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At least 1,531 records · Page 85
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

K 2 CuX 3 (X = Cl, Br): All-Inorganic Lead-Free Blue Emitters with Near-Unity Photoluminescence Quantum Yield

Recently, copper(I) halides have been gaining increased attention as highly luminescent nontoxic alternatives to lead halide perovskites for optoelectronic applications. In this paper, we report preparation of blue emitting, lead free, all-inorganic halides K 2 CuX 3 (X = Cl, Br) through five synthetic methods including traditional solid-state and solution methods. The photoluminescence (PL) emission spectra of K 2 CuCl 3 and K 2 CuBr 3 exhibit narrow peaks centered at 392 and 388 nm with full widths at half-maximum (fwhm) values of ~54 nm. The visible bright blue emission is corroborated by the remarkably high photoluminescence quantum yield (PLQY) values up to ~97%. Furthermore, radioluminescence measurements on K 2 CuCl 3 yield a bright peak at 404 nm under irradiation with X-rays at 200 kVp and 20 mA, which is optimal for use with PMTs and Si photomultipliers, suggesting a strong potential of this family for radiation detection applications. Based on our combined experimental and computational investigations, the origin of the efficient luminescence in K 2 CuX 3 is attributed to the high stability self-trapped excitons (STE) formed in the one-dimensional anionic ∞ 1 [CuX 3 ] 2– chains. Advantageously, K 2 CuX 3 demonstrate improved air- and photostability compared to the previously reported copper(I) halides. The discovery of highly efficient and high stability light emitters based on earth-abundant copper(I) halides paves the way for their potential practical applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

“Unleaded” Perovskites: Status Quo and Future Prospects of Tin-Based Perovskite Solar Cells

The tremendous interest focused on organic–inorganic halide perovskites since 2012 derives from their unique optical and electrical properties, which make them excellent photovoltaic materials. Pb-based halide perovskite solar cells, in particular, currently stand at a record efficiency of ≈23%, fulfilling their potential toward commercialization. However, because of the toxicity concerns of Pb-based perovskite solar cells, their market prospects are hindered. In principle, Pb can be replaced with other less-toxic, environmentally benign metals. Sn-based perovskites are thus the far most promising alternative due to their very similar and perhaps even superior semiconductor characteristics. Additionally, after years of effort invested in Sn-based halide perovskites, sufficient breakthroughs have finally been achieved that make them the next runners up to the Pb halide perovskites. To help the reader better understand the nature of Sn-based halide perovskites, their optical and electrical properties are systematically discussed. Recent progress in Sn-based perovskite solar cells, focusing mainly on film fabrication methods and different device architectures, and highlighting roadblocks to progress and opportunities for future work are reviewed. Finally, a brief overview of mixed Sn/Pb-based systems with their anomalous yet beneficial optical trends are discussed. The current challenges and a future outlook for Sn-based perovskites are discussed.

14 SOLAR ENERGY↗
DOE OSTI2022

PbI 2 Nanocrystal Growth by Atomic Layer Deposition from Pb(tmhd) 2 and HI

Atomic layer deposition (ALD) allows for fine control over the thickness, stoichiometry, and structural defects of materials. ALD provides a suitable route to deposit lead halides, which can further be converted to perovskites for photovoltaics, photoemission, and photodetection, among other applications. Deposition of lead halides by ALD has already begun to be explored; however, the precursors used in published processes are highly hazardous, require expensive fabrication processes, or contain impurities that can jeopardize the optoelectronic properties of metal halide perovskites after conversion. In this work, we deposited lead iodide (PbI 2 ) by a facile ALD process involving only two readily accessible and low-cost precursors. PbI 2 nanocrystals were grown on soda-lime glass (SLG), silicon dioxide support grids, and silicon wafer substrates and provided the groundwork for further investigation into developing lead halide perovskite processes by ALD. Further, the ALD-grown PbI 2 was characterized by annular dark-field scanning transmission electron microscopy (ADF-STEM), atomic force microscopy (AFM), high resolution transmission electron microscopy (HRTEM), X-ray fluorescence (XRF), and X-ray photoemission spectroscopy (XPS), among other methods. This work presents the first step to synthesize lead halide perovskites with atomic control for applications such as interfacial layers in photovoltaics and for deposition in microcavities for lasing.

