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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Radiative and Nonradiative Recombinations in Organic Radical Emitters: The Effect of Guest–Host Interactions

Radical-carrying organic molecules have received significant attention to bypass the issue related to harvesting triplet excitons in current light-emitting materials. While the computational efforts conducted so far have treated these radical emitters as isolated entities, in actual devices, they are embedded in a host matrix and subject to emitter–host interactions. In this study, by combining molecular dynamics simulations and density functional theory calculations, the impact of the host matrix on the optoelectronic performance of radical emitters is evaluated, taking as a representative example the (4-ncarbazolyl-2,6-dichlorophenyl)bis(2,4,6-trichlorophenyl)-methyl (TTM-3NCz) radical emitter dispersed in a 4,4-bis(carbazol-9-yl)biphenyl (CBP) host. A morphological analysis shows that steric effects around the radical centers, carried by the TTM electron-poor moieties of the emitters, disfavor π–π interactions with the host molecules, which leads to random intermolecular orientations around the TTM moieties. The 3NCz electron-rich moieties of the emitters, however, have much lesser spatial hindrance for intermolecular π–π stacking, which modulates the structural and electronic properties of the emitters in the host matrix. The influence of dynamic and static disorders on the radiative and nonradiative recombination processes is also investigated and it is found that the rates of nonradiative recombination are small, which opens the way to 100% internal quantum efficiency for the doublet-based emission process.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Inorganic Halide Perovskitoid TlPbI 3 for Ionizing Radiation Detection

Room temperature semiconductor detector (RTSD) materials for γ-ray and X-ray radiation are in great demand for the nonproliferation of nuclear materials as well as for biomedical imaging applications. Halide perovskites have attracted great attention as emerging and promising RTSD materials. In this contribution, the material synthesis, purification, crystal growth, crystal structure, photoluminescence properties, ionizing radiation detection performance, and electronic structure of the inorganic halide perovskitoid compound TlPbI 3 are reported on. This compound crystallizes in the ABX 3 non-perovskite crystal structure with a high density of d = 6.488 g·cm –3 , has a wide bandgap of 2.25 eV, and melts congruently at a low temperature of 360 °C without phase transitions, which allows for facile growth of high quality crystals with few thermally-activated defects. High-quality TlPbI 3 single crystals of centimeter-size are grown using the vertical Bridgman method using purified raw materials. A high electrical resistivity of ≈10 12 Ω·cm is readily obtainable, and detectors made of TlPbI 3 single crystals are highly photoresponsive to Ag K α X-rays (22.4 keV), and detects 122 keV γ-rays from 57 Co radiation source. The electron mobility-lifetime product µ e τ e was estimated at 1.8 × 10 –5 cm 2 ·V –1 . A high relative static dielectric constant of 35.0 indicates strong capability in screening carrier scattering and charged defects in TlPbI 3 .

36 MATERIALS SCIENCE↗
DOE OSTI2021

Phase-Transition Interlayer Enables High-Performance Solid-State Sodium Batteries with Sulfide Solid Electrolyte

All-solid-state sodium (Na) batteries (ASSSBs) using sulfide-based solid electrolytes (SEs) have attracted intensive attention due to their superior safety, high energy density and low cost. However, interfacial issue is one of the biggest challenges to achieve high-performance sulfide-based ASSSBs due to the serious reactions between active Na metal and sulfide SEs at the interface. To address the interfacial challenges, we propose in this paper a simple and efficient approach by introducing a polymer electrolyte as an interlayer to stabilize the interface. Na 3 SbS 4 as a model sulfide SE is used to demonstrate the interlayer strategy to stabilize the interface by preventing the detrimental reactions and inhibiting Na dendrites. As a result, stable Na plating/stripping was observed in Na symmetric cells under the current density of 0.1 mA cm –2 . Moreover, ASSSBs with Na metal and TiS 2 electrode delivered long-term stability over 300 cycles remaining a specific capacity above 100 mAh g –1 , and FeS 2 ||Na cells exhibited an impressive specific capacity of up to 200 mAh g –1 after the 20th cycles. This work demonstrates an efficient strategy to address interfacial challenges between sulfide SEs and Na metal, which contributes to the development of ASSSBs in next-generation energy storage systems.

