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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Investigation of the Selectivity of Carrier Transport Layers in Wide-Bandgap Perovskite Solar Cells

Excellent contact passivation and selectivity are prerequisites to realize the full potential of high-material-quality perovskite solar cells, first to maximize the internal voltage (or quasi-Fermi-level separation) iV within the absorber, then to translate this high internal voltage into a high external voltage V. Experimental quantification of contact passivation and selectivity is, thus, key to improving device performance. Here, open-circuit measurements of iV oc and V oc , combined with surface photovoltage measurements, are used to systematically quantify the passivation—using iVoc as a metric—and the selectivity—defined as Soc=V oc /iV oc —of a range of common carrier transport layers to wide-bandgap (1.67 eV) perovskite absorbers. The resulting solar cells suffer from large voltage deficits, particularly when NiO x is used as the hole transport layer, even though it provides better passivation than its polymer-based counterparts (PTAA and PTAA/PFN). This indicates a poor selectivity of NiO x (Soc<0.81 for NiO x -based devices), whereas devices using polymer-based hole transport layers exhibit high selectivity (S oc =0.94–0.95). In agreement with recent reports, this low selectivity is attributed to the formation of an interlayer of non-perovskite material with high resistance to holes at the perovskite/NiO x interface. These measurements also imply that the selectivity of the C60-based electron transport layers is relatively good.

carrier transport layers↗
DOE OSTI2022

Effects of potassium treatment on SnO 2 electron transport layers for improvements of perovskite solar cells

SnO 2 has been studied intensively as an electron transport layer (ETL) for highly efficient metal halide perovskite solar cells. However, SnO 2 ETL frequently exhibits defect-related issues associated with the bulk SnO 2 and the perovskite/SnO 2 interface, and to passivate the defect states potassium ion has been used. In order to investigate the passivation effect of potassium ion, we carried out KCl treatment on the solution-processed SnO 2 ETL. It was found that KCl-treatment shifted up conduction band maximum and Fermi energy of SnO 2 , and reduced the band gap of perovskite absorber by K + diffusion, which resulted in a better conduction band alignment at perovskite/SnO 2 . Admittance spectroscopy revealed that diffused K + ions can passivate defects of the perovskite absorber layer. With the improvement of band alignment and defect passivation via the KCl treatment, the J-V hysteresis was almost eliminated and power conversion efficiency was much enhanced with improved open-circuit voltage and fill factor.

14 SOLAR ENERGY↗
NASA NTRS1993

A layered approach to structural control system design for the JPL phase B testbed

This paper describes our efforts in structural control experiments for a flexible precision structure using both passive and active control. Specifically, a layered structural control approach utilizing passive viscous dampers, colocated and noncolocated active control is used. The passive dampers and active colocated control loops are used to enhance stability and robustness and the noncolocated multivariable controller is designed with respect to a partially controlled structure to further improve the performance. Our approach to the multivariable design problem requires not only a state space model description of the plant, but also an accompanying uncertainty model. To support the multivariable robust control design development, a significant effort in system identification was undertaken. The process of identification and identified results are discussed. Noncolocated controllers are designed using the H(infinity)/mu-synthesis methodology. The order of the controller is typically large, hence, model reduction is performed for practical digital implementation on a real-time control system developed at JPL. Finally, experimental results are presented and some of lessons are discussed.

Chu, Cheng-Chih↗
NASA NTRS1985

Control plate for shock-boundary layer interaction

Paper describes tests and computations for a relatively unique technique to greatly reduce/eliminate the separation region for shock-boundary layer interactions. A number of studies have shown that the usual effects of such interactions include increased local heating and wall pressures, thickening of the boundary layer and a decrease in the momentum of the flow and, for stronger waves, flow separation. This flow situation is particularly prevalent in supersonic and hypersonic inlets where severe performance degradation can occur due to flow separation. High performance engine design generally requires a uniform entering flow field with little stagnation pressure loss. Previous approaches to the problem involved primarily active devices (e.g., suction or blowing); the present paper considers a passive device. The boundary layer separation control technique considered herein involves the placement of an embedded plate in the outer portion of the boundary layer and parallel to the wall. This control plate is situated such that the incident shock impinges upon and reflects from its surface, thus greatly lessening the pressure gradient in the low momentum near wall region.

