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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 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Native Mass Spectrometry, Ion Mobility, Electron-Capture Dissociation, and Modeling Provide Structural Information for Gas-Phase Apolipoprotein E Oligomers

Apolipoprotein E (apoE) is an essential protein in lipid and cholesterol metabolism. Although the three common isoforms in humans differ only at two sites, their consequences in Alzheimer’s disease (AD) are dramatically different: only the ε4 allele is a major genetic risk factor for late-onset Alzheimer’s disease. The isoforms exist as a mixture of oligomers, primarily tetramer, at low μM concentrations in a lipid-free environment. This self-association is involved in equilibrium with the lipid-free state, and the oligomerization interface overlaps with the lipid-binding region. Elucidation of apoE wild-type (WT) structures at an oligomeric state, however, has not yet been achieved. To address this need, we used native electrospray ionization and mass spectrometry (native MS) coupled with ion mobility (IM) to examine the monomer and tetramer of the three WT isoforms. Although collision-induced unfolding (CIU) cannot distinguish the WT isoforms, the monomeric mutant (MM) of apoE3 shows higher stability when submitted to CIU than the WT monomer. From ion-mobility measurements, we obtained the collision cross section and built a coarse-grained model for the tetramer. Application of electron-capture dissociation (ECD) to the tetramer causes unfolding starting from the C-terminal domain, in good agreement with solution denaturation data, and provides additional support for the C4 symmetry structure of the tetramer. .

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Correlating structural and photochemical heterogeneity in cyanobacteriochrome NpR6012g4

Phytochrome photoreceptors control plant growth, development, and the shade avoidance response that limits crop yield in high-density agricultural plantings. Cyanobacteriochromes (CBCRs) are distantly related photosensory proteins that control cyanobacterial metabolism and behavior in response to light. Photoreceptors in both families reversibly photoconvert between two photostates via photoisomerization of linear tetrapyrrole (bilin) chromophores. Spectroscopic and biochemical reprorts have demonstrated heterogeneity in both photostates, but the structural basis for such heterogeneity remains unclear. We discuss solution NMR structures for both photostates of the red/green CBCR NpR6012g4 from Nostoc punctiforme . In addition to identifying structural changes accompanying photoconversion, these structures reveal structural heterogeneity for residues Trp655 and Asp657 in the red-absorbing NpR6012g4 dark state, yielding two distinct environments for the phycocyanobilin chromophore. We use site-directed mutagenesis and fluorescence and absorbance spectroscopy to assign an orange-absorbing population in the NpR6012g4 dark state to the minority configuration for Asp657. This population does not undergo full, productive photoconversion, as shown by time-resolved spectroscopy and absorption spectroscopy at cryogenic temperature. Our research thus elucidate the spectral and photochemical consequences of structural heterogeneity in a member of the phytochrome superfamily, insights that should inform efforts to improve photochemical or fluorescence quantum yields in the phytochrome superfamily.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Structural analysis of PseH, the Campylobacter jejuni N-acetyltransferase involved in bacterial O-linked glycosylation

Campylobacter jejuni is a bacterium that uses flagella for motility and causes worldwide acute gastroenteritis in humans. The C. jejuni N-acetyltransferase PseH (cjPseH) is responsible for the third step in flagellin O-linked glycosylation and plays a key role in flagellar formation and motility. cjPseH transfers an acetyl group from an acetyl donor, acetyl coenzyme A (AcCoA), to the amino group of UDP-4-amino-4,6-dideoxy-N-acetyl-β-L-altrosamine to produce UDP-2,4-diacetamido-2,4,6-trideoxy-β-L-altropyranose. To elucidate the catalytic mechanism of cjPseH, crystal structures of cjPseH alone and in complex with AcCoA were determined at 1.95 Å resolution. cjPseH folds into a single-domain structure of a central β-sheet decorated by four α-helices with two continuously connected grooves. A deep groove (groove-A) accommodates the AcCoA molecule. Interestingly, the acetyl end of AcCoA points toward an open space in a neighboring shallow groove (groove-S), which is occupied by extra electron density that potentially serves as a pseudosubstrate, suggesting that the groove-S may provide a substrate-binding site. Structure-based comparative analysis suggests that cjPseH utilizes a unique catalytic mechanism of acetylation that has not been observed in other glycosylation-associated acetyltransferases. Thus, our studies on cjPseH will provide valuable information for the design of new antibiotics to treat C. jejuni-induced gastroenteritis. - Highlights: • cjPseH adopts a single-domain structure of a central β-sheet decorated by α-helices. • cjPseH features two continuously connected grooves on the protein surface. • Acetyl coenzyme A (AcCoA) binds into a deep groove of cjPseH in an ‘L’ shape. • The acetyl end of AcCoA points to a wide groove, a potential substrate-binding site.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Structural insights into enzymatic [4+2] aza -cycloaddition in thiopeptide antibiotic biosynthesis

