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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 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Carrier control in Sn–Pb perovskites via 2D cation engineering for all-perovskite tandem solar cells with improved efficiency and stability

All-perovskite tandem solar cells are promising for achieving photovoltaics with power conversion efficiencies above the detailed balance limit of single-junction cells, while retaining the low cost, light weight and other advantages associated with metal halide perovskite photovoltaics. However, the efficiency and stability of all-perovskite tandem cells are limited by the Sn-Pb-based narrow-bandgap perovskite cells. Here we show that the formation of quasi-two-dimensional (quasi-2D) structure (PEA) 2 GAPb 2 I 7 from additives based on mixed bulky organic cations phenethylammonium (PEA+) and guanidinium (GA+) provides critical defect control to substantially improve the structural and optoelectronic properties of the narrow-bandgap (1.25 eV) Sn-Pb perovskite thin films. Additionally, this 2D additive engineering results in Sn-Pb-based absorbers with low dark carrier density (~1.3 x 10 14 cm -3 ), long bulk carrier lifetime (~9.2 us) and low surface recombination velocity (~1.4 cm s -1 ), leading to 22.1%-efficient single-junction Sn-Pb perovskite cells and 25.5%-efficient all-perovskite two-terminal tandems with high photovoltage and long operational stability.

14 SOLAR ENERGY↗
DOE OSTI2018

Microbial formation of stable soil carbon is more efficient from belowground than aboveground input

The relative contributions of aboveground versus belowground plant carbon inputs to the stable soil organic carbon pool are the subject of much debate—with direct implications for how the carbon cycle is modelled and managed. Additionally, the belowground rhizosphere pathway (that is, carbon exiting the living root) is theorized to form stable soil carbon more efficiently than the aboveground pathway. However, while several mechanisms have been invoked to explain this efficiency, few have been empirically tested or quantified. Here, we use soil microcosms with standardized carbon inputs to investigate three posited mechanisms that differentiate aboveground from belowground input pathways of dissolved organic carbon—through the microbial biomass—to the mineral-stabilized soil organic carbon pool: (1) the physical distance travelled, (2) the microbial abundance in the region in which a carbon compound enters (that is, rhizosphere versus bulk soil) and (3) the frequency and volume of carbon delivery (that is, infrequent ‘pulse’ versus frequent ‘drip’). We demonstrate that through the microbial formation pathway, belowground inputs form mineral-stabilized soil carbon more efficiently than aboveground inputs, partly due to the greater efficiency of formation by the rhizosphere microbial community relative to the bulk soil community. However, we show that because the bulk soil has greater capacity to form mineral-stabilized soil carbon due to its greater overall volume, the relative contributions of aboveground versus belowground carbon inputs depend strongly on the ratio of rhizosphere to bulk soil.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

On-demand formation of Lewis bases for efficient and stable perovskite solar cells

In the fabrication of FAPbI 3 -based perovskite solar cells, Lewis bases play a crucial role in facilitating the formation of the desired photovoltaic α-phase. However, an inherent contradiction exists in their role: they must strongly bind to stabilize the intermediate δ-phase, yet weakly bind for rapid removal to enable phase transition and grain growth. To resolve this conflict, we introduced an on-demand Lewis base molecule formation strategy. This approach utilized Lewis-acid-containing organic salts as synthesis additives, which deprotonated to generate Lewis bases precisely when needed and could be reprotonated back to salts for rapid removal once their role is fulfilled. This method promoted the optimal crystallization of α-phase FAPbI 3 perovskite films, ensuring the uniform vertical distribution of A-site cations, larger grain sizes and fewer voids at buried interfaces. Perovskite solar cells incorporating semicarbazide hydrochloride achieved an efficiency of 26.1%, with a National Renewable Energy Laboratory-certified quasi-steady-state efficiency of 25.33%. These cells retained 96% of their initial efficiency after 1,000 h of operation at 85 °C under maximum power point tracking. Additionally, mini-modules with an aperture area of 11.52 cm 2 reached an efficiency of 21.47%. This strategy is broadly applicable to all Lewis-acid-containing organic salts with low acid dissociation constants and offers a universal approach to enhance the performance of perovskite solar cells and modules.

