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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Chalcogen effect on the photovoltaic performance of nonfused-ring small molecular electron acceptors for efficient organic solar cells

Fused-ring electron acceptors (FREAs) are the current working horse for the top performing organic solar cells (OSCs). Nevertheless, these FREAs surfer from high synthetic complexity, production costs and poor scalability, hindering their industrialization. Developing nonfused-ring electron acceptors (NFREAs) is a more feasible alternative solution towards future photovoltaic applications. Here, in this work, a series of NFREAs have been designed and synthesized by introducing chalcogen atoms on the side chains for OSCs. The introduced chalcogen atoms (O, S, and Se) not only modulated the energy levels but also finely tuned the intermolecular interactions. Especially, the formed S···S and Se···Se intermolecular interactions in TTS-4F and TTSe-4F resulted in higher molecular crystallinity than TTO-4F. Unexpectedly, the strong Se···Se interactions also led the aggregation of TTSe-4F and formation of large domains in the PM6:TTSe-4F blend. The moderate S···S interactions in TTS-4F enabled an optimal phase separation with more ideal nano fibrils distributed in the PM6:TTS-4F blend, facilitating the charge separation and transport. As a result, TTS-4F based devices achieved a champion power conversion efficiency (PCE) of 14.74%, higher than the TTO-4F (8.76%) and TTSe-4F (11.56%) based devices.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Unequal {110} Facets: The Potential Role of Intraparticle Heterogeneity and Facet Termination in Photoelectrochemical Activity of Single BiVO 4 Particles

BiVO 4 photoanodes are promising for solar water splitting, with photogenerated electrons and holes preferentially reacting at top {010} and lateral {110} facets, respectively. However, the mechanisms driving this facet-dependent reactivity remain unclear. Here, in this study, we investigate facet-dependent photocurrent and material heterogeneity using correlative scanning photoelectrochemical microscopy (SPCM), electron beam induced current (EBIC) mapping, and mid-IR scattering scanning near-field optical microscopy (s-SNOM). SPCM measurements of 62 BiVO 4 particles confirmed higher photocurrents at lateral {110} facets compared to top {010} facets, but unexpectedly revealed variations in photocurrent among lateral facets within the same particle. Variations in lateral facet surface termination could explain the intraparticle-level reactivity heterogeneity, consistent with theoretical predictions. Nano-FTIR spectroscopy and Raman microspectroscopy indicated significant materials chemistry heterogeneity within individual particles and facets that could be attributed to variations in lattice vibration distortions that enhance the overlap between Bi 6s and O 2p orbitals. The increased orbital overlap is significant as it potentially increases hole mobility in the valence band and potentially explains the lateral facet-dependent charge separation efficiency observed in photocurrent maps. Facet-dependent electrical and EBIC measurements showed no space charge regions at interfacet junctions or metal-BiVO 4 contacts under vacuum, suggesting that photogenerated holes beneath top {010} facets are unlikely to transport to lateral {110} facets to drive water/sulfite oxidation. These findings indicate the potential influence of distinct bulk properties and surface termination chemistries across different particles and facets, highlighting the importance of carefully controlling defects and surface chemistry during sample growth to optimize photocatalytic performance.

BiVO4↗
DOE OSTI2025

Chemical Interface Damping Revealed by Single-Particle Absorption Spectroscopy

Plasmon-induced interfacial charge separation is a promising way to efficiently extract energetic carriers through direct plasmon decay. This mechanism of charge transfer has been investigated by single-particle scattering spectroscopy, which measures the homogeneous plasmon line width. The line width is broadened by charge transfer, generally known as chemical interface damping. However, conflicting reports exist regarding the effect of chemical interface damping on the corresponding single-particle absorption spectrum, which is needed to accurately determine absolute light conversion efficiencies. This work aims to resolve this question by directly correlating absorption and scattering spectra of individual gold nanorods in the presence and absence of a charge-accepting interface. We find that for TiO 2 coated nanorods, the absorption line width is indeed broadened due to chemical interface damping but is overall narrower than the scattering line width. Here, chemical interface damping is furthermore found to increase with larger resonance energies. The observed differences in line widths between absorption and scattering are elucidated within the context of an analytically tractable model describing the lowest energy optically bright and higher-order optically dark plasmon modes of the nanorod, including bulk, radiative, and chemical interface damping effects. Taken together, these results establish that single-particle absorption spectroscopy is capable of revealing interfacial charge injection by direct plasmon decay.