Goodman, W. L.↗
NASA NTRS1988

Use of passive scalar tagging for the study of coherent structures in the plane mixing layer

Data obtained from the numerical simulation of a 2-D mixing layer were used to study the feasibility of using the instantaneous concentration of a passive scalar for detecting the typical coherent structures in the flow. The study showed that this technique works quite satisfactorily and yields results similar to those that can be obtained by using the instantaneous vorticity for structure detection. Using the coherent events educed by the scalar conditioning technique, the contribution of the coherent events to the total turbulent momentum and scalar transport was estimated. It is found that the contribution from the typical coherent events is of the same order as that of the time-mean value. However, the individual contributions become very large during the pairing of these structures. The increase is particularly spectacular in the case of the Reynolds shear stress.

Ramaprian, B. R.↗
NASA NTRS2007

Cooling Technology for Large Space Telescopes

NASA's New Millennium Program funded an effort to develop a system cooling technology, which is applicable to all future infrared, sub-millimeter and millimeter cryogenic space telescopes. In particular, this technology is necessary for the proposed large space telescope Single Aperture Far-Infrared Telescope (SAFIR) mission. This technology will also enhance the performance and lower the risk and cost for other cryogenic missions. The new paradigm for cooling to low temperatures will involve passive cooling using lightweight deployable membranes that serve both as sunshields and V-groove radiators, in combination with active cooling using mechanical coolers operating down to 4 K. The Cooling Technology for Large Space Telescopes (LST) mission planned to develop and demonstrate a multi-layered sunshield, which is actively cooled by a multi-stage mechanical cryocooler, and further the models and analyses critical to scaling to future missions. The outer four layers of the sunshield cool passively by radiation, while the innermost layer is actively cooled to enable the sunshield to decrease the incident solar irradiance by a factor of more than one million. The cryocooler cools the inner layer of the sunshield to 20 K, and provides cooling to 6 K at a telescope mounting plate. The technology readiness level (TRL) of 7 will be achieved by the active cooling technology following the technology validation flight in Low Earth Orbit. In accordance with the New Millennium charter, tests and modeling are tightly integrated to advance the technology and the flight design for "ST-class" missions. Commercial off-the-shelf engineering analysis products are used to develop validated modeling capabilities to allow the techniques and results from LST to apply to a wide variety of future missions. The LST mission plans to "rewrite the book" on cryo-thermal testing and modeling techniques, and validate modeling techniques to scale to future space telescopes such as SAFIR.

DiPirro, Michael↗
NASA NTRS2016

A Quasi-Global Approach to Improve Day-Time Satellite Surface Soil Moisture Anomalies through the Land Surface Temperature Input