14 SOLAR ENERGY↗
DOE OSTI2022

Defect engineering in wide-bandgap perovskites for efficient perovskite–silicon tandem solar cells

Wide-bandgap (WBG) mixed-halide perovskites show promise of realizing efficient tandem solar cells but at present suffer from large open-circuit voltage loss and the mechanism is still unclear. Here we show that WBG perovskites with iodide–bromide compositions have an increased concentration of deep traps induced by iodide interstitials, which limits performance of WBG perovskite cells. We employ tribromide ions to suppress the iodide interstitial formation and thus reduce charge recombination in bladed WBG perovskite films of Cs 0.1 FA 0.2 MA 0.7 Pb(I 0.85 Br 0.15 )3. The 1-µm-thick opaque WBG perovskite solar cells have an efficiency of 21.9%, a small open-circuit voltage deficit of 0.40 V and a large fill factor of 83%. The efficiency of the best-performing monolithic perovskite–silicon tandem cell using this perovskite reaches 28.6%. Furthermore, the tribromide addition also suppresses light-induced phase segregation in WBG perovskites and thus enhance device stability. Encapsulated tandem cells maintain 93% of their initial efficiency after operation for 550 h.

14 SOLAR ENERGY↗
DOE OSTI2018

Efficient and stable emission of warm-white light from lead-free halide double perovskites

Lighting accounts for one-fifth of global electricity consumption. Single materials with efficient and stable white-light emission are ideal for lighting applications, but photon emission covering the entire visible spectrum is difficult to achieve using a single material. Metal halide perovskites have outstanding emission properties; however, the best-performing materials of this type contain lead and have unsatisfactory stability. Here we report a lead-free double perovskite that exhibits efficient and stable white-light emission via self-trapped excitons that originate from the Jahn–Teller distortion of the AgCl 6 octahedron in the excited state. By alloying sodium cations into Cs 2 AgInCl 6 , we break the dark transition (the inversion-symmetry-induced parity-forbidden transition) by manipulating the parity of the wavefunction of the self-trapped exciton and reduce the electronic dimensionality of the semiconductor. This leads to an increase in photoluminescence efficiency by three orders of magnitude compared to pure Cs 2 AgInCl 6 . The optimally alloyed Cs 2 (Ag 0.60 Na 0.40 )InCl 6 with 0.04 per cent bismuth doping emits warm-white light with 86 ± 5 per cent quantum efficiency and works for over 1,000 hours. We anticipate that these results will stimulate research on single-emitter-based white-light-emitting phosphors and diodes for next-generation lighting and display technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Efficiency-optimized relativistic plasma harmonics for extreme fields

Bright harmonic radiation from relativistically oscillating laser plasmas offers a direct route for generating extreme electromagnetic fields. Theory predicts that under optimized conditions, the plasma medium can support strong spatiotemporal compression of laser energy in a coherent harmonic focus (CHF), delivering intensity boosts many orders of magnitude greater than the incident driving laser pulse. Although diffraction-limited performance (spatial compression) and attosecond phase locking (temporal compression) have been demonstrated experimentally, efficient coupling of relativistically intense laser pulse energy into the emitted harmonic cone has not been realized so far. Here we demonstrate that this highly nonlinear interaction can be tailored to deliver the maximum conversion efficiencies predicted from simulations. By fine-tuning the temporal profile of the driving laser on sub-picosecond (<10 −12 s) timescales, energies >9 mJ between the 12th and 47th harmonics are observed. These results are in agreement with the theoretically expected efficiency dependence on harmonic order, verifying that optimal conditions have been achieved in the generation process. This is the important final element required to achieve the expected intensity boosts from a CHF in experiments. Although obtaining spatiotemporal compression and optimal efficiency simultaneously remains challenging, the path to realizing extreme optical field strengths approaching the critical field of quantum electrodynamics (the Schwinger limit at >10 16 V cm −1 or >10 29 W cm −2 ) is now open, permitting all-optical studies of the quantum vacuum and new frontiers for intense attosecond science.

