Search NASA⌕ Search

SEARCH · Search NASA

Results for “transparent conducting oxide”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Broad Frequency Shift of Parametric Processes in Epsilon-Near-Zero Time-Varying Media

The ultrafast changes of material properties induced by short laser pulses can lead to a frequency shift of reflected and transmitted radiation. Recent reports highlight how such a frequency shift is enhanced in spectral regions where the material features a near-zero real part of the permittivity. Here, we investigate the frequency shift for fields generated by four-wave mixing. In our experiment, we observed a frequency shift of more than 60 nm (compared to the pulse width of ~40 nm) in the phase conjugated radiation generated by a 500 nm aluminium-doped zinc oxide (AZO) film pumped close to the epsilon-near-zero wavelength. Our results indicate applications of time-varying media for nonlinear optics and frequency conversion.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Solution-Processed Oxide Thin Films for Perovskite Photovoltaics (Final Report)

The overarching goal of the voucher project is to evaluate the suitability of NexTC materials as functional layers in perovskite photovoltaic technology. There are several different perovskite device configurations that are being pursued for commercialization. Most are superstrate configuration (light enters the device through the glass substrate) and can be subdivided into two categories: PIN and NIP. At minimum, PIN devices have a transparent conductor (typically Indium Tin Dioxide [ITO] or Fluorine-Doped Tin Oxide [FTO]) and hole transport layer (HTL) deposited on glass before the perovskite is deposited. Alternatively, NIP devices have a transparent conductor and electron transport layer (ETL) deposited before the perovskite is deposited. NexTC produces several inks that can be deposited to replace or modify the transparent conductor and/or the ETL or HTL, depending on the device. NLR will produce PIN and NIP perovskite devices on substrates that have been coated by NexTC and compare to NLR-standard devices that perform among the best for research labs across the world. The work will ultimately expose NexTC products to the up-and-coming perovskite PV industry.

14 SOLAR ENERGY↗
DOE OSTI2021

Polarization Selectivity of Aloof-Beam Electron Energy-Loss Spectroscopy in One-Dimensional ZnO Nanorods

Orientation-dependent electronic properties of wurtzite zinc oxide nanorods are characterized by aloof-beam electron energy-loss spectroscopy (EELS) carried out in a scanning transmission electron microscope (STEM). The two key crystal orientation differentiating transitions specific to the in-plane (13.0 eV) and out-of-plane (11.2 eV) directions with respect to the wurtzite structure are examined by first-principles density-functional theory calculations. We note some degree of orientation dependence at the onset of direct band gap transition near 3.4 eV. We demonstrate that good polarization selectivity can be achieved by placing the electron probe at different locations around the specimen with increasing impact parameter while keeping the beam-specimen orientation fixed. The observed results are qualitatively elucidated in terms of the perpendicular electric fields generated by the fast electron (60 kV) used in the microscope. The fact that good polarization selectivity can be achieved by aloof-beam EELS without the requirement of sample reorientation is an attractive aspect from the characterization method point of view in the STEM-EELS community.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Structure-property relationships and mobility optimization in sputtered La-doped BaSn O 3 films: Toward 100cm 2 V -1 s -1