25 ENERGY STORAGE↗
DOE OSTI2021

Ferroic Halide Perovskite Optoelectronics

Metal halide perovskites (MHPs) as one of the most active materials gained tremendous attention in the past decade because of their outstanding performance in optoelectronics. Owing to their perovskite structure, ferroelectricity is anticipated in this class of materials. However, whether MHPs are ferroelectric or not remains elusive. Recently, discussion regarding ferroelasticity in MHPs has been also raised. In addition, ionic motion and structural dynamics are well known in MHPs. Additionally, the interplay of these phenomena including electric polarization, strain, ionic motion, and structural dynamics can have a significant impact on optoelectronics. Therefore, understanding the mechanism behind these phenomena and their interactions is critical in addressing the controversy about ferroicity of MHPs and developing functional devices. Here, the current findings about MHP's ferroicity are summarized and evaluated and a perspective for the future is provided. It is suggested that ionic motion and associated phenomena, coupled with ferroic behavior, are the main drivers behind MHPs functionality. The challenges are also discussed in probing MHPs’ ferroicity and what new measurement modalities are needed to fully understand and characterize MHP behavior. Finally, it is discussed how ferroic and strain can affect the optoelectronic performance of MHPs and how they can be used for engineering of higher performance devices.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Band Edge Control of Quasi–2D Metal Halide Perovskites for Blue Light–Emitting Diodes with Enhanced Performance

Perovskite light–emitting diodes (PeLEDs) have received great attention for their potential as next–generation display technology. While remarkable progress has been achieved in green, red, and near–infrared PeLEDs with external quantum efficiencies (EQEs) exceeding 20%, obtaining high performance blue PeLEDs remains a challenge. Poor charge balance due to large charge injection barriers in blue PeLEDs has been identified as one of the major roadblocks to achieve high efficiency. Here band edge control of perovskite emitting layers for blue PeLEDs with enhanced charge balance and device performance is reported. By using organic spacer cations with different dipole moments, that is, phenethyl ammonium (PEA), methoxy phenethyl ammonium (MePEA), and 4–fluoro phenethyl ammonium (4FPEA), the band edges of quasi–2D perovskites are tuned without affecting their band gaps. Furthermore, detailed characterization and computational studies have confirmed the effect of dipole moment modification to be mostly electrostatic, resulting in changes in the ionization energies of ≈0.45 eV for MePEA and ≈ –0.65 eV for 4FPEA based thin films relative to PEA–based thin films. With improved charge balance, blue PeLEDs based on MePEA quasi–2D perovskites show twofold increase of the EQE as compared to the control PEA based devices.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Rare-Earth Permanent Magnet SmCo 5 for Chiral Interfacial Spin-Orbitronics

Interfacially asymmetric magnetic multilayers made of heavy metal/ferromagnet have attracted considerable attention in the spintronics community for accommodating spin-orbit torques (SOTs) and meanwhile for hosting chiral spin textures. In these multilayers, the accompanied interfacial Dzyaloshinskii–Moriya interaction (iDMI) permits the formation of Néel-type spin textures. While significant progresses have been made in Co, CoFeB, Co 2 FeAl, CoFeGd based multilayers, it would be intriguing to identify new magnetic multilayers that could enable spin-torque controllability and meanwhile host nanoscale skyrmions. In this report, first, thin films made of permanent magnet SmCo 5 with perpendicular magnetic anisotropy are synthesized, in which the deterministic SOT switching, enabled by the spin Hall effect, in Pt/SmCo 5 /Ta trilayer is demonstrated. Further, the stabilization of room-temperature skyrmions with diameters ≈100 nm in [Pt/SmCo 5 /Ta] 15 , together with a skyrmionium-like spin texture in [Pt/SmCo 5 /Ir] 15 multilayers is shown. Based on the material specific parameters, micromagnetic simulations are also carried out. The results confirm the presence of chiral spin textures in this new material family. Through interfacial engineering, the results thus demonstrate that rare earth permanent magnets could be a new platform for studying interfacial chiral spintronics.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Head on Comparison of Self- and Nano-Assemblies of Gamma Peptide Nucleic Acid Amphiphiles