Passive microwave observations from various spaceborne sensors have been linked to the soil moisture of the Earth's surface layer. A new generation of passive microwave sensors are dedicated to retrieving this variable and make observations in the single theoretically optimal L-band frequency (1-2 GHz). Previous generations of passive microwave sensors made observations in a range of higher frequencies, allowing for simultaneous estimation of additional variables required for solving the radiative transfer equation. One of these additional variables is land surface temperature, which plays a unique role in the radiative transfer equation and has an influence on the final quality of retrieved soil moisture anomalies. This study presents an optimization procedure for soil moisture retrievals through a quasi-global precipitation-based verification technique, the so-called Rvalue metric. Various land surface temperature scenarios were evaluated in which biases were added to an existing linear regression, specifically focusing on improving the skills to capture the temporal variability of soil moisture. We focus on the relative quality of the day-time (01:30 pm) observations from the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E), as these are theoretically most challenging due to the thermal equilibrium theory, and existing studies indicate that larger improvements are possible for these observations compared to their night-time (01:30 am) equivalent. Soil moisture data used in this study were retrieved through the Land Parameter Retrieval Model (LPRM), and in line with theory, both satellite paths show a unique and distinct degradation as a function of vegetation density. Both the ascending (01:30 pm) and descending (01:30 am) paths of the publicly available and widely used AMSR-E LPRM soil moisture products were used for benchmarking purposes. Several scenarios were employed in which the land surface temperature input for the radiative transfer was varied by imposing a bias on an existing regression. These scenarios were evaluated through the Rvalue technique, resulting in optimal bias values on top of this regression. In a next step, these optimal bias values were incorporated in order to re-calibrate the existing linear regression, resulting in a quasi-global uniform LST relation for day-time observations. In a final step, day-time soil moisture retrievals using the re-calibrated land surface temperature relation were again validated through the Rvalue technique. Results indicate an average increasing Rvalue of 16.5%, which indicates a better performance obtained through the re-calibration. This number was confirmed through an independent Triple Collocation verification over the same domain, demonstrating an average root mean square error reduction of 15.3%. Furthermore, a comparison against an extensive in situ database (679 stations) also indicates a generally higher quality for the re-calibrated dataset. Besides the improved day-time dataset, this study furthermore provides insights on the relative quality of soil moisture retrieved from AMSR-E's day- and night-time observations.

soil moisture↗
DOE OSTI2025

Analysis of anion exchange membrane water electrolyzer performance and its evolution over time

Understanding water, evolved gas, and ionic transport in membrane-electrode-assemblies (MEAs) is essential for the development of high performance and durable anion exchange membrane water electrolyzers (AEMWEs). This study evaluates the MEA conditioning process, operating conditions, and short-term stability in a 1 M potassium hydroxide (KOH) electrolyte, focusing on the underlying transport phenomena. We observe a significant initial voltage loss in continuous cell operation, which could be associated with gas bubble accumulation, transport layer or flow field passivation, and changes in the catalyst oxidation state. Further, we investigate the effects of materials and operational configurations, including the membrane type and thickness, and the electrolyte flow rate, including KOH being fed to both electrodes as well as to the anode only. Furthermore, the effect of membrane drying temperature on ex situ as well as in situ electrochemical performance is evaluated. Finally, we discuss 700 h of AEMWE operation at 1 A/cm 2 , highlighting the underlying degradation phenomena.

25 ENERGY STORAGE↗
DOE OSTI2022

Decoupling mass transport and electron transfer by a double-cathode structure of a Li-O 2 battery with high cyclic stability

Aprotic lithium-oxygen (Li-O 2 ) batteries have attracted extensive attention due to their ultrahigh theoretical energy density. However, slow and undesired electron transfer during cathodic reactions causes low cyclic stability in these batteries. Here, in this paper, we demonstrate that O 2 mass transport and electron transfer for cathodic reactions in Li-O 2 batteries could be decoupled by a double-cathode structure that efficiently enables stable electron transfer between the cathode and Li 2 O 2 /O 2 . This resolves various side reactions and slow Li 2 O 2 reaction kinetics issues in conventional Li-O 2 batteries, leading to stable operation of the cell for nearly 2 months at a capacity of 0.2 and 5 mAh cm -2 , with more than 4- and 10-fold increases in cycle life when compared with single-cathode batteries. These remarkable improvements in the cyclic stability of Li-O 2 batteries with double cathodes provide an interesting concept for improving the operational stability of other metal-rechargeable batteries with conversion-type chemistry.