High-harmonic generation↗
DOE OSTI2024

Mitochondrial ATP generation is more proteome efficient than glycolysis

Metabolic efficiency profoundly influences organismal fitness. Nonphotosynthetic organisms, from yeast to mammals, derive usable energy primarily through glycolysis and respiration. Although respiration is more energy efficient, some cells favor glycolysis even when oxygen is available (aerobic glycolysis, Warburg effect). A leading explanation is that glycolysis is more efficient in terms of ATP production per unit mass of protein (that is, faster). Through quantitative flux analysis and proteomics, we find, however, that mitochondrial respiration is actually more proteome efficient than aerobic glycolysis. This is shown across yeast strains, T cells, cancer cells, and tissues and tumors in vivo. Instead of aerobic glycolysis being valuable for fast ATP production, it correlates with high glycolytic protein expression, which promotes hypoxic growth. Aerobic glycolytic yeasts do not excel at aerobic growth but outgrow respiratory cells during oxygen limitation. Here, we accordingly propose that aerobic glycolysis emerges from cells maintaining a proteome conducive to both aerobic and hypoxic growth.

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

High efficiency laser resonance ionization of plutonium

Three-step resonance photoionization spectra of plutonium have been studied with Ti:Sapphire lasers for the development of efficient laser ionization schemes for ultra-trace analysis of Pu isotopes by resonance ionization mass spectrometry. We observed eighteen intermediate excited states of even parity in the energy range 35568–36701 cm -1 , thirteen of them have not been previously documented, and a larger number of high-lying excited states and autoionizing states of odd-parity between 48238 and 49510 cm -1 . Three-color, three-photon ionization schemes via six intermediate states were evaluated under similar ion source operating conditions. This led to a highly efficient three-step scheme with an overall ionization efficiency of 51.1±1.3%, which is an order of magnitude improvement over the previously reported ionization efficiency for Pu.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Depolymerizable and recyclable luminescent polymers with high light-emitting efficiencies

Luminescent polymers are of great interest in a number of photonic technologies, including electroluminescence, bioimaging, medical diagnosis, bio-stimulation and security signage. Incorporating depolymerizability and recyclability into luminescent polymers is pivotal for promoting their sustainability and minimizing their environmental impacts at the end of the product lifecycle, but existing strategies often compromise the light-emitting efficiencies. Here, in this study, we develop a strategy that utilizes cleavable moiety to create depolymerizable and recyclable thermally activated delayed fluorescence (TADF) polymers without compromising their high light-emitting efficiencies. The electroluminescent devices based on the TADF polymers achieved a high external quantum efficiency of up to 15.1 %. The TADF polymers can be depolymerized under either mild acidic or heating conditions, with precise control of the kinetics, and the obtained pure monomers can potentially be isolated and repolymerized for subsequent life applications. This work promotes the end-of-life environmental friendliness and circularity of luminescent materials, paving the way to a sustainable photonic industry. Developing depolymerizable and recyclable polymers with high light-emitting efficiencies is of vital importance for sustainable photonic technologies, but remains challenging. Here the authors design a strategy to develop such polymers based on the use of controllable cleavable moiety.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Constraining CO coverage on copper promotes high-efficiency ethylene electroproduction

The availability of inexpensive industrial CO gas streams motivates efficient electrocatalytic upgrading of CO to higher-value feedstocks such as ethylene. However, the electrosynthesis of ethylene by the CO reduction reaction (CORR) has suffered from low selectivity and energy efficiency. Here we find that the recent strategy of increasing performance through use of highly alkaline electrolyte—which is very effective in CO 2 RR—fails in CORR and drives the reaction to acetate. We then observe that ethylene selectivity increases when we constrain (decrease) CO availability. Using density functional theory, we show how CO coverage on copper influences the reaction pathways of ethylene versus oxygenate: lower CO coverage stabilizes the ethylene-relevant intermediates whereas higher CO coverage favours oxygenate formation. We then control local CO availability experimentally by tuning the CO concentration and reaction rate; we achieve ethylene Faradaic efficiencies of 72% and a partial current density of >800 mA cm -2 . The overall system provides a half-cell energy efficiency of 44% for ethylene production.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Energy-efficient scientific computing using chemical reservoirs

The rapid growth of computing demands driven by scientific computing, data analytics, and artificial intelligence (AI) advancements has exposed the limitations of traditional digital processing systems. These systems are nearing physical energy barriers, making significant gains in energy efficiency increasingly unattainable. As we advance toward post-exascale computing, disruptive approaches are critical to overcoming these limitations. Among emerging analog solutions, biochemical computing offers a transformative path for achieving orders-of-magnitude improvements in energy efficiency. By leveraging the natural optimization capabilities of chemical reaction networks (CRNs), biochemical systems have the potential to meet high-performance computing needs through natural scalability. However, numerous challenges remain, including theoretical limitations in mapping computational problems to CRNs and practical barriers in implementing biochemical computing devices. In this paper, we present a framework for chemical computation using biochemical systems and introduce key components of our approach for energy-efficient scientific computing. We showcase the feasibility of this framework by solving a system of ordinary differential equations by emulating a chemical reservoir device, demonstrating its potential for addressing modern computing challenges. This work lays a foundational step toward harnessing the computational power of chemistry to design energy-efficient, scalable, high-performance next-generation computing systems.