Peptide nucleic acids (PNAs) are nucleic acid analogs with hybridization properties and enzymatic stability superior to that of DNA. In addition to gene targeting applications, PNAs have garnered significant attention as bio-polymers due to the Watson–Crick-based molecular recognition and flexibility of synthesis. Here, in this work, PNA amphiphiles are engineered using chemically modified gamma PNA (8 mer in length) containing hydrophilic diethylene glycol units at the gamma position and covalently conjugated lauric acid (C12) as a hydrophobic moiety. Gamma PNA ($\gamma$PNA) amphiphiles self-assemble into spherical vesicles. Further, nano-assemblies (NA) are formulated using the amphiphilic $\gamma$PNA as a polymer via ethanol injection-based protocols. Comprehensive head-on comparison of the physicochemical and cellular uptake properties of PNA derived self- and NA is performed. Small-angle neutron and X-ray scattering analysis reveal ellipsoidal morphology of $\gamma$PNA NA that results in superior cellular delivery compate to the spherical self-assembly. Next, the functional activities of $\gamma$PNA self-and NA in lymphoma cells via multiple endpoints, including gene expression, cell viability, and apoptosis-based assays are compared. Overall, it is established that $\gamma$PNA amphiphile is a functionally active bio-polymer to formulate NA for a wide range of biomedical applications.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Benzimidazole Based Hole‐Transporting Materials for High‐performance Inverted Perovskite Solar Cells

Abstract Interfaces play a decisive role in perovskite solar cells’ power conversion efficiency and their long‐term durability. Small‐molecule hole‐transporting materials (HTMs) have grabbed enormous attention due to their structural flexibility, material properties, and stabilities, allowing for improved operational durability in perovskite photovoltaics. This study synthesizes and investigates a new class of benzimidazole‐based small molecules, named YJS001 and YJS003 , serving as the HTMs to enable high‐efficiency mixed‐cation mixed‐halide perovskite solar cells. The benzimidazole‐based materials are dopant‐free HTMs composed of donor and acceptor building blocks that are designed to engineer the energy level alignment near the HTM/perovskite interface. Mixed‐cation mixed‐halide perovskites can be grown uniformly on both HTMs with large crystalline grains. It is discovered that the donor‐rich YJS003 ‐based solar cell exhibits a high open‐circuit voltage of 1.09 V with a champion power conversion efficiency of over 20%. Power‐dependent current–voltage characteristics of the solar cells are analyzed, from which the high performance of YJS003's excellent hole mobility and well‐aligned energy level is attributed. This work introduces a new class of benzimidazole‐based small molecules as HTMs, that paves the path for dopant free interface material development for commercialization of perovskite solar cells.

14 SOLAR ENERGY↗
DOE OSTI2022

Tradeoff between Intermolecular Interaction and Backbone Disorder by High Molecular Dipole Block for Improving Blend Morphology of Polymer Solar Cells

Constructing terpolymer has attracted increasing attention as a strategy to improve the performance of polymer solar cell. Terpolymer usually offers an opportunity to lower the frontier molecular orbital energy level, introduces additional absorption band and sometimes optimizes the morphology of the active blend. Generally, the additional segment in terpolymer backbone inevitably introduces backbone disorder, which causes entropy rises. However, selecting a suitable dipole unit introduces extra driving forces for crystallization by enhancing intermolecular interactions. This provides a handy knob for tradeoff between intermolecular interaction and backbone disorder, thus regulating the blend morphology. In this study, a high dipole and electron-deficient group of pyrrolo[3,4-f ]benzotriazole-5,7(6H)-dione (TzBI) is incorporated into the high-performance donor polymer and a series of terpolymers with different content of TzBI are designed. As expected, the morphology is optimized gradually for improving charge generation and charge transport, also suppressing charge recombination. The champion device with 10% TzBI exhibited a power conversion efficiency (PCE) of 18.36%, which is 5% increase compared to the controlled device. This study presents a charming terpolymer strategy by highly electron-deficient and high dipole segment to realize a tradeoff between intermolecular interaction and backbone disorder, facilitating the optimization of morphology and elevation of fill factor and device efficiency.

