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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

A bioinspired approach for adaptive solid-solid phase change material coatings with optimized surface features for passive thermal regulation

The necessity to reduce global energy consumption calls for innovative strategies in building thermal management. Passive thermal regulation, particularly through bio-inspired designs, offers a promising avenue by mimicking nature's efficient control of optical properties. This research introduces a novel, climate-responsive coating that integrates optimized bio-inspired surface features with a solid-solid phase change material (SS-PCM) to dynamically manage solar absorptivity without adding additional thickness, enabling both heating and cooling as needed. Drawing on the photonic architectures of the Saharan silver ant and Morpho Didius butterfly, we employed a modeling and multi-objective optimization framework to tailor these surface features. Simulations reveal that surface texture, rather than the intrinsic phase transition of the SS PCM, dominates optical control. Relative to a flat SS PCM coating, optimized isotropic random roughness and broader range features yielded the highest passive heating power increase of about 144 % and 319 % respectively suitable for cold climates. Saharan ant-inspired features enhanced passive cooling for hot climates, achieving a 21.8 % improvement. For moderate climates, Butterfly-wing-inspired surface features provided a balanced enhancement of 19 % for heating and 7 % for cooling. Across all cases, the optimized surface features reduced combined heating and cooling energy demand more effectively than the baseline coating, while preserving material thickness. These findings demonstrate that climate-adaptive, optimized bio-inspired surface features can unlock the full potential of SS PCM coatings, providing a versatile pathway to significant energy savings in buildings and other applications. The methodology establishes a framework for designing next-generation adaptive envelopes that leverage natural photonic principles for high-impact, low-cost thermal regulation.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Climate-Specific Passive Building Standards

Passive design principles (super insulation, airtight envelopes, elimination of thermal bridges, etc.) - pioneered in North America in the 70s and 80s and refined in Europe in the 90s have proven to be universally effective to significantly reduce heating and cooling loads. However, a single, rigid performance metric developed in Germany has led to limited uptake of passive building principles in many regions of the United States. It has also, in many cases, promoted some design decisions that had negative effects on economic feasibility and thermal comfort. This study's main objective is to validate (in a theoretical sense) verifiable, climate-specific passive standards and space conditioning criteria that retain ambitious, environmentally-necessary energy reduction targets and are economically feasible, such standards provide designers an ambitious but achievable performance target on the path to zero.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2025

Develop Accurate Techniques for Passive SiC Temperature Monitoring of Miniature Samples for Cross-Cutting Applications

Passive thermometry is critically important because most fuels and materials irradiation experiments are not instrumented, and it is necessary to understand the irradiation temperature to properly interpret any post-irradiation examination data, including evolving properties and/or microstructures. The standard passive thermometry approach uses continuous dilatometry to evaluate changes in the instantaneous coefficient of thermal expansion during post-irradiation thermal annealing. This approach has limitations in terms of sample size (minimum length requirements) and the maximum irradiation temperature that can be accurately determined, which is limited by the reduced swelling (and therefore recovery) following higher temperature irradiation and limitations on the furnaces used with push-rod dilatometers. This work evaluates two new proposed techniques for post-irradiation evaluation of passive SiC temperature monitors: differential scanning calorimetry (DSC) and Raman spectroscopy. DSC is an extremely sensitive technique that can be used for any specimen geometry and is capable of higher temperature operation. Raman spectroscopy is similar in that it is a surface technique capable of examining extremely small samples (submillimeter), can be used with a heated stage up to 1,500°C (planned for future work), and is capable of mapping local irradiation temperatures throughout a sample. Existing SiC samples that were previously irradiated over a wide range of temperatures were cut into multiple pieces to allow for annealing studies using multiple different techniques: dilatometry, DSC, and Raman spectroscopy. This approach mitigates the concern that samples analyzed using one technique may have a slightly different irradiation history than those analyzed using a different technique. Recovery was clearly observed during annealing using both DSC and dilatometry. In some cases, a direct comparison could not be made due to some of the DSC runs accidentally including material from multiple specimens and issues with using an alternative DSC sample holder for the highest temperature annealing studies. Nevertheless, one trend was clear: the DSC runs resulted in higher irradiation temperatures compared to those of the dilatometry runs. Part of this could be attributed to the higher temperature ramp rates used during the DSC runs, which are often preferred to reduce noise in the measurements. By comparison, dilatometry has previously been shown to produce better data at lower ramp rates. Future work should further investigate the ideal ramp rate for both techniques to produce consistent results. Additional work should evaluate the best holder material to use for DSC runs exceeding 1,000°C to provide reliable data while preventing interactions between SiC and the holder.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Templated Growth and Passivation of Vertically Oriented Antimony Selenide Thin Films for High-Efficiency Solar Cells in Substrate Configuration