absorption↗
DOE OSTI2025

Vibronic coupling-driven symmetry breaking and solvation in the photoexcited dynamics of quadrupolar dyes

Quadrupolar dyes, such as acceptor–donor–acceptor molecules, are highly relevant for applications in nonlinear optics and photovoltaics. They are also versatile models for exploring photoinduced charge-transfer dynamics. The interplay between electronic and vibronic couplings in these molecules may break excited-state symmetry, resulting in intramolecular charge separation and pronounced solvatochromism. Experimentally, distinguishing the roles of intramolecular vibronic coupling and solvent reorganization for the initial charge-transfer dynamics has been challenging so far. Here we investigate a prototypical quadrupolar dye in polar and non-polar solvents using ultrafast pump–probe and two-dimensional electronic spectroscopy. Our results reveal that vibronic couplings initiate excited-state symmetry breaking during the first ~50 fs of the photoinduced charge transfer, whereas solvent-induced charge localization sets in at later times. Quantum dynamics and electronic structure simulations support our experimental findings. Our results reveal the details of solvation dynamics in photoexcited molecules and suggest strategies for their manipulation through vibronic couplings.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Bidentate Lewis bases are preferred for passivation of MAPbI 3 surfaces: A time-domain ab initio analysis

We report chemical passivation is a predominant approach to inhibit intrinsic defects responsible for electron–hole recombination in perovskite solar cells. Using time-domain density functional theory combined with nonadiabatic molecular dynamics, we demonstrate defect passivation by separation of electrons and holes in metal halide perovskites (MHPs), and show that bidentate ligands exhibit the best performance. Defects in traditional semiconductors create deep midgap states, and passivation eliminates these states. In contrast, common defects produce no deep midgap states in MHPs. Instead, defects localize electrons and holes around defect sites, enhancing electron–hole interaction. Defect passivation in MHPs acts to separate charges, decreasing electron–hole and charge–phonon interactions, and increasing charge lifetimes. Bidentate ligands work best, because they can passivate both unsaturated chemical bonds created due to vacancy defects. Bidentate ligands with spatially separated binding sites are preferred, since they provide better match to the sparse inorganic lattice of MHPs. Similar to the Lewis base ligands, water also acts as a ligand and extends charge lifetimes, with the oxygen atom donating its lone electron pair to the defect site. However, water accelerates chemical degradation of MHPs. The binding energy of most ligands is larger than that of water, and therefore, the ligands displace water, increase MHP stability and prolong carrier lifetimes. The established physical mechanism of defect passivation, and the specific principles guiding the choice of passivating molecules advance our understanding of the exceptional properties of MHPs and suggest routes for further improvement of MHP performance in solar energy and optoelectronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Comprehensive Evaluation for Protective Coatings: Optical, Electrical, Photoelectrochemical, and Spectroscopic Characterizations

Numerous efficient semiconductors suffer from instability in aqueous electrolytes. Strategies utilizing protective coatings have thus been developed to protect these photoabsorbers against corrosion while synergistically improving charge separation and reaction kinetics. Recently, various photoelectrochemical (PEC) protective coatings have been reported with suitable electronic properties to ensure low charge transport loss and reveal the fundamental photoabsorber efficiency. However, protocols for studying the critical figures of merit for protective coatings have yet to be established. For this reason, we propose four criteria for evaluating the performance of a protective coating for PEC water-splitting: stability, conductivity, optical transparency, and energetic matching. We then propose a flow chart that summarizes the recommended testing protocols for quantifying these four performance metrics. In particular, we lay out the stepwise testing protocols to evaluate the energetics matching at a semiconductor/coating/(catalyst)/liquid interface. Finally, we provide an outlook for the future benchmarking needs for coatings.

36 MATERIALS SCIENCE↗
NASA NTRS1973

Energy spectrum and flux of 3- to 20-Mev neutrons and 1- to 10-Mev gamma rays in the atmosphere

An experiment is described which was designed to measure the neutron and gamma ray energy spectrums and fluxes in the energy intervals 3 to 20 MeV and 1 to 10 MeV, respectively. In addition, from the 3 to 20-MeV proton recoil spectrums it is possible to infer the shape of the neutron energy spectrum from 20 to 50 MeV. The detecting system utilized a separate charged particle rejection scheme and a two-parameter display system for the output from the pulse shape discrimination which separated gamma rays from neutrons (n). Two long-duration flights were made with this detector in 1970 at Palestine, Tex. (P sub c = 4.6 Gv) and at Ft. Churchill, Canada (P sub c = 0.3 Gv).