36 MATERIALS SCIENCE↗
DOE OSTI2023

A Materials Perspective on Direct Recycling of Lithium-Ion Batteries: Principles, Challenges and Opportunities

As the dominant means of energy storage technology today, the widespread deployment of lithium-ion batteries (LIBs) would inevitably generate countless spent batteries at their end of life. From the perspectives of environmental protection and resource sustainability, recycling is a necessary strategy to manage end-of-life LIBs. Compared with traditional hydrometallurgical and pyrometallurgical recycling methods, the emerging direct recycling technology, rejuvenating spent electrode materials via a non-destructive way, has attracted rising attention due to its energy efficient processes along with increased economic return and reduced CO 2 footprint. This review investigates the state-of-the-art direct recycling technologies based on effective relithiation through solid-state, aqueous, eutectic solution and ionic liquid mediums and thoroughly discusses the underlying regeneration mechanism of each method regarding different battery chemistries. It is concluded that direct regeneration can be a more energy-efficient, cost-effective, and sustainable way to recycle spent LIBs compared with traditional approaches. Additionally, it is also identified that the direct recycling technology is still in its infancy with several fundamental and technological hurdles such as efficient separation, binder removal and electrolyte recovery. Finally, in addressing these remaining challenges, this review proposes an outlook on potential technical avenues to accelerate the development of direct recycling toward industrial applications.

25 ENERGY STORAGE↗
DOE OSTI2023

The Riddle of Dark LLZO: Cobalt Diffusion in Garnet Separators of Solid‐State Lithium Batteries

Abstract Solid‐state batteries (SSBs) with a Li 7 La 3 Zr 2 O 12 (LLZO) garnet electrolyte are attracting much attention as robust and safe alternative to conventional lithium‐ion batteries. Technical challenges in the practical implementation of garnet SSBs are related to the need for high‐temperature sintering, which often leads to undesirable chemical reactions with the cathode material. While these reactions are well understood for composite cathodes, very little is known about similar processes between cathode and separator during battery fabrication. This work focuses on understanding the processes between the composite LiCoO 2 ‐LLZO cathode and the LLZO separator and how they affect the battery performance. The extensive diffusion of Co‐ions within LLZO, which leads to the often‐observed LLZO darkening, is shown to have a significant impact on ionic conductivity, electronic conductivity, and dendrite stability of the separator. Experimental data coupled with large‐scale molecular dynamics simulations uncover the diffusion mechanism for Co‐ions and identify secondary phases that form during these interactions. In addition to extensive Co‐ion diffusion within the grains, a non‐uniform segregation of Co‐ions at grain boundaries is found leading to the formation of three distinct Co‐containing phases. This work offers a general approach to studying the fundamental ion diffusion processes that occur during the fabrication of oxide SSBs.

electrochemical properties↗
DOE OSTI2023

Strain Anisotropy Driven Spontaneous Formation of Nanoscrolls from 2D Janus Layers

2D Janus transition metal dichalcogenides (TMDs) have attracted attention due to their emergent properties arising from broken mirror symmetry and self‐driven polarization fields. While it has been proposed that their vdW superlattices hold the key to achieving superior properties in piezoelectricity and photovoltaic, available synthesis has ultimately limited their realization. Here, in this study, the first packed vdW nanoscrolls made from Janus TMDs through a simple one‐drop solution technique are reported. The results, including ab initio simulations, show that the Bohr radius difference between the top sulfur and the bottom selenium atoms within Janus ${M^S_{Se}}$ (M = Mo, W) results in a permanent compressive surface strain that acts as a nanoscroll formation catalyst after small liquid interaction. Unlike classical 2D layers, the surface strain in Janus TMDs can be engineered from compressive to tensile by placing larger Bohr radius atoms on top (${M_S^{Se}}$) to yield inverted C scrolls. Detailed microscopy studies offer the first insights into their morphology and readily formed Moiré lattices. In contrast, spectroscopy and FETs studies establish their excitonic and device properties and highlight significant differences compared to 2D flat Janus TMDs. These results introduce the first polar Janus TMD nanoscrolls and introduce inherent strain‐driven scrolling dynamics as a catalyst to create superlattices.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Stimuli‐Responsive Emission from Hybrid Metal Halides