he wide band gap semiconducting perovskite BaSnO 3 is of high current interest due to outstanding room temperature mobility at high electron density, fueled by potential applications in oxide, transparent, and power electronics. Due in part to a lack of lattice-matched substrates, BaSnO 3 thin films suffer from high defect densities, however, limiting electron mobility. Additionally, the vast majority of BaSnO 3 thin film research has focused on pulsed laser deposition or molecular beam epitaxy. In this work, we present an exhaustive optimization of the mobility of Ba 0.98 La 0.02 SnO 3 films grown by a scalable, high-throughput method: high-pressure-oxygen sputter deposition. Considering target synthesis conditions, substrate selection, buffer layer structure, deposition temperature, deposition rate, thickness, and postdeposition annealing conditions, and by combining high-resolution x-ray diffraction, reciprocal space mapping, rocking curve analysis, scanning transmission electron microscopy, atomic force microscopy, and temperature-dependent electronic transport measurements, detailed understanding of synthesis-structure-property relationships is attained. Optimized room temperature mobility of 96 cm 2 V –1 s –1 is achieved in vacuum-annealed GdScO 3 (110)/BaSnO 3 (120 nm)/Ba 0.98 La 0.02 SnO 3 (200 nm) heterostructures, as well as 92 cm 2 V –1 s –1 on unbuffered substrates and 87 2 V –1 s –1 without postdeposition annealing. These results, including important trends in defect densities and a surprising dependence of mobility on lattice mismatch, substantially expand the understanding of the interplay between deposition conditions, microstructure, and transport in doped BaSnO 3 films, establishing competitive mobilities in films fabricated via a scalable, high-throughput, industry-standard technique.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Sputtered indium tin oxide as a recombination layer formed on the tunnel oxide/poly-Si passivating contact enabling the potential of efficient monolithic perovskite/Si tandem solar cells

We focus on utilizing sputtered indium tin oxide (ITO) as a recombination layer, having low junction damage to an n-type silicon solar cell with a front-side tunnel oxide passivating electron contact, thereby enabling the development of a high efficiency monolithic perovskite/Si tandem device. High transparency and low resistivity ITO films are deposited via low power DC magnetron sputtering at room temperature onto a front-side thin SiO x /n + poly-Si contact in a complete Cz n-Si cell with a back-side Al 2 O 3 /SiN x passivating boron-diffused p + -emitter on a random pyramid textured surface. We report the cell characteristics before and after ITO sputtering, and we find a cure at 250 °C in air is highly effective at mitigating any sputtering induced damage. Our ITO coated sample resulted in an implied open-circuit voltage (iV oc ) of 684.7 ± 11.3 mV with the total saturation current density of 49.2 ± 14.8 fA/cm 2 , an implied fill factor (iFF) of 81.9 ± 0.8%, and a contact resistivity in the range of 60 mΩ-cm 2 to 90 mΩ-cm 2 . After formation of a local Ag contact to the rear emitter and sputtered ITO film as the front-side contact without grid fingers, the pseudo-efficiency of 20.2 ± 0.5% was obtained with the V oc of 670.4 ± 7 mV and pseudo FF of 77.3 ± 1.3% under simulated one sun with the calculated short-circuit current density of 30.9 mA/cm 2 from the measured external quantum efficiency. Furthermore, our modelling result shows that efficiency exceeding 25% under one sun is practically achievable in perovskite/Si tandem configuration using the ITO recombination layer connecting a perovskite top cell and a poly-Si bottom cell.

14 SOLAR ENERGY↗
DOE OSTI2023

Migration of Ga vacancies and interstitials in β – Ga 2 O 3

Pathways and energy barriers for the migration of Ga vacancies (V Ga ) and Ga interstitials (Ga i ) in β–Ga 2 O 3 are explored using hybrid functional calculations and the nudged elastic band method. Considering β–Ga 2 O 3 as primarily being an n-type semiconductor, we focus on defect charge states relevant under such conditions: $V^{3 –}_{Ga}$, Ga$^{3+}_{i}$, and Ga$^{+}_{i}$. Notably, we describe a mechanism by which V Ga can transform between its different split configurations. In all cases, the intermediate state consists of a vacancy split between three Ga sites—a three-split vacancy—which enables passage over a significantly lower energy barrier. This is because it avoids the unfavorable simple vacancy at the tetrahedral Ga site. The proposed mechanism lowers the overall barrier for $V^{3–}_{Ga}$ diffusion along the [001] crystal direction from 1.73 to 0.97 eV, whereas the 2.08 eV barrier for the [100] and [010] directions is unaffected. For Ga$^{3+}_{i}$, we obtain similar overall migration barriers of 0.72, 0.80, and 1.02 eV for the [010], [001], and [100] directions, respectively. Ga$^{+}_{i}$ exhibits a strong preference for diffusion within the large eight-sided channel; the overall migration barrier is 0.92 eV for the [010] direction, and 2.16 eV for the [001] and [100] directions. The limiting step for the two latter directions involves ionization of Ga$^{+}_{i}$ followed by a jump to an adjacent large eight-sided channel as Ga$^{3+}_{i}$. Finally, our results are discussed in light of experimental observations of thermally activated recovery processes in irradiated material.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Multistability of isolated and hydrogenated Ga–O divacancies in β–Ga 2 O 3