Klumpar, D. M.↗
DOE OSTI2022

A charge transfer framework that describes supramolecular interactions governing structure and properties of 2D perovskites

The elucidation of structure-to-function relationships for two-dimensional (2D) hybrid perovskites remains a primary challenge for engineering efficient perovskite-based devices. By combining insights from theory and experiment, we describe the introduction of bifunctional ligands that are capable of making strong hydrogen bonds within the organic bilayer. We find that stronger intermolecular interactions draw charge away from the perovskite layers, and we have formulated a simple and intuitive computational descriptor, the charge separation descriptor (CSD), that accurately describes the relationship between the Pb-I-Pb angle, band gap, and in-plane charge transport with the strength of these interactions. A higher CSD value correlates to less distortion of the Pb-I-Pb angle, a reduced band gap, and higher in-plane mobility of the perovskite. These improved material properties result in improved device characteristics of the resulting solar cells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Dynamic Competition between Hubbard and Superexchange Interactions Selectively Localizes Electrons and Holes through Polarons

Controlling the effects of photoexcited polarons in transition metal oxides can enable the long time-scale charge separation necessary for renewable energy applications and controlling new quantum phases through dynamically tunable electron–phonon coupling. In previously studied transition metal oxides, polaron formation is facilitated by a photoexcited ligand-to-metal charge transfer (LMCT). When the polaron is formed, oxygen atoms move away from iron centers, which increases carrier localization at the metal center and decreases charge hopping. Studies of yttrium iron garnet and erbium iron oxide have suggested that strong electron and spin correlations can modulate photoexcited polaron formation. To understand the interplay between strong spin and electronic correlations in highly polar materials, we studied gadolinium iron oxide (GdFeO 3 ), which selectively forms photoexcited polarons through an Fe–O–Fe superexchange interaction. Excitation-wavelength-dependent transient extreme ultraviolet (XUV) spectroscopy selectively excites LMCT and metal-to-metal charge transfer (MMCT) transitions. Here, the LMCT transition suppresses photoexcited polaron formation due to the balance between superexchange and Hubbard interactions, while MMCT transitions result in photoexcited polaron formation within 250 ± 40 fs. Ab initio theory demonstrates that electron and hole polarons localize on iron centers following MMCT. In addition to understanding how strong electronic and spin correlations can control strong electron–phonon coupling, these experiments separately measure electron and hole polaron interactions on neighboring metal centers for the first time, providing insight into a large range of charge-transfer and Mott–Hubbard insulators.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

ArCS: A Magnetized LArTPC in a Test Beam

Over the past few decades, Liquid Argon Time Projection Chambers (LArTPCs) have emerged as a central technology for rare-event detection, due to their calorimetric and imaging capabilities. Adding a magnetic field to LArTPCs would enable charge identification and momentum measurements via curvature. For neutrino experiments, this is crucial for wrong-sign neutrino rejection, electron/positron and electron/photon discrimination, and improved momentum reconstruction. The ArCS (Argon detector with Charge Separation) experiment at Fermilab's Test Beam Facility will place a 47 40 90 cm LArTPC inside a 0.7 T magnet to: (i) establish charge sign discrimination for electrons and positrons, (ii) reconstruct particle momenta via curvature, and (iii) determine the minimal magnetic field needed for these measurements. This poster will present the project status, with updates on installation and simulations of expected performance.

Cicogna, Giulia [Bologna U.]↗
DOE OSTI2023

Changing Directions: Influence of Ligand Electronics on the Directionality and Kinetics of Photoinduced Charge Transfer in Cu(I)Diimine Complexes

A key challenge to the effective utilization of solar energy is to promote efficient photoinduced charge transfer, specifically avoiding unproductive, circuitous electron-transfer pathways and optimizing the kinetics of charge separation and recombination. We hypothesize that one way to address this challenge is to develop a fundamental understanding of how to initiate and control directional photoinduced charge transfer, particularly for earth-abundant first-row transition-metal coordination complexes, which typically suffer from relatively short excited-state lifetimes. Here, in this paper, we report a series of functionalized heteroleptic copper(I)bis(phenanthroline) complexes, which have allowed us to investigate the directionality of intramolecular photoinduced metal-to-ligand charge transfer (MLCT) as a function of the substituent Hammett parameter. Ultrafast transient absorption suggests a complicated interplay of MLCT localization and solvent interaction with the Cu(II) center of the MLCT state. This work provides a set of design principles for directional charge transfer in earth-abundant complexes and can be used to efficiently design pathways for connecting the molecular modules to catalysts or electrodes and integration into systems for light-driven catalysis.