25 ENERGY STORAGE↗
DOE OSTI2022

Diffusional lithium trapping as a failure mechanism of aluminum foil anodes in lithium-ion batteries

Aluminum foils are an appealing anode for lithium-ion batteries due to high capacity and low-cost, but their viability has been limited due to poor cyclability arising from pulverization and solid-electrolyte interphase growth. Here, we show that significant capacity degradation of aluminum foil anodes during electrochemical cycling also occurs due to diffusional lithium trapping. Scanning electron microscopy of cross-sectioned, cycled foils in the delithiated state reveals large regions of β-LiAl that are passivated by a surface layer of α-Al, which has poor Li + diffusivity. It is found that lithium diffusion occurs preferentially along the β-LiAl grain boundaries, so the grain structure after initial lithiation significantly affects the trapping behavior. Diffusional lithium trapping is exacerbated by both higher delithiation rates and higher areal capacity, presenting a challenge towards commercialization of aluminum foil anodes. We further demonstrate that diffusional trapping in aluminum foil anodes can be mitigated through alloy design, with the addition of 2–3 wt% Li yielding improved first cycle efficiency, and the addition of 1 wt% Si yielding improved cycle life. These results provide a mechanistic understanding of diffusional lithium trapping in aluminum foil anodes and highlight compositional design of alloys as a promising strategy to overcome it.

25 ENERGY STORAGE↗
DOE OSTI2021

Interfacial stabilization for inverted perovskite solar cells with long-term stability

Perovskite solar cells (PSCs) commonly exhibit significant performance degradation due to ion migration through the top charge transport layer and ultimately metal electrode corrosion. Here, we demonstrate an interfacial management strategy using a boron chloride subphthalocyanine (Cl 6 SubPc)/fullerene electron-transport layer, which not only passivates the interfacial defects in the perovskite, but also suppresses halide diffusion as evidenced by multiple techniques, including visual element mapping by electron energy loss spectroscopy. As a result, we obtain inverted PSCs with an efficiency of 22.0% (21.3% certified), shelf life of 7000 h, Τ 80 of 816 h under damp heat stress (compared to less than 20 h without Cl 6 SubPc), and initial performance retention of 98% after 2000 h at 80 °C in inert environment, 90% after 2034 h of illumination and maximum power point tracking in ambient for encapsulated devices and 95% after 1272 h outdoor testing ISOS-O-1. Our strategy and results pave a new way to move PSCs forward to their potential commercialization solidly.

14 SOLAR ENERGY↗
DOE OSTI2023

Heavy ion irradiation induced failure of gallium nitride high electron mobility transistors: effects of in-situ biasing

Abstract While radiation is known to degrade AlGaN/GaN high-electron-mobility transistors (HEMTs), the question remains on the extent of damage governed by the presence of an electrical field in the device. In this study, we induced displacement damage in HEMTs in both ON and OFF states by irradiating with 2.8 MeV Au 4+ ion to fluence levels ranging from 1.72 × 10 10 to 3.745 × 10 13 ions cm −2 , or 0.001–2 displacement per atom (dpa). Electrical measurement is done in situ , and high-resolution transmission electron microscopy (HRTEM), energy dispersive x-ray (EDX), geometrical phase analysis (GPA), and micro-Raman are performed on the highest fluence of Au 4+ irradiated devices. The selected heavy ion irradiation causes cascade damage in the passivation, AlGaN, and GaN layers and at all associated interfaces. After just 0.1 dpa, the current density in the ON-mode device deteriorates by two orders of magnitude, whereas the OFF-mode device totally ceases to operate. Moreover, six orders of magnitude increase in leakage current and loss of gate control over the 2-dimensional electron gas channel are observed. GPA and Raman analysis reveal strain relaxation after a 2 dpa damage level in devices. Significant defects and intermixing of atoms near AlGaN/GaN interfaces and GaN layer are found from HRTEM and EDX analyses, which can substantially alter device characteristics and result in complete failure.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1986

High-efficiency silicon solar cells - Development, current issues and future directions

This paper provides a review of material, process, and design considerations that are essential for achieving high-efficiency silicon solar cells. It describes an approach that resulted in 18.0-18.5-percent-efficient cells on low-resistivity float-zone silicon material. It is shown experimentally that a combination of surface passivation and double-layer antireflection coating can provide 2-3 percent (absolute) improvement in cell efficiency provided the material, process and cell design are carefully selected.