This work systematically explores 19 unique configurations of the close-associate Ga–O divacancies (V Ga V O ) in β–Ga 2 O 3 , including their complexes with H impurities, using hybrid functional calculations. Interestingly, most configurations are found to retain the negative-U behavior of V O , as they exhibit a thermodynamic (–/3–) charge-state transition level energetically located in the upper part of the band gap, where the 3– charge state is associated with the formation of a Ga–Ga dimer. The energy positions of the thermodynamic (–/3–) charge-state transition levels divide the divacancy configurations into three different groups, which can be understood from the three possible Ga–Ga dimerizations resulting from the tetrahedral and octahedral Ga sites. The relative formation energies of the different divacancy configurations, and hence the electrical activity of the divacancies, is found to depend on the Fermi-level position, and the energy barriers for transformation between different divacancy configurations are explored from nudged elastic band calculations. Hydrogenation of the divacancies is found to either passivate their negative-U charge-state transition levels or shift them down in Fermi level position, depending on whether the H resides at V O or forms an O–H bond at V Ga , respectively. Finally, the divacancy is discussed as a potential origin of the so-called E$^{*}_{2}$ center previously observed by deep-level transient spectroscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Unraveling the transformation pathway of the 𝛽 to 𝛾 phase transition in Ga 2 ⁢O 3 from atomistic simulations

Defect spinel 𝛾−Ga 2 ⁢O 3 is the least stable polymorph of Ga 2 ⁢O 3 , so its frequent appearance as a structural defect within or on the surface of monoclinic 𝛽−Ga 2 ⁢O 3 remains a mystery. Through first-principles calculations, we explore potential pathways for the phase transition from 𝛽−Ga 2⁢ O 3 to 𝛾−Ga 2 ⁢O 3 , and examine two key driving forces: tensile strain and Ga deficiency. When configurational entropy contributions to phase energies are included, the 𝛾 phase becomes energetically competitive with the 𝛽 phase, with the free energy difference between these phases diminishing even further under Ga-deficient conditions. Notably, a stability crossover occurs at room temperature at high vacancy concentrations ([V$^{3−}_{Ga}$]>3%) . A simple model 𝛽 → 𝛾 transformation pathway is identified, comprising two primary reactions, that enables the formation of the 𝛾 phase via simultaneous migration of Ga atoms from tetrahedral lattice sites to octahedral interstitial positions. The transformation barriers are prohibitively large in pristine Ga 2 ⁢O 3 , but can be substantially reduced by: (1) the presence of Ga vacancies, (2) elongational strains along the crystallographic 𝑎-axis, and (3) when volumetric relaxations are possible during transformation. These results elucidate prior experimental observations, where 𝛾−Ga 2⁢ O 3 is seen on damaged surfaces or in highly 𝑛-type 𝛽−Ga 2⁢ O 3 environments, which support Ga deficiency and mechanical strain. The insights into the driving forces and mechanisms of 𝛾−Ga 2⁢ O 3 formation enhance understanding of how localized strain and nonequilibrium defect concentrations may facilitate its formation from the 𝛽 phase.