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

Diverse simulations of time-resolved photoluminescence in thin-film solar cells: A SnO 2 /CdSe y Te 1-y case study

Time-resolved photoluminescence (TRPL) is widely used to measure carrier lifetime in thin-film solar cell absorbers. However, the injection dependence of data and frequent non-exponential decay shapes complicate the interpretation. Here, we develop a numerical model to simulate injection-dependent TRPL measurements in a SnO 2 /CdSe y Te 1-y case study solar cell structure, considering parameters of interest to researchers in industry and academia. Previous simulations have shown that, in low injection, excess electrons and holes injected by the laser pulse are rapidly separated in the electric field formed by the pn junction. As a result, at early times, the PL signal can decay faster than the Shockley-Read-Hall lifetime in the absorber bulk (t_bulk). Prior simulations have shown that the charge stored in the junction can slowly leak out to affect decays at late times. However, it has not been clear if and to what degree charge storage can affect the slopes extracted from TRPL decays - t_2 - commonly cited as the TRPL-measured lifetime. Here, we show that charge storage can, in some cases, result in t_2 values that substantially overestimate t_bulk. Previous simulations indicate that high injection conditions can screen the junction field and minimize charge separation. Here, we show that continued injection increases can drive down t_2 below t_bulk as radiative recombination becomes dominant. We catalog charge storage and radiative recombination impacts for a diverse set of material parameters and compare results to double-heterostructure models.

CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS,S↗
NASA NTRS1983

Lightning generation in planetary atmospheres

The possibilities of lightning generation on other planets are considered, and the basic conditions that exist in terrestrial clouds during lightning discharges and the various theories of charge separation are reviewed. The properties of terrestrial clouds that produce lightning, the properties of lightning itself, and the fairweather field are first reviewed. The general requirements and the different proposed charging mechanisms for electrification of terrestrial clouds are discussed. The mechanisms of electrical breakdown and whistler production are considered, and recent observations of extraterrestrial lightning and of clouds on other planetary bodies are summarized. Circumstances likely to account for lightning activity on Jupiter and Venus and for electrical activity on Mars and in the rings of Saturn are discussed.

Borucki, W. J.↗
DOE OSTI2023

Ti‐Modified Imogolite Nanotubes as Promising Photocatalyst 1D Nanostructures for H 2 Production

Imogolite nanotubes (INTs) are predicted as a unique 1D material with spatial separation of conduction and valence band edges but their large band gaps have inhibited their use as photocatalysts. The first step toward using these NTs in photocatalysis and exploiting the polarization-promoted charge separation across their walls is to reduce their band gap. Here, the modification of double-walled aluminogermanate INTs by incorporation of titanium into the NT walls is explored. The precursor ratio x = [Ti]/([Ge]+[Ti]) is modulated between 0 and 1. Structural and optical properties are determined at different scales and the photocatalytic performance is evaluated for H 2 production. Although the incorporation of Ti atoms into the structure remains limited, the optimal condition is found around x = 0.4 for which the resulting NTs reveal a remarkable hydrogen production of ≈1500 µmol g −1 after 5 h for a noble metal-free photocatalyst, a 65-fold increase relative to a commercial TiO 2 -P25. This is correlated to a lowering of the recombination rate of photogenerated charge carriers for the most active structures. These results confirm the theoretical predictions regarding the potential of modified INTs as photoactive nanoreactors and pave the way for investigating and exploiting their polarization properties for energy applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1986

Electric field measurements during the Condor critical velocity experiment

The instrumentation of the Condor critical velocity Ba experiment (Wescott et al., 1986) for the measurements of the energetic particles and the electric field associated with a Ba explosion is described. The Ba explosion created a complex electric field pulse detected in situ by a single-axis double electric-field probe on a separate spacecraft. The measurements provide evidence of several important links in the critical-velocity chain, and are consistent with two hypotheses. The first hypothesis involves the creation of large polarization electric field due to charge separation; the second hypothesis implies a polarization of the beam by currents flowing across it. The chain of physical processes inferred from the observations is in agreement with most theories for the Alfven process.