The [4+2] cycloaddition reaction is an enabling transformation in modern synthetic organic chemistry, but there are only limited examples of dedicated natural enzymes that can catalyze this transformation. Thiopeptides (or more formally thiazolyl peptides) are a class of thiazole-containing, highly modified, macrocyclic secondary metabolites made from ribosomally synthesized precursor peptides. The characteristic feature of these natural products is a six-membered nitrogenous heterocycle that is assembled via a formal [4+2] cycloaddition between two dehydroalanine (Dha) residues. This heteroannulation is entirely contingent on enzyme activity, although the mechanism of the requisite pyridine/dehydropiperidine synthase remains to be elucidated. The unusual aza -cylic product is distinct from the more common carbocyclic products of synthetic and biosynthetic [4+2] cycloaddition reactions. Here, to elucidate the mechanism of cycloaddition, we have determined atomic resolution structures of the pyridine synthases involved in the biosynthesis of the thiopeptides thiomuracin (TbtD) and GE2270A (PbtD), in complex with substrates and product analogs. Structure-guided biochemical, mutational, computational, and binding studies elucidate active-site features that explain how orthologs can generate rigid macrocyclic scaffolds of different sizes. Notably, the pyridine synthases show structural similarity to the elimination domain of lanthipeptide dehydratases, wherein insertions of secondary structural elements result in the formation of a distinct active site that catalyzes different chemistry. Comparative analysis identifies other catalysts that contain a shared core protein fold but whose active sites are located in entirely different regions, illustrating a principle predicted from efforts in de novo protein design.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

In Situ TEM for Structural and Chemical Evolutions of Bimetallic Pt–Ni Nanoparticles at Elevated Temperatures: Implications for Heterogeneous Catalysis

Platinum-based bimetallic nanoparticles (NPs) are of great interest for their applications in catalysis. The catalytic properties of these NPs are significantly dependent on their morphology, structure, and composition, whose response to thermal input remains challenging to be fully understood. This study investigates the thermally induced structural and chemical evolutions of single-crystalline Pt-Ni NPs using in situ transmission electron microscopy. The observed morphological evolution includes the facet development from a truncated octahedron to a spherical-like isotropic shape, followed by the formation of pancake-like ellipsoid shape at high temperatures due to surface atom migration and interfacial wetting enabled by the particle-substrate interaction. Comparative investigations by in situ scanning transmission electron microscopy with energy dispersive X-ray spectroscopy mapping elucidate that the solid-solution compositional configuration can be retained over a large temperature range, while core-shell NPs undergo irreversible solid-solution transitions through chemical homogenization at elevated temperatures. Finally, these findings elucidate the effect of thermal input on structural evolution and compositional redistribution of Pt-Ni bimetallic NPs, offering valuable insights into the design of heterogeneous catalysts.

25 ENERGY STORAGE↗
DOE OSTI2017

Structure and function of the divalent anion/Na + symporter from Vibrio cholerae and a humanized variant

Integral membrane proteins of the divalent anion/Na + symporter (DASS) family translocate dicarboxylate, tricarboxylate or sulphate across cell membranes, typically by utilizing the preexisting Na + gradient. The molecular determinants for substrate recognition by DASS remain obscure, largely owing to the absence of any substrate-bound DASS structure. Here we present 2.8-Å resolution X-ray structures of VcINDY, a DASS from Vibrio cholerae that catalyses the co-transport of Na + and succinate. These structures portray the Na + -bound VcINDY in complexes with succinate and citrate, elucidating the binding sites for substrate and two Na + ions. Furthermore, we report the structures of a humanized variant of VcINDY in complexes with succinate and citrate, which predict how a human citrate-transporting DASS may interact with its bound substrate. Our findings provide insights into metabolite transport by DASS, establishing a molecular basis for future studies on the regulation of this transport process.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