36 MATERIALS SCIENCE↗
DOE OSTI2019

EXAFS Spectroscopy of Fractional Mixed-Valence Charge Density Wave Systems

We present extended X-ray absorption fine structure (EXAFS) spectra and modeling of a series of structurally tunable quasi-one-dimensional mixed-valence platinum–halide linear chain materials, [Pt(en 2 )][Pt(en 2 )X 2 ](ClO 4 ) 4 with X = Cl, Br, I. The materials exhibit a commensurate charge density wave with fractional charge states on alternating platinum ions in the chain, as well as a Peierls distortion with alternating platinum–halide bond lengths. The amplitude of the charge density wave and, correspondingly, the extent of the Peierls distortion are controlled by the identity of the bridging halide ion. We have carried out ab initio multiple scattering calculations using the FEFF9 code to relate the oriented Pt L III EXAFS spectra to the tunable electronic and structural properties. The spectral modeling reveals distinct photoelectron threshold energy values for the two inequivalent platinum ions in each of the mixed-valence chains, with values that vary systematically with fractional valence state. The difference in the photoelectron threshold energies of the two inequivalent platinum ions within each material correlates directly with the amplitude of the charge density wave, reflecting the decrease in charge density wave strength through the halide series X = Cl, Br, and I. We use dynamical matrix modeling to relate the experimentally determined mean-square relative displacement parameters for the metal–halide bond distances to the chain–axis vibrational modes that modulate the charge density wave structure. In addition, we discuss the EXAFS fitting results for the Pt–I bond lengths in the [Pt(en 2 )][Pt(en 2 )I 2 ](ClO 4 ) 4 complex in comparison to previous, mutually inconsistent structural determinations for this material.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Compositional Engineering for Efficient Wide Band Gap Perovskites with Improved Stability to Photoinduced Phase Segregation

Metal halide perovskites are attractive candidates for the wide band gap absorber in tandem solar cells. While their band gap can be tuned by partial halide substitution, mixed halide perovskites often have lower open-circuit voltage than would be expected and experience photoinduced trap formation caused by halide segregation. Here, we investigate solar cell performance and photostability across a compositional space of formamidinium (FA) and cesium (Cs) at the A-site at various halide compositions and show that using more Cs at the A-site rather than more Br at the X-site to raise band gap is more ideal as it improves both VOC and photostability. We develop band gap maps and design criteria for the selection of perovskite compositions within the Cs x FA 1–x Pb(Br y I 1–y ) 3 , space. With this, we identify perovskites with tandem-relevant band gaps of 1.68 and 1.75 eV that demonstrate high device efficiencies of 17.4 and 16.3%, respectively, and significantly improved photostability compared to that of the higher Br-containing compositions.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Evidence for halogen bond covalency in acyclic and interlocked halogen-bonding receptor anion recognition

The synthesis and anion binding properties of novel halogen-bonding (XB) bis-iodotriazole-pyridinium-containing acyclic and [2]catenane anion host systems are described. The XB acyclic receptor displays selectivity for acetate over halides with enhanced anion recognition properties compared to the analogous hydrogen-bonding (HB) acyclic receptor. A reversal in halide selectivity is observed in the XB [2]catenane, in comparison to the acyclic XB receptor, due to the interlocked host’s unique three-dimensional binding cavity, and no binding is observed for oxoanions. Notable halide anion association constant values determined for the [2]catenane in competitive organic–aqueous solvent mixtures demonstrate considerable enhancement of anion recognition as compared to the HB catenane analogue. X-ray crystallographic analysis of a series of halide catenane complexes reveal strong XB interactions in the solid state. These interactions were studied using Cl and Br K-edge X-ray Absorption Spectroscopy (XAS) indicating intense pre-edge features characteristic of charge transfer from the halide to its bonding partner (σ AX←X– * ← X1s), and providing a direct measure of the degree of covalency in the halogen bond(s). Lastly, the data reveal that the degree of covalency is similar to that which is observed in transition metal coordinate covalent bonds. These results are supported by DFT results, which correlate well with the experimental data.

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

Design of High-Performance Lead-Free Quaternary Antiperovskites for Photovoltaics via Ion Type Inversion and Anion Ordering