Antimony selenide (Sb 2 Se 3 ) is a promising low-cost photovoltaic material with a 1D crystal structure. The grain orientation and defect passivation play a critical role in determining the performance of polycrystalline Sb 2 Se 3 thin-film solar cells. In this work, a seed layer is introduced on a molybdenum (Mo) substrate to template the growth of a vertically oriented, columnar Sb 2 Se 3 absorber layer by closed space sublimation. By controlling the grain orientation and compactness of the Sb 2 Se 3 seeds, obtain high-quality Sb 2 Se 3 absorber layers with passive Sb 2 Se 3 /Mo interfaces is obtained, which in turn improve the transport of photoexcited charge carriers through the absorber layer and its interfaces. Post-deposition annealing of absorber layers in ambient air is further utilized to passivate the defects in Sb 2 Se 3 and enhance the quality of the front heterojunction. As a result of systematic processing optimization, Sb 2 Se 3 planar heterojunction solar cells are fabricated in substrate configuration with a champion power conversion efficiency of 8.5%.

14 SOLAR ENERGY↗
DOE OSTI2019

Simultaneous Bottom-Up Interfacial and Bulk Defect Passivation in Highly Efficient Planar Perovskite Solar Cells using Nonconjugated Small-Molecule Electrolytes

Recent perovskite solar cell (PSC) advances have pursued strategies for reducing interfacial energetic mismatches to mitigate energy losses, as well as to minimize interfacial and bulk defects and ion vacancies to maximize charge transfer. In this work, nonconjugated multi-zwitterionic small-molecule electrolytes (NSEs) are introduced, which act not only as charge-extracting layers for barrier-free charge collection at planar triple cation PSC cathodes but also passivate charged defects at the perovskite bulk/interface via a spontaneous bottom-up passivation effect. Implementing these synergistic properties affords NSE-based planar PSCs that deliver a remarkable power conversion efficiency of 21.18% with a maximum V OC = 1.19 V, in combination with suppressed hysteresis and enhanced environmental, thermal, and light-soaking stability. Thus, this work demonstrates that the bottom-up, simultaneous interfacial and bulk trap passivation using NSE modifiers is a promising strategy to overcome outstanding issues impeding further PSC advances.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Microwave Annealing for Fast and Effective Hydrogen Activation in Polycrystalline Silicon Passivating Contacts

Hydrogenation is a crucial step in the fabrication of high-efficiency silicon solar cells. In this study, the effectiveness of hydrogen activation is demonstrated via microwave annealing of hydrogen-rich dielectrics coated on poly-Si passivating contacts. This method is compared with conventional hydrogenation techniques, such as annealing in N2 in the presence of a hydrogen-rich source (such as hydrogenated aluminum oxide (AlOx:H), hydrogenated silicon nitride (SiNy:H), or a AlOx:H/SiNy:H stack). Key improvements observed include a reduction in J0 from 30 to <5 fA cm-2, an increase in iVoc from 690 to >730 mV, and an enhancement in effective lifetime (teff) from 0.6 to ~3.5 milliseconds on phosphorus-doped poly-Si/SiO2 passivating contact samples. With a very short annealing time of ~1-2 min, the samples passivated by AlOx:H, SiNy:H, or the stack show similar performance to samples subjected to 30 min of nitrogen annealing. Photoluminescence (PL) spectra corroborate the findings regarding the hydrogenation of the poly-Si layer and the c-Si substrate, with an increase in PL intensity after microwave annealing. Ultimately, this work suggests that microwave annealing could be a promising addition, offering flexibility to traditional firing hydrogenation processes.

