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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Loss Analysis and Performance Optimization Pathways of 729-mV VocSi Solar Cells with Poly-Si on Locally-Etched Dielectric Passivating Contacts

In this article, the performance analysis of a 22.5% efficient polysilicon on silicon oxide (poly-Si/SiOx) passivated contact solar cells with deliberately introduced pinholes using metal-assisted chemical etching (MACE) has been performed with the help of optical analysis using Sunsolve and electrical analysis using Quokka3. The power loss is maximum due to recombination and resistive losses in the bulk (~0.76 mW/cm2 ) followed by power loss due to rear contact recombination (~0.35 mW/cm2 ). Recombination at the front surface also contributes to 0.24 mW/cm2. The effect of improving the bulk lifetime and lowering the recombination current density at the rear side on Voc, FF and efficiency has been investigated.

MACE↗
DOE OSTI2026

Axion dark matter search with a photonic bandgap cavity haloscope and dielectric tuning rod over 10.25-10.45 GHz

We report the development of a new widely tunable cavity and demonstrate its use in a search for dark matter axions. We achieve unloaded quality factors above $10^{5}$, roughly $25\times$ larger than a bare copper cavity at the same frequency, using concentric sapphire shells to reduce Ohmic losses on the cavity barrel. A rotating sapphire rod tunes our cavity mode over the $10.1-11.7$ GHz range, approximately $16\%$ of its resonant frequency. Using an amplified receiver chain, we demonstrate sensitivity to new axion parameter space by tuning the cavity over the $200$ MHz range between $10.25-10.45$ GHz (42.4 - 43.2, $μ$eV) to constrain the axion-to-photon coupling to $|g_{aγγ}|$$\leq$ 1 $\times$$10^{-12}$${GeV}^{-1}$. This cavity can scan its tuning range about $9$ times faster compared to a bare copper cavity when paired with a photon counting device, laying the groundwork for a definitive search for the QCD axion over $10.1-11.7$ GHz.

Lynn, Morgan [Chicago U.]↗
DOE OSTI2021

Charge Trapping in Polymer Electrets with Highly Dilute Blended Arylamine Donors

The nature of and ability to control biasing across dielectrics is a key area of research for the design of more versatile organic field-effect transistors (OFETs). One important technique to achieve such control is the inclusion of donor or acceptor molecules in the dielectric to modulate charge trapping therein. Here in this work, we report the effects of the additive concentration on OFETs with two different arylamines blended in polystyrene (PS) dielectrics, N,N'-diphenyl-N,N'-di-p-tolylbenzene-1,4-diamine (MPDA) and 4-anilinotriphenylamine (PATPA), as well as a comparison between PATPA/PS blends and dielectrics where PATPA was chemically tethered to the PS matrix. Dielectrics included in OFETs were subject to charging, and their charging capacity and stability were extracted from the OFET threshold voltages. For both MPDA/PS and PATPA/PS, blends with additive mole fractions as low as χ = 3 × 10 –4 were sufficient to cause increases in the charge trapping relative to pure PS dielectrics. We observed a pronounced inverse relationship between the capacity and stability of blended systems at larger mole fractions (χ = 10 –2 ) where the interadditive molecule distances became comparable to their size (~1 nm). Differences between MPDA and PATPA behaviors were consistent with their different structures and sizes. Furthermore, we found a small effect on electronic trapping arising from the chemical tethering of PATPA to the PS matrix. This result was consistent with the changes made to the additive during the tethering process and small compared to the observed differences arising from the concentration. These results suggest that the average intermolecular separation is a key determinant of charge storage stability in blended dielectrics.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Exploding foil initiator

An exploding foil initiator assembly is provided comprising a first layer of dielectric material, a second layer of dielectric material, a third layer of dielectric material, and a flyer. The first layer of dielectric material comprises a first pair of vias. The second layer of dielectric material comprises a first surface adjacent to the first layer of dielectric material, a second surface opposed to the first surface, a second pair of vias, and a bridge. Each of the second pair of vias extends from the first surface to the second surface and is in contact with one of the first pair of vias. The bridge is positioned on the second surface and is electrically connected to the second pair of vias. The third layer of dielectric material is positioned on the second surface of the second layer and comprises a bore positioned at least partially over the bridge forming a barrel. The flyer is positioned in the barrel on the bridge.

Krueger, Daniel Scott↗
DOE OSTI2020

Local negative permittivity and topological phase transition in polar skyrmions

Topological solitons such as magnetic skyrmions have drawn attention as stable quasi-particle-like objects. The recent discovery of polar vortices and skyrmions in ferroelectric oxide superlattices has opened up new vistas to explore topology, emergent phenomena and approaches for manipulating such features with electric fields. Using macroscopic dielectric measurements, coupled with direct scanning convergent beam electron diffraction imaging on the atomic scale, theoretical phase-field simulations and second-principles calculations, we demonstrate that polar skyrmions in (PbTiO 3 ) n /(SrTiO 3 ) n superlattices are distinguished by a sheath of negative permittivity at the periphery of each skyrmion. This enhances the effective dielectric permittivity compared with the individual SrTiO 3 and PbTiO 3 layers. Moreover, the response of these topologically protected structures to electric field and temperature shows a reversible phase transition from the skyrmion state to a trivial uniform ferroelectric state, accompanied by large tunability of the dielectric permittivity. Pulsed switching measurements show a time-dependent evolution and recovery of the skyrmion state (and macroscopic dielectric response). The interrelationship between topological and dielectric properties presents an opportunity to simultaneously manipulate both by a single, and easily controlled, stimulus, the applied electric field. Polar skyrmions are topologically protected structures that can exist in (PbTiO 3 ) n /(SrTiO 3 ) n superlattices. Here, it is shown that they have negative permittivity at the surface, and that they can undergo a reversible phase transition with large dielectric tunability under an electric field.

36 MATERIALS SCIENCE↗