The emergence of halide double perovskites significantly increases the compositional space for lead-free and air-stable photovoltaic absorbers compared to halide perovskites. Nevertheless, most halide double perovskites exhibit oversized band gaps (>1.9 eV) or dipole-forbidden optical transition, which are unfavorable for efficient single-junction solar cell applications. The current device performance of halide double perovskite is still inferior to that of lead-based halide perovskites, such as CH 3 NH 3 PbI 3 (MAPbI 3 ). Here, by ion type inversion and anion ordering on perovskite lattice sites, two new classes of pnictogen-based quaternary antiperovskites with the formula of X 6 B 2 AA' and X 6 BB'A 2 are designed. Phase stability and tunable band gaps in these quaternary antiperovskites are demonstrated based on first-principles calculations. Further photovoltaic-functionality-directed screening of these materials leads to the discovery of 5 stable compounds (Ca 6 N 2 AsSb, Ca 6 N 2 PSb, Sr 6 N 2 AsSb, Sr 6 N 2 PSb, and Ca 6 NPSb 2 ) with suitable direct band gaps, small carrier effective masses and low exciton binding energies, and dipole-allowed strong optical absorption, which are favorable properties for a photovoltaic absorber material. The calculated theoretical maximum solar cell efficiencies based on these five compounds are all larger than 29%, comparable to or even higher than that of the MAPbI 3 based solar cell. Finally, our work reveals the huge potential of quaternary antiperovskites in the optoelectronic field and provides a new strategy to design lead-free and air-stable perovskite-based photovoltaic absorber materials.

three-dimensional electronic transport↗
DOE OSTI2021

Halogenation of used aluminum matrix test reactor fuel – a bench-scale demonstration with surrogate materials

In this work, experiments with surrogate materials were performed at bench scale to demonstrate a halogenation technique applicable to treatment of used aluminum matrix test reactor fuel. The technique involves dissolution and separation of aluminum from used aluminum matrix test reactor fuel in molten-halide salt systems prior to treatment and disposition of the fuel’s uranium and fission products. Demonstration of the halogenation technique was performed with neodymium metal as a non-radiological surrogate for uranium metal. Experiments involved blending forms of aluminum and neodymium metal with ammonium and lithium chloride or ammonium and lithium bromide, which upon heating decomposed into ammonia gas and the respective hydrogen chloride or bromide gas. The latter reacted with the metals to form the respective aluminum and neodymium halides. At elevated temperatures, aluminum halides gasified away from the respective neodymium halides, which fused with their respective lithium halides. Samples of fused and distillate salts were collected and analyzed, yielding extents of aluminum removal that ranged from 94.5–98.2% for chlorination runs and 91.4–97.8% for bromination runs. No neodymium was detected in the distillate fractions. Some experiments were repeated with excess reactants, and a portion of aluminum chloride distillate was processed into a consolidated waste form.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

High Performance Perovskite-Based Solar Cells (Final Technical Report)

Hybrid lead-halide perovskite semiconductors have become one of the most heavily studied photovoltaic (PV) materials within the past ten years. However, these materials suffer from two key limitations that have ultimately limited the progression towards commercialization: (i) the inclusion of toxic lead (Pb) and (ii) instability towards moisture, oxygen, and temperature. This project has targeted the development of perovskite absorber materials that replace Pb with a benign alternative and that are stable under atmospheric conditions. Under this broad goal, the project had four major objectives: 1) Develop high-performance Pb-based PV devices and study alternative inorganic contact materials to improve the device stability; 2) Advance computational techniques to understand the electronic and optical properties of perovskite semiconductors from a theoretical perspective; 3) Explore various hybrid and inorganic halide, chalcohalide and chalcogenide perovskite absorbers as highly stable, Pb-free absorber alternatives; 4) Develop thin-film deposition and device fabrication methodologies to deposit high-quality Pb-free perovskite absorbers and high-performance devices. Within the first objective, the researchers fabricated high-performing methylammonium lead iodide solar cells based on both traditional architectures (using a TiO 2 contact) and inverted architectures using NiOx and novel CuCrO 2 as hole transport layers (HTL). The work with CuCrO 2 is the first work demonstrating CuCrO 2 as a promising contact material for future, stable perovskite solar cells. Towards the second objective researchers have calculated the intrinsic stability and optoelectronic properties of multiple Pb-free systems including chalcohalide (e.g. CsBiOF 2 ), halide (e.g. Cs 3 Sb 2 I 9 ), and chalcogenide perovskites (e.g. BaZr 1-x TixS 3 ). Additionally, the researchers have furthered the basic understanding of perovskite materials by introducing the concept of electronic dimensionality and its impact on optoelectronic properties. This understanding has had implications in PV applications and beyond. In the third and fourth objectives, the investigators have exhausted a myriad of Pb-free materials in search of a stable, promising Pb-free perovskite absorber, including chalochalides based on CsBiOF 2 , Pb-free halides (such as Cs 2 AgBiBr 6 , Cs 2 TiBr 6 , and Cs(Ge/Sn)I 3 ) , chalcogenide perovskites (e.g. BaZrS 3 ), and perovskite-related halides InI and silver bismuth iodide. While the researchers have studied many promising perovskites and perovskite-alternatives, a stable, high-performing Pb-free absorber has proven to be elusive.