(Pt{sub 1–x}Cu{sub x}){sub 3}Cu{sub 2}B and Pt{sub 9}Cu{sub 3}B{sub 5}, the first examples of copper platinum borides. Observation of superconductivity in a novel boron filled β-Mn-type compound

New ternary copper platinum borides have been synthesized by arc melting of pure elements followed by annealing at 600 °C. The structures have been studied by X-ray single crystal and powder diffraction. (Pt{sub 1−x}Cu{sub x}){sub 3}Cu{sub 2}B (x=0.33) forms a B-filled β-Mn-type structure (space group P4{sub 1}32; a=0.6671(1) nm). Cu atoms are distributed preferentially on the 8c atom sites, whereas the 12d site is randomly occupied by Pt and Cu atoms (0.670(4) Pt±0.330(4) Cu). Boron is located in octahedral voids of the parent β-Mn-type structure. Pt{sub 9}Cu{sub 3}B{sub 5} (space group P-62m; a=0.9048(3) nm, c=0.2908(1) nm) adopts the Pt{sub 9}Zn{sub 3}B{sub 5–δ}-type structure. It has a columnar architecture along the short translation vector exhibiting three kinds of [Pt{sub 6}] trigonal prism columns (boron filled, boron semi-filled and empty) and Pt channels with a pentagonal cross section filled with Cu atoms. The striking structural feature is a [Pt{sub 6}] cluster in form of an empty trigonal prism at the origin of the unit cell, which is surrounded by coupled [BPt{sub 6}] and [Pt{sub 6}] trigonal prisms, rotated perpendicularly to the central one. There is no B–B contact as well as Cu–B contact in the structure. The relationships of Pt{sub 9}Cu{sub 3}B{sub 5} structure with the structure of Ti{sub 1+x}Os{sub 2−x}RuB{sub 2} as well as with the structure families of metal sulfides and aluminides have been elucidated. (Pt{sub 1–x}Cu{sub x}){sub 3}Cu{sub 2}B (x=0.3) (B-filled β-Mn-type structure) is a bulk superconductor with a transition temperature of about 2.06 K and an upper critical field μ{sub 0}H{sub C2}(0){sup WHH} of 1.2 T, whereas no superconducting transition has been observed up to 0.3 K in Pt{sub 9}Cu{sub 3}B{sub 5} (Pt{sub 9}Zn{sub 3}B{sub 5–δ}-type structure) from electrical resistivity measurements. - Highlights: • First two copper platinum borides, (Pt{sub 0.67}Cu{sub 0.33}){sub 3}Cu{sub 2}B and Pt{sub 9}Cu{sub 3}B{sub 5} were obtained. • (Pt{sub 0.67}Cu{sub 0.33}){sub 3}Cu{sub 2}B forms a B-filled β-Mn-type structure. • Pt{sub 9}Cu{sub 3}B{sub 5} adopts a Pt{sub 9}Zn{sub 3}B{sub 5–δ}-type structure. • Boron atoms exhibit octahedral and trigonal prismatic coordination. • (Pt{sub 1–x}Cu{sub x})3Cu{sub 2}B (x=0.3) is a bulk superconductor with T{sub c} 2.06 K.

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

Structural basis underlying the synergism of NADase and SLO during group A Streptococcus infection

Group A Streptococcus (GAS) is a strict human pathogen possessing a unique pathogenic trait that utilizes the cooperative activity of NAD + -glycohydrolase (NADase) and Streptolysin O (SLO) to enhance its virulence. How NADase interacts with SLO to synergistically promote GAS cytotoxicity and intracellular survival is a long-standing question. Here, the structure and dynamic nature of the NADase/SLO complex are elucidated by X-ray crystallography and small-angle scattering, illustrating atomic details of the complex interface and functionally relevant conformations. Structure-guided studies reveal a salt-bridge interaction between NADase and SLO is important to cytotoxicity and resistance to phagocytic killing during GAS infection. Furthermore, the biological significance of the NADase/SLO complex in GAS virulence is demonstrated in a murine infection model. Overall, this work delivers the structure-functional relationship of the NADase/SLO complex and pinpoints the key interacting residues that are central to the coordinated actions of NADase and SLO in the pathogenesis of GAS infection.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