Rohatgi, A.↗
NASA NTRS1988

GaAs/GaAlAs distributed Bragg reflector laser with a focused ion beam, low dose dopant implanted grating

The performance of a GaAs/GaAlAs distributed Bragg reflector (DBR) laser using a focused ion beam implanted grating (FIB-DBR) is reported for the first time. Stripes of Si(2+) with a period of 2300 A and a dose about 10 to the 14th/sq cm are directly implanted into the passive large optical cavity layer to provide the distributed feedback. Surface-emitting light from the second-order grating is observed. Threshold current of 110 mA and single DBR mode operation from 20 to 40 C are obtained. The wavelength tuning rate with temperature is 0.8 A/C. The coupling coefficient is estimated to be 15/cm. The results show that FIB technology is practical for distributed feedback and DBR lasers and optoelectronic integrated circuits.

Wu, M. C.↗
NASA NTRS1989

Microwave remote sensing and radar polarization signatures of natural fields

Theoretical models developed for simulation of microwave remote sensing of the Earth surface from airborne/spaceborne sensors are described. Theoretical model calculations were performed and the results were compared with data of field measurements. Data studied included polarimetric images at the frequencies of P band, L band, and C band, acquired with airborne polarimeters over a agricultural field test site. Radar polarization signatures from bare soil surfaces and from tree covered fields were obtained from the data. The models developed in this report include: (1) Small perturbation model of wave scatterings from randomly rough surfaces, (2) Physical optics model, (3) Geometrical optics model, and (4) Electromagnetic wave scattering from dielectric cylinders of finite lengths, which replace the trees and branches in the modeling of tree covered field. Additionally, a three-layer emissivity model for passive sensing of a vegetation covered soil surface is also developed. The effects of surface roughness, soil moisture contents, and tree parameters on the polarization signatures were investigated.

Mo, Tsan↗
NASA NTRS1999

Hybrid Thermal Control Testing of a Cryogenic Propellant Tank

This report presents the experimental results of a hybrid thermal control system, one that integrates a passive system (multi-layer insulation) with an active system (a mechanical cyrocooler) applied to cryogenic propellant storage. These experiments were performed on a 1.39 m diameter spherical propellant tank filled with LH2 while installed in an evacuated chamber. The tank heat transfer to the cryocooler was accomplished with a condenser installed in the ullage of the tank and mated to the second stage of the cooler, and by conduction, through copper leaves mated to the first stage of the cooler. The first hybrid system test was performed with both the condenser and the leaves, a configuration that had excess capacity to remove the heat entering the tank; the second test was performed with only the condenser, with a capacity closely matched to the tank heating rate. In both of these tests, the goal of zero boil-off was achieved.

Plachta, David W.↗
NASA NTRS2011

Large-Scale Low-Boom Inlet Test Overview

This presentation provides a high level overview of the Large-Scale Low-Boom Inlet Test and was presented at the Fundamental Aeronautics 2011 Technical Conference. In October 2010 a low-boom supersonic inlet concept with flow control was tested in the 8'x6' supersonic wind tunnel at NASA Glenn Research Center (GRC). The primary objectives of the test were to evaluate the inlet stability and operability of a large-scale low-boom supersonic inlet concept by acquiring performance and flowfield validation data, as well as evaluate simple, passive, bleedless inlet boundary layer control options. During this effort two models were tested: a dual stream inlet intended to model potential flight hardware and a single stream design to study a zero-degree external cowl angle and to permit surface flow visualization of the vortex generator flow control on the internal centerbody surface. The tests were conducted by a team of researchers from NASA GRC, Gulfstream Aerospace Corporation, University of Illinois at Urbana-Champaign, and the University of Virginia

Hirt, Stefanie↗