Defects↗
DOE OSTI2024

From Design to Device: Challenges and Opportunities in Computational Discovery of p -Type Transparent Conductors

A high-performance p -type transparent conductor (TC) does not yet exist but could lead to advances in a wide range of optoelectronic applications and enable new architectures for, e.g., next-generation photovoltaic (PV) devices. High-throughput computational material screenings have been a promising approach to filter databases and identify new p -type TC candidates and some of these predictions have been experimentally validated. However, most of these predicted candidates do not have experimentally achieved properties on par with n -type TCs used in solar cells and therefore have not yet been used in commercial devices. Thus, there is still a significant divide between transforming predictions into results that are actually achievable in the laboratory and an even greater lag in scaling predicted materials into functional devices. In this perspective, we outline some of the major disconnects in this materials discovery process—from scaling computational predictions into synthesizable crystals and thin films in the laboratory to scaling laboratory-grown films into real-world solar devices—and share insights to inform future strategies for TC discovery and design. Published by the American Physical Society 2024

14 SOLAR ENERGY↗
DOE OSTI2022

A new route to obtain fluorescence X-ray absorption spectra of compounds and to remove the self-absorption induced nonlinearity in the spectra

A new route to obtain fluorescence X-ray absorption spectra of compounds and to remove the self-absorption induced nonlinearity in the spectra is described. The fluorescent intensity If is linearly proportional to the absorption coefficient μ. For studies of surface structures around an element (κ) the fluorescence detection is often the mode of choice. However, the measurement may suffer from a self-absorption (SA) effect which nonlinearly distorts the spectra. The effect is severe when κ is concentrated or the measurements are carried out in certain geometries. Here, the correlations among emission events in compounds are examined following resonance X-ray core-electron excitation within κ. Under conditions leading to SA, If emitted from κ apparently has a conjugated relationship with the fluorescent intensities simultaneously emitted from other elements (ξ). Normalizing the former (κ) by the latter (ξ) will largely remove SA effects and reduce this nonlinear problem to a tractable linear problem. This does result in a moderate reduction of the spectral amplitude due to the so-called secondary emission from ξ excited by the emission from κ. Nonetheless, the resulting spectra will allow one to accurately determine bond distances and disorder and, in some respects, can be superior to spectra obtained via the absorption channel. For μξ < μκ and grazing incidence geometry, the amplitude reduction can be small and simple normalization is sufficient to restore the spectral integrity with remarkable accuracy. This has been instrumental in unravelling the surface and subsurface structures around cations in amorphous Ga–In–O and Zn–Sn–O films which are otherwise inaccessible due to severe SA effects. This method has also been applied to several samples with μξ ≃ μκ to examine its applicability. For these samples, the amplitude reduction is 12 ± 4% versus their standards for the data measured with the classical 45°/45° geometry. This experimental method is easy to implement. Since If from κ and ξ are measured by the same detector system, it is also superior to other methods in removing systematic errors such as detector system nonlinearity, electronic noise, and some beam instabilities, and in removing spectral imperfections due to, for example, SA effects, diffraction effects and sample inhomogeneity. The distortions resulting from the latter can be severe in the spectra measured in transmission mode.

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

Perspectives of Open-Air Processing to Enable Perovskite Solar Cell Manufacturing

We report high throughput open-air processing techniques for the scalable production of all device and barrier layers for perovskite photovoltaics (PV). This work discusses and resolves some of the most formidable barriers to module-level scaling that the perovskite community has been facing. Our advanced technoeconomic manufacturing analysis indicates that vacuum-based processes with high capital expenditures (CapEx) and low throughputs dominate the cost of production. Open-air fabrication methods offer low CapEx routes to manufacturing, but achieving reproducibility in ambient conditions with varying relative humidity has been a persistent challenge. The use of rapid processing methods with plasma curing to convert films from the solution-state enables reproducibility, moisture immunity, and the highest perovskite PV efficiency produced in open-air. These methods are readily translatable to in-line processing where layers are sequentially deposited without the need for lengthy post-annealing steps that reduce throughput and involve additional equipment. Significant progress is demonstrated in reduced manufacturing costs as perovskites contend as a commercially viable next-generation thin film PV technology.