Abstract Stimuli‐responsive photoluminescent (PL) materials have attracted considerable attention in recent years owing to their potential applications in anti‐counterfeiting, information encryption, and sensing. Further investigations of the transformation mechanism and potential applications of stimulus‐responsive PL materials are considerably important. In the current study, an organic–inorganic metal halide, C 9 H 15 N 3 SbCl 5 ([C 9 H 13 N 3 ] 2+ is a 1‐(2‐pyridyl) piperazine cation) is obtained, which exhibits a 0D structure withP‐1 space group. At room temperature, when excited by UV light, the C 9 H 15 N 3 SbCl 5 single crystals exhibit unimodal blue light emission at 405 nm, and grinding or hydrostatic pressure induces double‐peak emissions at 405 and 650 nm. Interestingly, double‐emission samples can be restored to single‐emission samples by short annealing or storage in air for 2 weeks, and this process is reversible. Luminescence response to mechanical stimuli can also be achieved in the presence of hydrochloric acid and water. Spectral analysis and the analysis of the microstructural changes revealed that the structural modifications of the inorganic group play a pivotal role in the response to the stimulus. Finally, a composite film device based on C 9 H 15 N 3 SbCl 5 is prepared to demonstrate the potential of these smart materials in anti‐counterfeiting and sensing applications.

Chemistry↗
DOE OSTI2023

Strain as a Global Factor in Stabilizing the Ferroelectric Properties of ZrO 2

Since the discovery of ferroelectricity in doped HfO 2 and ZrO 2 thin films over a decade ago, fluorite-structured ferroelectric thin films have attracted much research attention due to their excellent scalability and complementary metal-oxide semiconductor compatibility compared to conventional perovskite ferroelectric materials. Although various factors influencing the formation of the ferroelectric properties are identified, a clear understanding of the causes of the phase formation have been difficult to determine. In this work, ZrO 2 films deposited by atomic layer deposition and chemical solution deposition have resulted in films with completely different structural properties. Regardless of these differences, a general relationship between strain and phase formation is established, leading to a more unified understanding of ferroelectric phase formation in undoped ZrO 2 films, which can be applied to other fluorite-structured films.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Formation and Microwave Losses of Hydrides in Superconducting Niobium Thin Films Resulting from Fluoride Chemical Processing

Abstract Superconducting niobium (Nb) thin films have recently attracted significant attention due to their utility for quantum information technologies. In the processing of Nb thin films, fluoride‐based chemical etchants are commonly used to remove surface oxides that are known to affect superconducting quantum devices adversely. However, these same etchants can also introduce hydrogen to form Nb hydrides, potentially negatively impacting microwave loss performance. Here, comprehensive materials characterization of Nb hydrides formed in Nb thin films as a function of fluoride chemical treatments is presented. In particular, secondary‐ion mass spectrometry, X‐ray scattering, and transmission electron microscopy reveal the spatial distribution and phase transformation of Nb hydrides. The rate of hydride formation is determined by the fluoride solution acidity and the etch rate of Nb 2 O 5, which acts as a diffusion barrier for hydrogen into Nb. The resulting Nb hydrides are detrimental to Nb superconducting properties and lead to increased power‐independent microwave loss in coplanar waveguide resonators. However, Nb hydrides do not correlate with two‐level system loss or device aging mechanisms. Overall, this work provides insight into the formation of Nb hydrides and their role in microwave loss, thus guiding ongoing efforts to maximize coherence time in superconducting quantum devices.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Constructing Crown Ether-Based Supramolecular Adhesives with Ambient-Temperature Applicable and Durable Adhesion