hydrogenation↗
DOE OSTI2019

Hydrogenation Mechanisms of Poly-Si/SiO x Passivating Contacts by Different Capping Layers

Herein, posttreatment techniques of phosphorus-doped poly-Si/SiO x passivating contacts, including forming gas annealing (FGA), atomic layer deposition (ALD) of hydrogenated aluminum oxide (AlO x :H), and plasma-enhanced chemical vapor deposition (PECVD) of hydrogenated silicon nitride (SiN x :H), are investigated and compared in terms of their application to silicon solar cells. A simple FGA posttreatment produces a significant increase in the implied open circuit voltage (iV oc ) and the effective minority-carrier lifetime (teff) of high-resistivity crystalline Si (c-Si) samples, whereas low-resistivity samples show a minimal change. Treatment by means of AlO x :H and/or SiN x :H followed by postdeposition FGA results in a universal increase in t eff and iV oc for all substrate resistivities (as high as 12.5 ms and 728 mV for 100 Ω cm and 5.4 ms and 727 mV for 2 Ω cm n-type c-Si substrates). In addition, both the FGA and AlO x :H + FGA techniques can inject sufficient hydrogen into the samples to passivate defects at the SiO x /c-Si and poly-Si/SiO x interfaces. However, this hydrogen concentration is insufficient to neutralize both the nonradiative defects inside the poly-Si films and dangling bonds associated with the amorphous Si phase present in them. The hydrogen injected by the SiN x :H + FGA technique can passivate both the interfaces and the defects and dangling bonds within the poly-Si film. These results are confirmed by low-temperature photoluminescence spectroscopy, Fourier transform infrared spectroscopy, and dynamic secondary-ion mass spectrometry measurements.

14 SOLAR ENERGY↗
DOE OSTI2021

Investigation of Gallium–Boron Spin-On Codoping for poly-Si/SiO x Passivating Contacts

A doping technique for p-type poly-Si/SiOx passivating contacts using a spin-on method for different mixtures of Ga and B glass solutions is presented. Effects of solution mixing ratios on the contact performance (implied open circuit voltage iV oc , contact resistivity ..rho..c) are investigated. For all as-annealed samples at different drive-in temperatures, increasing the percentage of Ga in the solution shows a decrement in iV oc (from ~680 to ~610 mV) and increment in ..rho..c (from ~3 to ~800 mO cm 2 ). After a hydrogenation treatment by depositing a SiN x /AlO x stack followed by forming gas annealing, all samples show improved iVoc (~700 mV with Ga-B co-doped, and ~720 mV with all Ga). Interestingly, when co-doping Ga with B, even a small amount of B in the mixing solution shows negative effects on the surface passivation. Active and total dopant profiles obtained by electrical capacitance voltage and secondary-ion mass spectrometry measurements, respectively, reveal a relatively low percentage of electrically-active Ga and B in the poly-Si and Si layers. Overall, these results help understand the different features of the two dopants: a low ρ c with B, a good passivation with Ga, their degree of activation inside the poly-Si and Si layers, and the annealing effects.

