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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 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Intrinsically stable organic solar cells under high-intensity illumination

Organic photovoltaic cells are now approaching commercially viable efficiencies, particularly for applications that make use of their unique potential for flexibility and semitransparency. However, their reliability remains a major concern, as even the most stable devices reported so far degrade within only a few years. This has led to the belief that short operational lifetimes are an intrinsic disadvantage of devices that are fabricated using weakly bonded organic materials—an idea that persists despite the rapid growth and acceptance of organic light-emitting devices, which can achieve lifetimes of several million hours9. Here we study an extremely stable class of thermally evaporated single-junction organic photovoltaic cells. We accelerated the aging process by exposing the packaged cells to white-light illumination intensities of up to 37 Suns. The cells maintained more than 87 percent of their starting efficiency after exposure for more than 68 days. The degradation rate increases superlinearly with intensity, leading to an extrapolated intrinsic lifetime, T 80 , of more than 4.9 × 10 7 hours, where T 80 is the time taken for the power conversion efficiency to decrease to 80 per cent of its initial value. This is equivalent to 27,000 years outdoors. Additionally, we subjected a second group of organic photovoltaic cells to 20 Suns of ultraviolet illumination (centred at 365 nanometres) for 848 hours, a dose that would take 1.7 × 10 4 hours (9.3 years) to accumulate outdoors. No efficiency loss was observed over the duration of the test. Overall, we find that organic solar cells packaged in an inert atmosphere can be extremely stable, which is promising for their future use as a practical energy generation technology.

14 SOLAR ENERGY↗
DOE OSTI2015

Watching the dynamics of electrons and atoms at work in solar energy conversion

The photochemical reactions performed by transition metal complexes have been proposed as viable routes towards solar energy conversion and storage into other forms that can be conveniently used in our everyday applications. In order to develop efficient materials, it is necessary to identify, characterize and optimize the elementary steps of the entire process on the atomic scale. To this end, we have studied the photoinduced electronic and structural dynamics in two heterobimetallic ruthenium–cobalt dyads, which belong to the large family of donor–bridge–acceptor systems. Using a combination of ultrafast optical and X-ray absorption spectroscopies, we can clock the light-driven electron transfer processes with element and spin sensitivity. In addition, the changes in local structure around the two metal centers are monitored. These experiments show that the nature of the connecting bridge is decisive for controlling the forward and the backward electron transfer rates, a result supported by quantum chemistry calculations. More generally, this work illustrates how ultrafast optical and X-ray techniques can disentangle the influence of spin, electronic and nuclear factors on the intramolecular electron transfer process. Finally, some implications for further improving the design of bridged sensitizer-catalysts utilizing the presented methodology are outlined.

14 SOLAR ENERGY↗
DOE OSTI2013

ON THE REMOTE DETECTION OF SUPRATHERMAL IONS IN THE SOLAR CORONA AND THEIR ROLE AS SEEDS FOR SOLAR ENERGETIC PARTICLE PRODUCTION

Forecasting large solar energetic particle (SEP) events associated with shocks driven by fast coronal mass ejections (CMEs) poses a major difficulty in the field of space weather. Besides issues associated with CME initiation, the SEP intensities are difficult to predict, spanning three orders of magnitude at any given CME speed. Many lines of indirect evidence point to the pre-existence of suprathermal seed particles for injection into the acceleration process as a key ingredient limiting the SEP intensity of a given event. This paper outlines the observational and theoretical basis for the inference that a suprathermal particle population is present prior to large SEP events, explores various scenarios for generating seed particles and their observational signatures, and explains how such suprathermals could be detected through measuring the wings of the H I Ly{alpha} line.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