The Influence of Structure and Processing on the Behavior of TiO 2 Protective Layers for Stabilization of n-Si/TiO 2 /Ni Photoanodes for Water Oxidation

Light absorbers with moderate band gaps (1–2 eV) are required for high-efficiency solar fuels devices, but most semiconducting photoanodes undergo photocorrosion or passivation in aqueous solution. Amorphous TiO 2 deposited by atomic-layer deposition (ALD) onto various n-type emiconductors (Si,GaAs, GaP, and CdTe) and coated with thin films or islands of Ni produces efficient, stable photoanodes for water oxidation, with the TiO 2 films protecting the underlying semiconductor from photocorrosion in pH = 14 KOH(aq). The links between the electronic properties of the TiO 2 in these electrodes and the structure and energetic defect states of the material are not yet well-elucidated. We show herein that TiO 2 films with a variety of crystal structures and mid-gap defect state distributions, deposited using both ALD and sputtering, form rectifying junctions with n-Si and are highly conductive towards photogenerated carriers in n-Si/TiO 2 /Ni photoanodes. Moreover, the photovoltage of these electrodes can be modified by annealing the TiO 2 in reducing or oxidizing environments. All of the polycrystalline TiO 2 films with compact grain boundaries investigated herein protected the n-Si photoanodes against photocorrosion in pH = 14 KOH(aq). Hence, in these devices conduction through the TiO 2 layer is neither specific to a particular amorphous or crystalline structure nor determined wholly by a particular extrinsic dopant impurity. The coupled structural and energetic properties of TiO 2 , and potentially other protective oxides, can therefore be controlled to yield optimized photoelectrode performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Perspective: How good is DFT for water?

Kohn-Sham density functional theory (DFT) has become established as an indispensable tool for investigating aqueous systems of all kinds, including those important in chemistry, surface science, biology, and the earth sciences. Nevertheless, many widely used approximations for the exchange-correlation (XC) functional describe the properties of pure water systems with an accuracy that is not fully satisfactory. The explicit inclusion of dispersion interactions generally improves the description, but there remain large disagreements between the predictions of different dispersion-inclusive methods. We present here a review of DFT work on water clusters, ice structures, and liquid water, with the aim of elucidating how the strengths and weaknesses of different XC approximations manifest themselves across this variety of water systems. Our review highlights the crucial role of dispersion in describing the delicate balance between compact and extended structures of many different water systems, including the liquid. By referring to a wide range of published work, we argue that the correct description of exchange-overlap interactions is also extremely important, so that the choice of semi-local or hybrid functional employed in dispersion-inclusive methods is crucial. The origins and consequences of beyond-2-body errors of approximate XC functionals are noted, and we also discuss the substantial differences between different representations of dispersion. We propose a simple numerical scoring system that rates the performance of different XC functionals in describing water systems, and we suggest possible future developments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

DE-NE0000724 - Research Performance Final Report - Investigation of Thermal Aging Effects on the Evolution of Microstructure and Mechanical Properties of Cast Duplex Stainless Steels