14 SOLAR ENERGY↗
DOE OSTI2020

Dynamical Control of Broadband Coherent Absorption in ENZ Films

Interferometric effects between two counter-propagating beams incident on an optical system can lead to a coherent modulation of the absorption of the total electromagnetic radiation with 100% efficiency even in deeply subwavelength structures. Coherent perfect absorption (CPA) rises from a resonant solution of the scattering matrix and often requires engineered optical properties. For instance, thin film CPA benefits from complex nanostructures with suitable resonance, albeit at a loss of operational bandwidth. In this work, we theoretically and experimentally demonstrate a broadband CPA based on light-with-light modulation in epsilon-near-zero (ENZ) subwavelength films. We show that unpatterned ENZ films with different thicknesses exhibit broadband CPA with a near-unity maximum value located at the ENZ wavelength. By using Kerr optical nonlinearities, we dynamically tune the visibility and peak wavelength of the total energy modulation. Our results based on homogeneous thick ENZ media open a route towards on-chip devices that require efficient light absorption and dynamical tunability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1984

Highly photoconducting O2-doped CdS films deposited by spray pyrolysis

CdS films have been prepared by spraying in air solutions of thiourea with either cadmium chloride or cadmium acetate with varying mole ratio and substrate temperature, and subsequently heat treating in oxygen. Substrates included both bare glass or sapphire and transparent conducting oxide-coated sapphire for electrical measurements lateral and transverse to the CdS plane, respectively. Dark resistances of over 10 to the 14th ohms and light-to-dark conductivities of up to 10 to the 7th were obtained using uncoated substrates. The use of Cd(C2H3O2)2 in place of CdCl2 greatly increased the speed of response although with some sacrifice in photoconductivity. Deposition of CdS on ITO-coated surfaces led to greatly reduced dark resistances for the case of CdCl2, but not Cd(C2H3O2)2, presumably due to HCl reaction with the ITO coating in the course of spraying with the former. Ion microprobe analysis detected indium within the CdS films exhibiting low dark resistance. Measurements of the dark and light conductivities at temperatures down to 77 K are given as are the response times for unetched and HCl-etched surfaces.

Richards, D.↗
NASA NTRS1978

Solar cells having integral collector grids

A heterojunction or Schottky barrier photovoltaic device is described, comprising a conductive base metal layer. A back surface field region was formed at the interface between the device and the base metal layer, a transparent, conductive mixed metal oxide layer in integral contact with the n-type layer of the heterojunction or Schottky barrier device. A metal alloy grid network was included. An insulating layer prevented electrical contact between the conductive metal base layer and the transparent, conductive metal oxide layer.

Evans, J. C., Jr.↗
DOE OSTI2020

Enabling Efficiencies > 22.5% with Metal Oxide Passivating Contacts using Low-Cost Spatial Atomic Layer Deposition (Final Technical Report)

In this project, the University of Central Florida (UCF) worked to both increase module efficiency and reduce manufacturing cost by driving demonstrated lab-scale passivating contact technology using materials and processes compatible with high-volume manufacturing for crystalline silicon (c-Si) photovoltaic (PV) cells. Passivating contacts have garnered significant attention in recent years. They provide a means of suppressing contact recombination, a loss mechanism that limits the performance of industrially relevant cell architectures like Al back surface field (Al-BSF) cells and passivated emitter and rear cells (PERC). Most of the development of passivating contact technology has focused on the use of doped amorphous silicon or doped polysilicon contacts, but both suffer from parasitic optical absorption amongst other issues. Our team developed fully transparent hole-selective heterojunctions, deposited using atomic layer deposition (ALD), and showed how they could be incorporated into c-Si PV cells. The team conducted experiments to understand the process-structure-property relationship of hole-selective oxides, surface passivation oxide materials, and transparent conductive oxides deposited by ALD, and use that understanding to reduce contact recombination, contact resistivity, and parasitic optical absorption within c-Si PV cells. Before getting into the details of the report, we would like to note that COVID-19 has made it more challenging to conduct experimental research at UCF. UCF has a number of mandatory policies in place to ensure social distancing, testing, and contact tracing are all carried out in day-to-day operations. Despite these challenges, we worked diligently to make progress on this project in a manner that was as safe as possible. Over the course of the project, the UCF team and its collaborators have made the following discoveries and developments.