SOLAR FLARE ELEMENT ABUNDANCES FROM THE SOLAR ASSEMBLY FOR X-RAYS (SAX) ON MESSENGER

X-ray spectra in the range 1.5–8.5 keV have been analyzed for 526 large flares detected with the Solar Assembly for X-rays (SAX) on the Mercury MESSENGER spacecraft between 2007 and 2013. For each flare, the temperature and emission measure of the emitting plasma were determined from the spectrum of the continuum. In addition, with the SAX energy resolution of 0.6 keV (FWHM) at 6 keV, the intensities of the clearly resolved Fe-line complex at 6.7 keV and the Ca-line complex at 3.9 keV were determined, along with those of unresolved line complexes from S, Si, and Ar at lower energies. Comparisons of these line intensities with theoretical spectra allow the abundances of these elements relative to hydrogen to be derived, with uncertainties due to instrument calibration and the unknown temperature distribution of the emitting plasma. While significant deviations are found for the abundances of Fe and Ca from flare to flare, the abundances averaged over all flares are found to be enhanced over photospheric values by factors of 1.66 ± 0.34 (Fe), 3.89 ± 0.76 (Ca), 1.23 ± 0.45 (S), 1.64 ± 0.66 (Si), and 2.48 ± 0.90 (Ar). These factors differ from previous reported values for Fe and Si at least. They suggest a more complex relation of abundance enhancement with the first ionization potential (FIP) of the element than previously considered, with the possibility that fractionation occurs in flares for elements with an FIP of less than ∼7 eV rather than ∼10 eV.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Evaluating transition metal oxides within DFT-SCAN and SCAN + U frameworks for solar thermochemical applications

Using the strongly constrained and appropriately normed (SCAN) and SCAN+U approximations for describing electron exchange-correlation (XC) within density functional theory, we investigate the oxidation energetics, lattice constants, and electronic structure of binary Ce-, Mn-, and Fe-oxides, which are crucial ingredients for generating renewable fuels using two-step, oxide-based, solar thermochemical reactors. Unlike other common XC functionals, we find that SCAN does not over-bind the O 2 molecule, based on direct calculations of its bond energy and robust agreement between calculated formation enthalpies of main group oxides versus experiments. However, in the case of transition-metal oxides (TMOs), SCAN systematically overestimates (i.e., yields too negative) oxidation enthalpies due to remaining self-interaction errors in the description of their ground-state electronic structure. Adding a Hubbard U term to the transition-metal centers, where the magnitude of U is determined from experimental oxidation enthalpies, significantly improves the qualitative agreement and marginally improves the quantitative agreement of SCAN+U-calculated electronic structure and lattice parameters, respectively, with experiments. Importantly, SCAN predicts the wrong ground-state structure for a few oxides, namely, Ce 2 O 3 , Mn 2 O 3 , and Fe 3 O 4 , while SCAN+U predicts the right polymorph for all systems considered in this work. Furthermore, the SCAN+U framework, with an appropriately determined U, will be required to accurately describe ground-state properties and yield qualitatively consistent electronic properties for most transition-metal and rare earth oxides.

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

Solar-Thermal Ammonia Production: A Renewable, Carbon-Neutral Route to Ammonia via Concentrating Solar Thermochemistry [Slides]

Solar Thermal Ammonia Production has potential to produce green ammonia using CSP, air, and water. Air separation to purify N 2 was successfully demonstrated with BSF1585 in packed bed reactor; on-sun reduction reactor under construction. Metal nitrides (MNy) were successfully synthesized and characterized under both ambient and pressurized conditions. Co 3 Mo 3 N shown to successfully produce NH 3 when exposed to pure H 2 at pressures between 5 – 20 bar 600 – 750 °C. Ambient reaction experiments imply there may be a catalytic aspect as well. Technoeconomic and systems analyses show a path towards scale-up.

14 SOLAR ENERGY↗
DOE OSTI2026

Identifying Barriers to Solar and Storage Hybrids: Modeled vs. empirical wholesale market value and net-value for co-located solar + storage projects [Slides]

Large-scale (1MW+) co-located solar and battery storage projects are expanding rapidly in the United States, but their realized contribution to the bulk power system remains poorly understood because public project-level operating data are limited. The Lawrence Berkeley National Laboratory estimates the wholesale market value of 280 operational photovoltaic-plus-storage (PV+S) projects across the seven ISOs/RTOs and 19 additional balancing authorities, representing roughly 95% of the U.S. PV+S fleet in 2024. We model optimized hourly dispatch under energy, capacity, and ancillary-service market opportunities and compare the resulting value with standalone PV value, project-specific levelized cost estimates, and empirical operating or revenue data where available.

14 SOLAR ENERGY↗