This report details the research activities carried out under DOE-NEUP award number DE-NE0000724 concerning the evolution of structural and mechanical properties during thermal aging of CF–3 and CF–8 cast duplex stainless steels (CDSS). The overall objective of this project was to use state-of-the-art characterization techniques to elucidate trends and phenomena in the mechanical and structural evolution of cast duplex stainless steels (CDSS) during thermal aging. These steels are commonly used as structural materials in commercial light water nuclear power plants, undergoing aging for decades in operation as cooling water pipes, pump casings, valve bodies, etc. During extended exposure to these conditions, CDSS are known to undergo a change in mechanical properties resulting in a loss of ductility, i.e. embrittlement. While it is generally accepted that structural changes within the ferrite phase, such as decomposition into iron (Fe)-rich and chromium (Cr)-rich domains, lead to the bulk embrittlement of the steels, many questions remain as to the mechanisms of embrittlement at multiple length scales. This work is intended to shed insight into the atomic level composition changes, associated kinetic mechanisms, and effects of changing phase structure on micro- and nano-scale deformation that lead to loss of impact toughness and tensile ductility in these steels. In general, this project provides a route to answer some of these major questions using techniques such as 3-dimensional (3-D) atom probe tomography (APT) and real-microstructure finite element method (FEM) modeling, which were not readily available when these steels were originally selected for service in light water reactors. Mechanical properties evaluated by Charpy V-notch impact testing (CVN), tensile testing, and microhardness and nanohardness measurements were obtained for each condition and compared with the initial baseline properties to view trends in deformation behavior during aging. Concurrent analysis of the microstructure and nanostructure by atom probe tomography (APT) and transmission electron microscopy (TEM) provide mechanistic insight into the kinetic and mechanical behavior occurring on the nano-scale. The presence and morphology of the ferrite, austenite, and carbide phases have been characterized, and formation of new phases during aging, including spinodal decomposition products (α- and α'-ferrite) and G-phase, have been observed. The mechanical and structural characterization have been used to create accurate FEM models based on the real micro- and nano-structures of the systems. These models provide new insight into the local deformation behavior of these steels and the effects of each individual phase (including ferrite, austenite, carbides, and spinodal decomposition products) on the evolving bulk mechanical behavior of the system. The project was divided into three major tasks: 1. Initial Microstructure and Mechanical Property Survey and Initiate Heat Treatment; 2. Microstructural Characterization and Mechanical Property Testing During Aging; and 3. Microstructure-based Finite Element Modeling. Each of these tasks was successfully executed, resulting in reliable data and analysis that add to the overall body of work on the CDSS materials. Baseline properties and aging trends in mechanical data confirm prior observations and add new insights into the mechanical behavior of the steels. Structural characterization on multiple length scales provides new information on phase changes occurring during aging and sheds light on the kinetic processes occurring at the atomic scale. Furthermore, a combination of mechanical testing and microstructural characterization techniques was utilized to design FEM models of local deformation behavior of the ferrite and austenite phases, providing valuable new information regarding the effects of each of the microstructural components on the hardening and embrittlement processes. The data and analysis presented in this report and the publication associated with this project (§V) increase the understanding of aging and deformation in CF–3 and CF–8 steels. These results provide valuable information that can be utilized to aid in making informed decisions regarding the ongoing use of these steels in commercial nuclear infrastructure.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2022

Polyacrylonitrile-based electrolytes: How processing and residual solvent affect ion transport and stability

Polyacrylonitrile (PAN) is one of the alternative candidate polymer hosts to form solid polymer electrolytes (SPEs) besides the widely used poly(ethylene oxide). In this study, we systematically investigate the processing of PAN based SPEs containing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, using dimethylformamide (DMF) as the solvent. The effects of PAN processing procedure including solution mixing, casting, and drying on the morphology, ion transport, solvation structure, Li and oxidative stability of PAN electrolytes are thoroughly examined. In particular, four drying conditions are investigated and the amount of residual DMF is accurately determined using infrared (IR) spectroscopy. Varying the drying conditions can lead to five orders of magnitude decrease in the ionic conductivity. As DMF content decreases, the SPE's stability again Li metal dramatically improves. The practical oxidative stability is also strongly affected by the residual DMF content, ranging from 2.5 V to 3.5 V, much lower than reported values. Finally, the role of the residual DMF solvent is elucidated. DMF content vitally influences ion solvation structure at different concentration regimes, which ultimately dictates the ion conduction mechanism and oxidative stability of PAN based SPEs. In conclusion, this thorough study lays the groundwork for future development of PAN based electrolytes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Structure of the Intermediate Filament-Binding Region of Desmoplakin

Here, desmoplakin (DP) is a cytoskeletal linker protein that connects the desmosomal cadherin/plakoglobin/plakophilin complex to intermediate filaments (IFs). The C-terminal region of DP (DPCT) mediates IF binding, and contains three plakin repeat domains (PRDs), termed PRD-A, PRD-B and PRD-C. Previous crystal structures of PRDs B and C revealed that each is formed by 4.5 copies of a plakin repeat (PR) and has a conserved positively charged groove on its surface. Although PRDs A and B are linked by just four amino acids, B and C are separated by a 154 residue flexible linker, which has hindered crystallographic analysis of the full DPCT. Here we present the crystal structure of a DPCT fragment spanning PRDs A and B, and elucidate the overall architecture of DPCT by small angle X-ray scattering (SAXS) analysis. The structure of PRD-A is similar to that of PRD-B, and the two domains are arranged in a quasi-linear arrangement, and separated by a 4 amino acid linker. Analysis of the B-C linker region using secondary structure prediction and the crystal structure of a homologous linker from the cytolinker periplakin suggests that the N-terminal ~100 amino acids of the linker form two PR-like motifs. SAXS analysis of DPCT indicates an elongated but non-linear shape with R g = 51.5 Å and D max = 178 Å. These data provide the first structural insights into an IF binding protein containing multiple PRDs and provide a foundation for studying the molecular basis of DP-IF interactions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Atomic-scale Imaging of Magnetic and Electronic Orders in Complex Oxides (Final Technical Report)