14 SOLAR ENERGY↗
NASA NTRS1993

Global expression for representing cohesive-energy curves. II

Schlosser et al. (1991) showed that the R dependence of the cohesive energy of partially ionic solids may be characterized by a two-term energy relationship consisting of a Coulomb term arising from the charge transfer, delta-Z, and a scaled universal energy function, E*(a *), which accounts for the partially covalent character of the bond and for repulsion between the atomic cores for small R; a* is a scaled length. In the paper by Schlosser et al., the normalized cohesive-energy curves of NaCl-structure alkali-halide crystals were generated with this expression. In this paper we generate the cohesive-energy curves of several families of partially ionic solids with different crystal structures and differing degrees of ionicity. These include the CsCl-structure Cs halides, and the Tl and Ag halides, which have weaker ionic bonding than the alkali halides, and which have the CsCl and NaCl structures, respectively. The cohesive-energy-curve parameters are then used to generate theoretical isothermal compression curves for the Li, Na, K, Cs, and Ag halides. We find good agreement with the available experimental compression data.

Schlosser, Herbert↗
DOE OSTI2015

Methods for improved growth of group III nitride semiconductor compounds

Methods are disclosed for growing group III-nitride semiconductor compounds with advanced buffer layer technique. In an embodiment, a method includes providing a suitable substrate in a processing chamber of a hydride vapor phase epitaxy processing system. The method includes forming an AlN buffer layer by flowing an ammonia gas into a growth zone of the processing chamber, flowing an aluminum halide containing precursor to the growth zone and at the same time flowing additional hydrogen halide or halogen gas into the growth zone of the processing chamber. The additional hydrogen halide or halogen gas that is flowed into the growth zone during buffer layer deposition suppresses homogeneous AlN particle formation. The hydrogen halide or halogen gas may continue flowing for a time period while the flow of the aluminum halide containing precursor is turned off.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Dendrite inhibiting electrolytes for metal-based batteries

A metal-based battery includes at least one metal electrode immersed within an electrolyte that includes: (1) an aprotic solvent; (2) a simple halogen containing material; and (3) optionally a metal salt that includes a complex halogen containing anion. The simple halogen containing material may include a metal halide salt that includes a metal cation selected from the group including but not limited to lithium and sodium metal cations. The metal halide salt may also include a halide anion selected from the group consisting of fluoride, chloride, bromide and iodide halide anions. The use of the metal halide salt within the metal-based battery provides enhanced cycling ability within the metal-based battery. Also contemplated are additional simple halogen containing material additives that may enhance cycling performance of a metal-based battery.

Archer, Lynden A.↗
DOE OSTI2021

Molten salt compositions with enhanced heat transfer and reduced corrosion properties

A heat transfer (exchange) composition comprising a halide salt matrix having dispersed therein nanoparticles comprising elemental carbon in the absence of water and surfactants, wherein said halide is fluoride or chloride, wherein the halide salt may be an alkali halide salt (e.g., lithium fluoride, sodium fluoride, potassium fluoride, rubidium fluoride, sodium chloride, potassium chloride, rubidium chloride, and eutectic mixtures thereof) or an alkaline earth halide salt (e.g., fluoride or chloride salt of beryllium, magnesium, calcium, strontium, or barium), and wherein the nanoparticles comprising elemental carbon may be solid or hollow, and wherein the composition may further include nanoparticles comprising a fissile material (e.g., U, Th, or Pu) dispersed within the composition. Molten salt reactors (MSRs) containing these heat transfer compositions in coolant loops in thermal exchange with a reactor core, as well operation of such MSRs, are also described.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2021

Methods for electropolishing and coating aluminum on air and/or moisture sensitive substrates

Methods for electropolishing and coating aluminum on a surface of an air and/or moisture sensitive substrate, including: in a vessel, submerging the substrate in a first molten salt bath and applying an anodizing current to the substrate at a first temperature to electropolish the surface of the substrate; wherein the first molten salt bath includes one of a first organic salt bath and first inorganic salt bath; wherein, when used, the first organic salt bath includes one of (a) aluminum halide and ionic liquid, (b) a combination of an aluminum halide and halogenatedmethylphenylsulfone (C 6 (H 5−y ,X y )SO 2 CX 3 , where y is a number from 0-5), (c) a combination of an aluminum halide, an ionic liquid, and halogenatedmethylphenylsulfone (C 6 (H 5−y ,X y )SO 2 CX 3 ), and (d) AlF 3 -organofluoride-hydrofluoric acid adduct; wherein, when used, the first inorganic salt bath includes aluminum halide and alkali metal halide; and wherein the anodizing current is 10-30 mA/cm 2 .