Supramolecular adhesives are attracting considerable attentions owing to their dynamic and reversible bonding, while the complex curing conditions and poor performance under extreme conditions severely restrict their applicability. Herein, a series of tetra-crown ether-terminated polyethylene glycol (TCE-PEG) adhesives are presented in which plenty of supramolecular interactions, including Van der Waals, hydrogen bonding, π–π staking, metal coordination, and electrostatic ones, provide strong adhesion on multiple types of substrates. Highly relevant for practical applications, ultra-strong adhesivity of TCE-PEG can be achieved without requiring additional ultraviolet radiation, heat, or chemical treatment at ambient temperature. It also exhibits durable adhesive behavior, excellent underwater stability, and low-temperature tolerance. Especially, by incorporating ionic polymer fragments of polyethyleneimine hydrochloride, additional hydrogen bonding between secondary amines and crown ether rings can be induced to enhance the lap-shear strength to 7.21 MPa due to the formation of supramolecular cross-linked network. Finally, this work pioneers a rather unique supramolecular approach for easily formed, ultra-strong crown-ether-based adhesives bearing great potential for applications in critical environments of limited heat source and unallowed solvent usage.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Breaking Barriers in Chalcogenide Perovskite Synthesis: A Generalized Framework for Fabrication of BaMS 3 (M═Ti, Zr, Hf) Materials

Abstract Chalcogenide perovskites have garnered increasing attention as stable, non‐toxic alternatives to lead halide perovskites. However, their conventional synthesis at high temperatures (>1000 °C) has hindered widespread adoption. Recent studies have developed low‐to‐moderate temperature synthesis methods (<600 °C) using reactive precursors, yet a comprehensive understanding of the pivotal factors affecting reproducibility and repeatability remains elusive. This study delineates the critical factors in the low‐temperature synthesis of BaMS 3 (M═Zr, Hf, Ti) compounds and presents a generalized framework. Innovative approaches are developed for synthesizing BaMS 3 compounds using this framework involving organometallics for solution deposition. The molecular precursor routes, employing metal acetylacetonates to generate soluble metal–sulfur bonded complexes and metal–organic compounds to produce soluble metal‐thiolate, metal‐isothiocyanate, and metal‐trithiocarbonate species, are demonstrated to yield carbon‐free BaMS 3 . These methods have achieved the most contiguous films of BaZrS 3 and BaHfS 3 using solution deposition to date. Furthermore, a hybrid solution processing method involving stacking sputter‐deposited Zr and solution‐deposited BaS layers is employed to synthesize a contiguous, oxygen‐free BaZrS 3 film. The diffuse reflectance measurements indicate a direct bandgap of ≈ 1.85 eV for the BaZrS 3 films and ≈ 2.1 eV for the BaHfS 3 film under investigation.

25 ENERGY STORAGE↗
DOE OSTI2024

Research Progress and Perspectives on Pre‐Sodiation Strategies for Sodium‐Ion Batteries

Sodium‐ion batteries (SIBs) with abundant elements have garnered significant attention from researches as a promise compensation to lithium‐ion batteries (LIBs). However, the large‐scale commercial application of SIBs is partially hindered by the limited initial coulombic efficiency (ICE) due to the irreversible formation of solid electrolyte interphase (SEI) and intercalation into the defects in the anode. Similar to pre‐lithiation techniques, pre‐sodiation approaches are considered to be one of the most direct and effective way to compensate for the loss of active sodium at the anode side of SIBs during the initial cycle. In this context, additional sodium ions are pre‐injected to the cathode/anode material by chemical/electrochemical methods, aiming to improve battery span life and energy density. Here, this review delves into the necessity and impact of pre‐sodiation techniques, compiling the latest research progress, for instance, self‐sacrificing cathode additives, over‐sodiated cathode materials, direct contact and solution chemical pre‐sodiation. Notably, the research mechanisms underlying solution chemical pre‐sodiation are highlighted. This comprehensive overview aims to foster a deeper understanding of the pre‐sodiation techniques and expects to provide guidance for realizing the commercial application of high energy density sodium‐ion batteries.

25 ENERGY STORAGE↗