sheets are dispersed.

Ruoff, Rodney S.↗
DOE OSTI2023

Layered metals as polarized transparent conductors

The quest to improve transparent conductors balances two key goals: increasing electrical conductivity and increasing optical transparency. To improve both simultaneously is hindered by the physical limitation that good metals with high electrical conductivity have large carrier densities that push the plasma edge into the ultra-violet range. Technological solutions reflect this trade-off, achieving the desired transparencies only by reducing the conductor thickness or carrier density at the expense of a lower conductance. Here we demonstrate that highly anisotropic crystalline conductors offer an alternative solution, avoiding this compromise by separating the directions of conduction and transmission. We demonstrate that slabs of the layered oxides Sr 2 RuO 4 and Tl 2 Ba 2 CuO 6+δ are optically transparent even at macroscopic thicknesses >2 μm for c-axis polarized light. Underlying this observation is the fabrication of out-of-plane slabs by focused ion beam milling. This work provides a glimpse into future technologies, such as highly polarized and addressable optical screens.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Chalcogenide Perovskite YScS 3 as a Potential p-Type Transparent Conducting Material

Transparent conducting materials (TCMs) have been widely used in optoelectronic applications such as touchscreens, flat panel displays and thin film solar cells. These applications of TCMs are currently dominated by n-type doped oxides. High-performance p-type TCMs are still lacking due to their low hole mobility or p-type doping bottleneck, which impedes efficient device design and novel applications such as transparent electronics. Here, based on first-principles calculations, we propose chalcogenide perovskite YScS 3 as a promising p-type TCM. According to our calculations, its optical absorption onset is above 3 eV, which allows transparency to visible light. Its hole conductivity effective mass is 0.48m 0 , which is among the smallest in p-type TCMs, suggesting enhanced hole mobility. It could be doped to p-type by group-II elements on cation sites, all of which yield shallow acceptors. Here, combining these properties, YScS 3 holds great promise to enhancing the performance of p-type TCMs toward their n-type counterparts.

36 MATERIALS SCIENCE↗
DOE OSTI2024

“Green” Fabrication of High-performance Transparent Conducting Electrodes by Blade Coating and Photonic Curing on PET for Perovskite Solar Cells

This study presents an innovative material processing approach to fabricate transparent conducting electrodes (TCEs) on polyethylene terephthalate (PET) substrates using blade coating and photonic curing. The hybrid TCEs consist of a multiscale Ag network, combining silver metal bus lines and nanowires, overcoated by an indium zinc oxide layer, and then photonically cured. Blade coating ensures film uniformity and thickness control over large areas. Photonic curing, a non-thermal processing method with significantly lower carbon emissions, enhances the conductivity and transparency of the coated layers. Our hybrid TCEs achieve an average transmittance of (81 ± 0.4)% referenced to air ((90 ± 0.4)% referenced to the PET substrate) in the visible range, an average sheet resistance of (11 ± 0.5) Ω sq−1, and an average surface roughness of (4.3 ± 0.4) nm. We benchmark these values against commercial PET/TCE substrates. Mechanical durability tests demonstrate <3% change in resistance after 2000 bending cycles at a 1 in radius. The scalable potential of the hybrid TCE fabrication method is demonstrated by high uniformity and excellent properties in 7 in × 8 in large-area samples and by performing the photonic curing process at 11 m min−1. Furthermore, halide perovskite solar cells fabricated on these hybrid TCEs achieve average and champion power conversion efficiencies of (10.5 ± 1.0) % and 12.2%, respectively, and significantly outperform devices made on commercial PET/TCEs. This work showcases our approach as a viable pathway for high-speed “green” manufacturing of high-performance TCEs on PET substrates for flexible optoelectronic devices.

Bonner, Justin C↗
DOE OSTI2019

Solution-Processed Composite Transparent Metal Network Conductors for Next Generation Scalable PV

Transparent conductors (TCs) are essential components of thin film PV cells. Inherently, ITO and other related TC oxides, have fundamental trade-offs that balance conductivity versus optical transmission losses from metallic absorption and reflectivity. Furthermore, the ITO sputtering, materials and patterning costs represent one of the highest cost elements in the thin film cell process. As we consider emerging technologies such as roll to roll processing on lower temperature substrates, the problem is compounded by high ITO processing temperatures. Low temperature alternatives do exist, however, they cannot reach the metrics for high efficiency PV on their own. Numerical modeling has shown that combining high transparency, modestly conducting films with printed conductive grids can provide a TC with a 30% reduction in power loss relative to ITO. During this talk, current work on nanowire and printed TC films will be presented and the scale-up pathways for these technologies will be discussed.

14 SOLAR ENERGY↗