14 SOLAR ENERGY↗
NASA NTRS2006

Electrically Conductive Anodized Aluminum Surfaces

Anodized aluminum components can be treated to make them sufficiently electrically conductive to suppress discharges of static electricity. The treatment was conceived as a means of preventing static electric discharges on exterior satin-anodized aluminum (SAA) surfaces of spacecraft without adversely affecting the thermal-control/optical properties of the SAA and without need to apply electrically conductive paints, which eventually peel off in the harsh environment of outer space. The treatment can also be used to impart electrical conductivity to anodized housings of computers, medical electronic instruments, telephoneexchange equipment, and other terrestrial electronic equipment vulnerable to electrostatic discharge. The electrical resistivity of a typical anodized aluminum surface layer lies between 10(exp 11) and 10(exp 13) Omega-cm. To suppress electrostatic discharge, it is necessary to reduce the electrical resistivity significantly - preferably to < or = 10(exp 9) Omega-cm. The present treatment does this. The treatment is a direct electrodeposition process in which the outer anodized surface becomes covered and the pores in the surface filled with a transparent, electrically conductive metal oxide nanocomposite. Filling the pores with the nanocomposite reduces the transverse electrical resistivity and, in the original intended outer-space application, the exterior covering portion of the nanocomposite would afford the requisite electrical contact with the outer-space plasma. The electrical resistivity of the nanocomposite can be tailored to a value between 10(exp 7) and 10(exp 12) Omega-cm. Unlike electrically conductive paint, the nanocomposite becomes an integral part of the anodized aluminum substrate, without need for adhesive bonding material and without risk of subsequent peeling. The electrodeposition process is compatible with commercial anodizing production lines. At present, the electronics industry uses expensive, exotic, electrostaticdischarge- suppressing finishes: examples include silver impregnated anodized, black electroless nickel, black chrome, and black copper. In comparison with these competing finishes, the present nanocomposite finishes are expected to cost 50 to 20 percent less and to last longer.

Nguyen, Trung Hung↗
DOE OSTI2025

Elucidating the Role of Hydrogen at c‐In 2 O 3 /a‐In 2 O 3− x Interface

Ab initio molecular dynamics simulations and hybrid functional electronic structure calculations are employed to determine the formation, the structural and electronic properties, and the dynamics of covalent (In—OH) and ionic (In—H—In) hydrogen defects at crystalline-In 2 O 3 /amorphous-In 2 O 3−x interface. This comprehensive computational study considers (i) various interstitial and substitutional hydrogen site locations within the crystalline, amorphous, and interfacial regions; (ii) several oxygen-to-hydrogen ratios; and (iii) possible defect charged states. The results reveal hydrogen's inability to fully passivate the undercoordinated under-shared in atoms in amorphous highly substoichiometric oxide, giving rise to the formation of deep electron traps even in net-charge neutral structures. These trap defects are found to be sensitive to photoexcitation, in contrast to In—OH with H's electronic states located below the valence band and to In—H—In, where H is found to maintain its charge state upon illumination. Nevertheless, H plays a critical role in photoinduced conductivity and its relaxation by promoting In—O coordination transformations at the interfacial region, including deterioration of the crystalline layer. Finally, the results help identify mobile H species and metastable H defect complexes (such as In—H—H—In, In—OH–H—In, and In—OH–O—In) that are responsible for long relaxation times of the conductivity decay.

H defects↗