Freiderich, John W.↗
DOE OSTI2022

Methods for electropolishing and coating aluminum on air and/or moisture sensitive substrates

Methods for electropolishing and coating aluminum on a surface of an air and/or moisture sensitive substrate, including: in a vessel, submerging the substrate in a first molten salt bath and applying an anodizing current to the substrate at a first temperature to electropolish the surface of the substrate; wherein the first molten salt bath includes one of a first organic salt bath and first inorganic salt bath; wherein, when used, the first organic salt bath includes one of (a) aluminum halide and ionic liquid, (b) a combination of an aluminum halide and halogenatedmethylphenylsulfone (C 6 (H 5-y ,X y )SO 2 CX 3 , where y is a number from 0-5), (c) a combination of an aluminum halide, an ionic liquid, and halogenatedmethylphenylsulfone (C 6 (H 5-y ,X y )SO 2 CX 3 ), and (d) AlF 3 -organofluoride-hydrofluoric acid adduct; wherein, when used, the first inorganic salt bath includes aluminum halide and alkali metal halide; and wherein the anodizing current is 10-30 mA/cm 2 .

Freiderich, John W.↗
DOE OSTI2023

Methods of forming a metal coated article

A method of forming a metal coated article, comprises forming a metal halide in a molten salt plating bath at a first temperature, wherein forming the metal halide in the molten salt further comprises forming at least one functional metal halide electrolyte; and forming at least two auxiliary metal halide electrolytes at eutectic conditions; increasing the first temperature to a second temperature; forming a plated metal coating from the at least one functional metal halide electrolyte onto a thermally conductive substrate; and introducing at least one of deuterium and tritium into the plated metal coating.

Tripathy, Prabhat K.↗
DOE OSTI2024

Synthetic Control of Water-Stable Hybrid Perovskitoid Semiconductors

Hybrid metal-halide perovskites and their derived materials have emerged as the next-generation semiconductors with a wide range of applications, including photovoltaics, light-emitting devices, and other optoelectronics. Over the past decade, numerous single-crystalline perovskite derivatives have been synthesized and developed. However, the synthetic methods for these derivatives mainly rely on acidic crystallization conditions. This approach leads to crystals comprising metal halide building blocks, which show problematic stability when directly exposed to water. In this study, a methodology is developed for synthesizing hybrid metal-halide compounds using lead iodide and the zwitterionic bifunctional molecule cysteamine (CYS), to form various perovskitoid structures under a broad pH range. Interestingly, the different pH conditions alter the coordination environment of lead halides, leading to lead-sulfide and lead-nitride covalent bond formation. This modification significantly enhances their stability when in direct contact with water, lasting for months. Photoluminescence measurements and first principal density functional theory (DFT) calculations reveal that the perovskitoids synthesized under basic and acidic pH conditions exhibit a direct bandgap nature, while those synthesized under neutral conditions display an indirect bandgap. This approach opens new avenues for manipulating synthetic methods to develop water-stable hybrid semiconductors suitable for a wide range of applications, such as solid-state light emitters.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Temperature and anion ligand field dependence of LnCl 3 (Ln = Nd, Dy, Sm) electronic absorption spectra in LiCl–KCl eutectic molten salt

A comprehensive knowledge of the coordination, bonding, and speciation of elements in molten salt mixtures is necessary to understand and predict the chemical and physical properties of the salt. Absorption spectroscopy can yield information about the chemistry of species of interest in alkali halide molten salt mixtures by revealing information about the electronic structure and transitions of those species. In this study, ultraviolet (UV), visible (vis), and near-infrared (NIR) absorption spectroscopy was used to examine changes to the electronic structure of trivalent Nd, Sm, and Dy in LiCl–KCl eutectic molten salt with changes in temperature and the anion composition of the melt. With increasing temperature, changes to spectral features suggest a distortion of the coordination complexes. Changes to lineshape with the substitution of alternative halide anions were examined and analyzed, revealing differences in the coordination for I – versus F – with the lanthanides. Gaussian peak fitting was used to show that the changes in lineshape with the progressive addition of F – anions can be explained by the superposition of a set of absorption bands from complexes with all Cl – anion ligands and a set of blueshifted absorption bands from complexes containing both F – and Cl – anion ligands. Finally, this work yields a new method to analyze and interpret change to electronic absorption spectra for f-block elements dissolved in alkali halide molten salts as well as new observations of the interactions of larger and smaller halide anions with lanthanides in Cl – -based molten salts.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