14 SOLAR ENERGY↗
DOE OSTI2018

Effects of four-mode hydrothermal aging on three-way catalysts for passive selective catalytic reduction to control emissions from lean-burn gasoline engine

Passive selective catalytic reduction (SCR) is a promising approach for the control of NOX emissions in lean burn gasoline exhausts. It requires ammonia (NH 3 ) to be produced over a three-way catalyst (TWC) during periods of fuel-rich operation for the reduction of NO X during periods of fuel-lean operation. Previous research has shown the viability of this system but has not examined the effects of hydrothermal degradation. This work is focused on evaluating the effects of hydrothermal aging on the TWC in a passive SCR system. Two catalysts were studied: a Pd-TWC, and a NO X storage and reduction (NSR) TWC. Samples were aged at 920 °C for 100 h using a four-mode hydrothermal aging procedure. This causes the catalyst to be oxidized and reduced, as it would in a real system. The effects of aging were evaluated using simulated exhaust under both steady state and lean-rich cycling conditions. Hydrothermal aging caused significant changes in catalyst activity, leading to a decrease in low temperature conversion of carbon monoxide (CO) and propane (C 3 H 8 ) on both catalysts, and degradation of oxygen storage and NO X storage components. Furthermore, the catalysts maintained their activity for NO X conversion and NH 3 production, showing sufficient activity for the operation of a passive SCR with an optimum projected fuel consumption of 92–98% compared to stoichiometric operation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Investigation of the ordered and disordered corrosion morphologies on Ni-based alloy in the passive state

We report an order and disorder combined corrosion morphology of dual-phase Ni-based alloy in the passive state. After galvanostatic polarization in the passive region, the surface of the γ(Ni) phase presents amorphous feature while that of the γ′(Ni 3 Al) phase maintains crystalline. The variations in weight percentages of Ni (50.19% → 3.80%), Co (19.24% → 0.65%), Ta (0.85% → 21.19%), and W (5.73% → 43.79%) of γ surface are evident, whereas the composition of γ′ surface is nearly unchanged. The passive film comprises $W^{6+}_{ox}$, $Ta^{5+}_{ox}$, $Cr^{3+}_{ox}$, $Co^{8/3+}_{ox}$, $Ni^{2+}_{hy}$, and $Co^{2+}_{hy}$, and it shows stronger protection effect on the γ phase.

Density functional theory↗
DOE OSTI2023

Pinhole electrical conductivity in polycrystalline Si on locally etched SiN$_y$/SiO$_x$ passivating contacts for Si solar cells

State-of-the-art monocrystalline Si (c-Si) solar cells require passivating contacts to achieve a high degree of charge-carrier separation and collection. In this work, we focus on boron-doped polycrystalline Si on locally etched silicon nitride/silicon oxide (PLENO) passivating contacts. In PLENO contacts, excellent surface passivation is provided by the ~10 nm dielectric bilayer, while pinholes in the dielectric bilayer, that are filled with doped polycrystalline Si, provide charge-carrier selectivity and transport. During PLENO fabrication, etch undercut in the dielectric bilayer occurs. Here, using electrical characterization and microscopies, we show that undercut causes pinholes to be electrically resistive in PLENO. A processing sequence that eliminates the undercut in the final PLENO structure results in electrically conductive pinholes with low contact resistivity.

14 SOLAR ENERGY↗
DOE OSTI2023

Eco-friendly passive radiative cooling using recycled packaging plastics

Passive daytime radiative cooling, requiring zero external energy consumption, is a promising cooling strategy achieved by simultaneously reflecting solar irradiance and thermally radiating heat into the cold outer space (~3 K) through the atmospheric transparency window. However, current materials for passive radiative cooling face huge challenges, such as complicated fabrication approaches, expensive raw materials, and environmental requirements for practical applications. In line with the urgent need for plastic recycling to curb global environmental pollution, the recycled plastics are used to fabricate a passive radiative cooling material. Herein, the foam-paper composite (FPC) with excellent self-cooling capability is fabricated by a simple crushing-and-mixing procedure using recycled polystyrene (PS) foam and printer paper. The superhydrophobic PS foam particles not only protect the FPC from water damage for field applications but also reinforce its solar reflectivity via their porous structure. The cellulose fibers in printer paper can efficiently emit infrared thermal radiation into the cold outer space and bond dispersed PS foam particles together, further increasing its mechanical strength. The combination of highly diffusely reflective PS foam particles and fiber-based printer paper results in a reflectivity of 96% in the solar spectrum, a sub-ambient cooling performance of 8.4 degrees C, and a maximum radiative cooling power of 90 W/m2 during a 24-h cycle. Meanwhile, the FPC with high humidity can maintain its high solar reflectivity, which promotes its application in humid subtropical areas. Further, the low material cost and ease of fabrication will provide a path for effective daytime radiative cooling, especially in less developed areas.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2016