Johnson, Connah G. M. [Pacific Northwest National ↗
DOE OSTI2016

Optimisation of GaN LEDs and the reduction of efficiency droop using active machine learning

A fundamental challenge in the design of LEDs is to maximise electro-luminescence efficiency at high current densities. We simulate GaN-based LED structures that delay the onset of efficiency droop by spreading carrier concentrations evenly across the active region. Statistical analysis and machine learning effectively guide the selection of the next LED structure to be examined based upon its expected efficiency as well as model uncertainty. This active learning strategy rapidly constructs a model that predicts Poisson-Schrödinger simulations of devices, and that simultaneously produces structures with higher simulated efficiencies.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2017

Novel high-efficiency visible-light responsive Ag 4 (GeO 4 ) photocatalyst

A novel high-efficiency visible-light responsive Ag 4 (GeO 4 ) photocatalyst was prepared by a facile hydrothermal method. The photocatalytic activity of as-prepared Ag 4 (GeO 4 ) was evaluated by photodegradation of methylene blue (MB) dye and water splitting experiments. The photodegradation efficiency and oxygen production efficiency of Ag 4 (GeO 4 ) were detected to be 2.9 and 1.9 times higher than those of Ag 2 O. UVvis diffuse reflectance spectroscopy (DRS), photoluminescence experiment and photoelectric effect experiments prove that the good light response and high carrier separation efficiency facilitated by the internal electric field are the main reasons for Ag 4 (GeO 4 )'s excellent catalytic activity. Radical-trapping experiments reveal that the photogenerated holes are the main active species. Lastly, first-principles theoretical calculations provide more insight into understanding the photocatalytic mechanism of the Ag 4 (GeO 4 ) catalyst.

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

Unassisted solar water splitting with 9.8% efficiency and over 100 h stability based on Si solar cells and photoelectrodes catalyzed by bifunctional Ni–Mo/Ni

Designing a highly efficient and stable photoelectrochemical (PEC) tandem cell for unassisted solar water splitting is considered a promising approach for large-scale solar energy storage. To date, various tandem device configurations have been reported. However, the achievement of a solar-to-hydrogen conversion efficiency (η STH ) of 10% is still full of challenges, due to the incompatibility between the two photoelectrode materials. Here, we report a highly efficient and stable photovoltaic (PV)–PEC tandem device composed of a dual Si photoelectrode and two series-connected ordinary Si PV cells. The dual-photoelectrode device consists of an n + np + -Si photocathode and p + pn + -Si photoanode, which allow back illumination from the Si substrate, spatially and functionally decoupling the optical absorption and the catalytic activity. By further employing a Ni protective layer together with a bifunctional Ni–Mo catalyst for both the Si photocathode and photoanode, the PV–PEC tandem cell can perform spontaneous water splitting without any applied bias. A high η STH of 9.8% with a stability of over 100 h was achieved in alkaline solution under parallel AM 1.5G 1 sun illumination. Furthermore, this work essentially allows a modular independent optimization of each component which can enhance the efficiency and stability of the PV–PEC cells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