Kelley, M. C.↗
NASA NTRS2013

Li-Ion Battery and Supercapacitor Hybrid Design for Long Extravehicular Activities

With the need for long periods of extravehicular activities (EVAs) on the Moon or Mars or a near-asteroid, the need for long-performance batteries has increased significantly. The energy requirements for the EVA suit, as well as surface systems such as rovers, have increased significantly due to the number of applications they need to power at the same time. However, even with the best state-of-the-art Li-ion batteries, it is not possible to power the suit or the rovers for the extended period of performance. Carrying a charging system along with the batteries makes it cumbersome and requires a self-contained power source for the charging system that is usually not possible. An innovative method to charge and use the Li-ion batteries for long periods seems to be necessary and hence, with the advent of the Li-ion supercapacitors, a method has been developed to extend the performance period of the Li-ion power system for future exploration applications. The Li-ion supercapacitors have a working voltage range of 3.8 to 2.5 V, and are different from a traditional supercapacitor that typically has a working voltage of 1 V. The innovation is to use this Li-ion supercapacitor to charge Liion battery systems on an as-needed basis. The supercapacitors are charged using solar arrays and have battery systems of low capacity in parallel to be able to charge any one battery system while they provide power to the application. Supercapacitors can safely take up fast charge since the electrochemical process involved is still based on charge separation rather than the intercalation process seen in Li-ion batteries, thus preventing lithium metal deposition on the anodes. The lack of intercalation and eliminating wear of the supercapacitors allows for them to be charged and discharged safely for a few tens of thousands of cycles. The Li-ion supercapacitors can be charged from the solar cells during the day during an extended EVA. The Liion battery used can be half the capacity required for a nominal EVA. The small Li-ion battery can be divided into two parallel modules with independent charging ports that would allow the supercapacitors to charge one battery while the other is providing power to the rover or suit.

Jeevarajan, Judith↗
DOE OSTI2023

Type-I CdS/ZnS Core/Shell Quantum Dot-Gold Heterostructural Nanocrystals for Enhanced Photocatalytic Hydrogen Generation

Developing Type-I core/shell quantum dots is of great importance toward fabricating stable and sustainable photocatalysts. However, the application of Type-I systems has been limited due to the strongly confined photogenerated charges by the energy barrier originating from the wide-bandgap shell material. In this project, we found that through the decoration of Au satellite-type domains on the surface of Type-I CdS/ZnS core/shell quantum dots, such an energy barrier can be effectively overcome and an over 400-fold enhancement of photocatalytic H(2) evolution rate was achieved compared to bare CdS/ZnS quantum dots. Transient absorption spectroscopic studies indicated that the charges can be effectively extracted and subsequently transferred to surrounding molecular substrates in a subpicosecond time scale in such hybrid nanocrystals. Based on density functional theory calculations, the ultrafast charge separation rates were ascribed to the formation of intermediate Au2S layer at the semiconductor-metal interface, which can successfully offset the energy confinement introduced by the ZnS shell. In conclusion, our findings not only provide insightful understandings on charge carrier dynamics in semiconductor-metal heterostructural materials but also pave the way for the future design of quantum dot-based hybrid photocatalytic systems.

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

Observations Show Charge Density of Volcanic Plumes is Higher Than Thunderstorms

We analyze slow electric field change and lightning mapping measurements to provide insight into the characteristics of volcanic lightning and the associated implications on charging processes and the charge structure of a Vulcanian eruption plume. Data were obtained during a multi-instrumental field campaign at Sakurajima volcano in 2015 when the Showa crater was active. We combine the electric field change and lightning mapping data from one explosive eruption on June 6, 2015 to identify individual flashes. From this, we interpret the flash type and polarity. In addition, the long-time constant of the electric field change instrument allowed measurement of the quasi-static field associated with charge separation in the eruption plume. We find that both intracloud and cloud-to-ground discharges occurred, and the polarity of cloud-to-ground discharges were all negative. The quasi-static field measurement showed the plume carried a net negative charge. We calculate both the total charge transferred by cloud-to-ground discharges and the net charge density of the eruption plume. We find that cloud-to-ground discharges transfer an average of –0.41C per flash and the net charge density was –33C/ km 3 . Here, the percent error is at least 200%, due to uncertainty in the antenna gain. We show that these estimates are consistent with lightning that is 100 m in length. Further, the average flash rate during the first 8 s following the onset of eruption was five flashes per second. After that time, the flash rate abruptly decreased, which may be related to the end of gas-thrust forcing.

58 GEOSCIENCES↗