Low-cost plasma immersion ion implantation doping for Interdigitated back passivated contact (IBPC) solar cells

Here, we present progress to develop low-cost interdigitated back contact solar cells with pc-Si/SiO 2 /c-Si passivated contacts formed by plasma immersion ion implantation (PIII). PIII is a lower-cost implantation technique than traditional beam line implantation due to its simpler design, lower operating costs, and ability to run high doses (1E14-1E18 cm -2 ) at low ion energies (20 eV-10 keV). These benefits make PIII ideal for high throughput production of patterned passivated contacts, where high-dose, low-energy implantations are made into thin (20-200 nm) a-Si layers instead of into the wafer itself. For this work symmetric passivated contact test structures (~100 nm thick) grown on n-Cz wafers with pH3 PIII doping gave implied open circuit voltage (iV oc ) values of 730 mV with J o values of 2 fA/cm 2 . Samples doped with B 2 H 6 gave iV oc values of 690 mV and J o values of 24 fA/cm 2 , outperforming BF 3 doping, which gave iV oc values in the 660-680 mV range. Samples were further characterized by SIMS, photoluminescence, TEM, EELS, and post-metallization TLM to reveal micro- and macro-scopic structural, chemical and electrical information.

14 SOLAR ENERGY↗
DOE OSTI2018

Charge carrier transport mechanisms of passivating contacts studied by temperature-dependent J-V measurements

The charge carrier transport mechanism of passivating contacts which feature an ultra-thin oxide layer is investigated by studying temperature-dependent current-voltage characteristics. 4-Terminal dark J-V measurements at low temperatures reveal non-linear J-V characteristics of passivating contacts with a homogeneously grown silicon oxide, which result in an exponential increase in contact resistance towards lower temperature. The attempt to describe the R(T) characteristic solely by thermionic emission of charge carriers across an energy barrier leads to a significant underestimation of the resistance by several orders of magnitude. However, the data can be described properly with the metal-insulator-semiconductor (MIS) theory if tunneling of charge carriers through the silicon oxide layer is taken into account. Furthermore, temperature-dependent light J-V characteristics of solar cells featuring passivating contacts at the rear revealed a FF drop at T < 205 K, which is near the onset temperature of the exponential increase in contact resistivity.

14 SOLAR ENERGY↗
DOE OSTI2020

Deposition pressure dependent structural and optoelectronic properties of ex-situ boron-doped poly-Si/SiO x passivating contacts based on sputtered silicon

Among common methods to form polycrystalline silicon (poly-Si) films for passivating-contact solar cells, physical vapor deposition, in particular sputtering, is the safest one as it does not require any toxic gaseous precursors. One of the critical parameters to control the properties of sputtered silicon films is their deposition pressure. In this work, structural and optoelectronic characteristics of ex-situ boron-doped poly-Si/SiO x passivating contacts, formed from sputtered intrinsic amorphous silicon (a-Si) deposited at different pressures on top of SiO x /c-Si substrates and subjected to a high-temperature boron diffusion step, are investigated. The deposition rate and density of the as-deposited a-Si films increase with reducing pressure. Low-temperature photoluminescence spectra captured from the as-deposited samples at different pressures do not show typical emissions from hydrogenated a-Si. Meanwhile, their Fourier-transform infrared absorption spectra all show Si–H stretching modes, indicating that hydrogen had been initially incorporated into the chemical SiO x layers and eventually hydrogenated the a-Si/SiO x interfaces during the sputtering process. After the high-temperature boron-diffusion step, all hydrogen-related peaks disappear. Lower pressure films (1.5 and 2.5 mTorr) show more consistent improved performance after hydrogen treatments, compared to higher pressure films (4 and 5 mTorr). Overall, the resultant passivating contacts at 2.5 mTorr achieve a low single-side recombination current density Jo of ~9 fA/cm 2 , whereas their contact resistivity is still low at 15 mO cm 2 .