The importance of phase equilibrium for doping efficiency: iodine doped PbTe

Semiconductor engineering relies heavily on doping efficiency and dopability. Low doping efficiency may cause low mobility and failure to reach target carrier concentrations or even the desired carrier type. Semiconducting thermoelectric materials perform best with degenerate carrier concentrations, meaning high performance in new materials might not be realized experimentally without a route to optimal doping. Doping in the classic PbTe thermoelectric system has been largely successful but reported doping efficiencies can vary, raising concerns about reproducibility. Here, we stress the importance of phase equilibria considerations during synthesis to avoid undesired intrinsic defects leading to sub-optimal doping. By saturation annealing at 973 K, we decidedly fix the composition in single crystal iodine-doped PbTe samples to be Pb-rich or Te-rich without introducing impurity phases. We show that, regardless of iodine concentration, degenerate n-type carrier concentrations with ideal doping efficiency require Pb-rich compositions. Electrons in Te-rich samples are heavily compensated by charged intrinsic Pb vacancy defects. From Hall effect measurements and a simple defect model supported by modern defect calculations, we map out the 973 K ternary Pb–Te–I phase diagram to explicitly link carrier concentration and composition. Furthermore, we discuss unintentional composition changes due to loss of volatile Te during synthesis and measurements. The methods and concepts applied here may guide doping studies on other lead chalcogenide systems as well as any doped, complex semiconductor.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Exploiting heat transfer to achieve efficient photoelectrochemical CO 2 reduction under light concentration

Photoelectrochemical (PEC) conversion of carbon dioxide into valuable chemicals and fuels represents a promising path towards combating anthropogenic CO 2 emissions. However, the limited conversion efficiencies, operation lifetimes and CO 2 utilization efficiencies of PEC devices currently prohibit their application beyond the laboratory scale. Here, a wireless device converting CO 2 and water into carbon monoxide and hydrogen at a peak solar conversion efficiency exceeding 16% under an illumination intensity of 5 suns is demonstrated. A CO/H 2 product ratio between 10–20 is measured during a 17 h stability test. Fluctuations in device performance are rigorously analyzed via deconvolution of electrochemical and photoabsorber contributions. Furthermore, it is demonstrated that beneficial heat dissipation is enabled by wireless integration of the photoabsorber and electrocatalyst components, accounting for roughly 10% of the achieved conversion efficiency, an achievement unattainable with physically separated photoabsorber and electrolyzer components.

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

Reducing sputter induced stress and damage for efficient perovskite/silicon tandem solar cells

Reducing damages caused by sputtering of transparent conductive oxide (TCO) electrodes is critical in achieving highly efficient and stable perovskite/silicon tandem solar cells. Here we study the sputter caused damage to bathocuproine (BCP), which is widely used in highly efficient p-i-n structure single junction perovskite solar cells. While BCP buffer layer protects the underneath layers from damage, itself can be damaged by sputtering of TCOs at a wide range of target-substrate distances, supported by molecular dynamic simulation. More intriguingly, it is observed that TCO easily peeled off after sputtering when the sputtering target is close to substrate. This is ascribed to formation of stress during cooling down process after sputtering due to different thermal expansion coefficients of the layers. Our studies explain why tin oxide (SnO2) made by atomic layer deposition can replace BCP for a much better tandem device performance. SnO2 has high affinity with sputtered TCO electrode to suppress peeling-off issue and has higher bond energy to resist sputter induced damage, thus it allows a wider window of target-substrate distances than BCP during TCO sputtering. Ultimately, we demonstrate an efficient perovskite/silicon monolithic tandem solar cell with efficiency of 26.0% to illustrate the beneficial effects of reduced stress and damage.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Over 31% efficient indoor organic photovoltaics enabled by simultaneously reduced trap-assisted recombination and non-radiative recombination voltage loss

Indoor organic photovoltaics (OPVs) have shown great potential application in driving low-energy-consumption electronics for the Internet of Things. There is still great room for further improving the power conversion efficiency (PCE) of indoor OPVs, considering that the desired morphology of the active layer to reduce trap-assisted recombination and voltage losses and thus simultaneously enhance the fill factor (FF) and open-circuit voltage for efficient indoor OPVs remains obscure. Herein, by optimizing the bulk and interface morphology via a layer-by-layer (LBL) processing strategy, low leakage current and low non-radiative recombination loss can be synergistically achieved in PM6:Y6-O based devices. Detailed characterizations reveal the stronger crystallinity, purer domains and ideal interfacial contacts in the LBL devices compared to their bulk-heterojunction (BHJ) counterparts. The optimized morphology yields a reduced voltage loss and an impressive FF of 81.5%, and thus contributes to a high PCE of 31.2% under a 1000 lux light-emitting diode (LED) illumination in the LBL devices, which is the best reported efficiency for indoor OPVs. Additionally, this LBL strategy exhibits great universality in promoting the performance of indoor OPVs, as exemplified by three other non-fullerene acceptor systems. Finally, this work provides guidelines for morphology optimization and synergistically promotes the fast development of efficient indoor OPVs.

36 MATERIALS SCIENCE↗