This research project aimed to expand spin‐polarized scanning tunneling microscopy (SP‐STM) imaging to complex quantum materials, initially focusing on uncovering the magnetic structure of doped Iridium‐based oxides (iridates) with subatomic precision. Chemical doping of complex oxides has led to exciting discoveries over the past few decades, such as high-temperature superconductivity and colossal magnetoresistance. However, the process of chemical doping is often accompanied by spatial inhomogeneity, characterized by nanometer-scale variations in electronic and/or magnetic properties of the material. SP-STM can in principle be used to image magnetic properties, but SP-STM has historically been applied primarily to relatively simple magnetic materials and nanostructures. The main objectives of this project included: (1) visualizing the evolution of magnetism in iridates, as a function of charge carrier doping, temperature and energy, (2) elucidating the relationship between the inhomogeneous electronic structure and magnetism at the nanoscale, and (3) searching for signatures of new magnetic phases in iridates and other quantum materials. Advanced STM and SP-STM imaging was also applied to select kagome metals and superconductors. The comprehensive experimental approach developed in this project provided a foundation to study quantum materials in which spin, charge and orbital degrees of freedom intertwine to create new states of matter.

36 MATERIALS SCIENCE↗
DOE OSTI2022

The role of coverage effects on the structure–sensitivity of formic acid electrooxidation on Pd surfaces

Direct formic acid (FA) fuel cells (DFAFCs) with Pd anode catalysts are promising for small portable applications. During the electrooxidation of formic acid (FAO), CO accumulates on the Pd electrocatalyst, thereby decreasing its performance. In this work, we use density functional theory (DFT; RPBE) to elucidate the significance of coverage effects on the structure–sensitivity of FAO over four low–index Pd surfaces: Pd(1 1 1), Pd(1 0 0), Pd(1 1 0), and Pd(2 1 1). We construct coverage–dependent Gibbs free energy diagrams and in agreement with experiment, predict that Pd(1 0 0) and Pd(2 1 1) are the most active surfaces. Additionally, we find that the presence of CO spectator species can alter the preferred electrooxidation pathway under different applied potentials. Furthermore, such pathway transitions appear to be critical for rationalizing experimental trends regarding electrocatalytic activity and are only captured when coverage effects are accounted for. Insights derived from this work may facilitate the design of improved FAO electrocatalysts.

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

Correlation of Broad Absorption Band with Small Singlet‐Triplet Energy Gap in Organic Photovoltaics

Abstract Organic photovoltaics (OPV) are one of the most effective ways to harvest renewable solar energy, with the power conversion efficiency (PCE) of the devices soaring above 19 % when processed with halogenated solvents. The superior photocurrent of OPV over other emerging photovoltaics offers more opportunities to further improve the efficiency. Tailoring the absorption band of photoactive materials is an effective way to further enhance OPV photocurrent. However, the field has mostly been focusing on improving the near‐infrared region photo‐response, with the absorption shoulders in short‐wavelength region (SWR) usually being neglected. Herein, by developing a series of non‐fullerene acceptors (NFAs) with varied side‐group conjugations, we observe an enhanced SWR absorption band with increased side‐group conjugation length. The underpinning factors of how molecular structures and geometries improve SWR absorption are clearly elucidated through theoretical modelling and crystallography. Moreover, a clear relationship between the enhanced SWR absorption and reduced singlet‐triplet energy gap is established, both of which are favorable for the OPV performance and can be tailored by rational structure design of NFAs. Finally, the rationally designed NFA, BO‐TTBr, affords a decent PCE of 18.5 % when processed with a non‐halogenated green solvent.

Chemistry↗