14 SOLAR ENERGY↗
DOE OSTI2020

Reactive ion etched, self-aligned, selective area poly-Si/SiO 2 passivated contacts

Front/back poly-Si/SiO 2 contact devices suffer from low short-circuit current density, J sc , due to parasitic optical absorption in the front poly-Si layer. Thin poly-Si (~20 nm) allows for high J sc but is not compatible with screen-printed fire-through contacts. We therefore study the effects of post-deposition etching of a thick poly-Si (200 nm) front layer by reactive ion etching (RIE) using the metal grid lines as a self-aligned mask. We show that passivation is maintained in the device during RIE and that J sc is increased by a gain in the blue quantum efficiency response. However, our specific etching parameters cause non-uniform etching of the poly-Si leading to premature loss of passivation without optimal gain in J sc . Etched, unpassivated layers can be re-passivated with a H-containing dielectric layer leading to a gain in Jsc, open circuit voltage, V oc , Fill-Factor, FF, and efficiency.

14 SOLAR ENERGY↗
DOE OSTI2022

Significant improvement of conversion efficiency by passivation of low-angle grain boundaries in flexible low-cost single-crystal-like GaAs thin-film solar cells directly deposited on metal tape

We develop an easily implementable yet effective process to achieve high power conversion efficiency in newly-developed flexible single-crystal-like GaAs thin-film photovoltaic solar cells on cheap metal tape. We study various techniques on the fabricated devices to passivate the defect states associated with dangling bonds at low-angle grain boundaries (LA-GBs) existing in the single-crystal-like GaAs material. We report that sulfur by trioctylphosphine sulfide (TOP:S) solution treatment can partially but effectively passivate the defect states at the LA-GBs to increase all the solar cell performance parameters of open-circuit voltage VOC (33.2%), short-circuit current JSC (19.5%), and fill factor FF (25.8%), resulting in the improvement of the power conversion efficiency more than double. The material and device characterizations and numerical modeling are performed to propose a mechanism, also suggesting that the power conversion efficiency higher than 20%, which is an important target milestone in emerging solar cell technologies, can be achieved. This work presents the first effective passivation of the bulk defects in GaAs at the device level and can also offer a solution for other photonic and electronic devices using non-single-crystalline GaAs films for flexible electronics.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Mitigation of shunt in poly -Si/SiO$_{x}$ passivated interdigitated back contact monocrystalline Si solar cells by self-aligned etching between doped fingers

Polycrystalline silicon on silicon oxide (poly-Si/SiO x ) passivating contacts can be used for ultra-high-efficiency interdigitated back contact (IBC) monocrystalline silicon solar cells. We evaluate the use of intrinsic poly-Si for the region that isolates the p- and n-type fingers at the back side of IBC devices. To mitigate shunt across the isolation region between the doped p- and n-type fingers, we demonstrate self-aligned subtractive processing by etching the poly-Si in the isolation region using SF6 plasma followed by etching in a tetramethylammonium hydroxide (TMAH) solution. After removal of the poly-Si, the isolation region was passivated with SiN x and Al 2 O 3 , which resulted in an 11.7% increase in the fill factor in a 19.8% efficient device. Furthermore, we evaluate the limitations of this device through Suns-V oc analysis and simulations using SunSolve and Quokka3 solar cell simulation software. Through Quokka3, we show that the most significant efficiency losses come from junction recombination current (J 02 ) in the isolation region between doped fingers. We predict that the cell efficiency can be most improved with reduced J 02 through better isolation of heavily doped fingers by etching the isolation region deeper into the bulk or through enhanced surface chemical passivation in this region.

14 SOLAR ENERGY↗