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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Thermionic Energy Conversion (TEC) topping thermoelectrics

Performance expectations for thermionic and thermoelectric energy conversion systems are reviewed. It is noted that internal radiation effects diminish thermoelectric figures of merit significantly at 1000 K and substantially at 2000 K; the effective thermal conductivity contribution of intrathermoelectric radiative dissipation increases with the third power of temperature. It is argued that a consideration of thermoelectric power generation with high temperature heat sources should include utilization of thermionic energy conversion (TEC) topping thermoelectrics. However TEC alone or TEC topping more efficient conversion systems like steam or gas turbines, combined cycles, or Stirling engines would be more desirable generally.

Morris, J. F.↗
NASA NTRS1983

Energy conversion for megawatt space power systems

Large nuclear space power systems capable of continuously producing over one megawatt of electrical power for a several year period will be needed in the future. This paper presents the results of a study to compare applicable conversion technologies which were deemed to be ready for a time period of 1995 and beyond. A total of six different conversion technologies were studied in detail and compared on the basis of conversion efficiency, radiator area, overall system mass, and feasibility. Three static, modular conversion technologies were considered; these include: AMTEC, thermionic, and thermoelectric conversion. The other three conversion technologies are heat engines which involve dynamic components. The dynamic systems analyzed were Brayton, Rankine, and the free piston Stirling engine. Each of the conversion techniques was also examined for limiting characteristics and an attempt was made to identify common research needs and enabling technologies.

Ewell, R.↗
NASA NTRS1984

Towards a 20 percent efficient silicon solar cell

A project is underway at the University of New South Wales aimed at producing a 20 percent efficient silicon solar cell. A prerequisite for obtaining such a significant increase in cell efficiency is the improvement of the open circuit voltage of these cells. Two techniques are described which have produced experimental devices with open circuit voltages of 690 mV or higher. These high voltage techniques have been combined with other high efficiency design features to produce silicon cells with independently measured energy conversion efficiencies in excess of 19 percent under standard terrestrial test conditions (direct beam AM1.5 spectrum, 100 mW/sq cm, 28 C).

Green, M. A.↗
NASA NTRS1989

Photochemistry of the atmosphere of Uranus

A detailed one-dimensional photochemical model incorporating vertical transport by eddy and molecular diffusion is used to study the importance of chemical and physical processes that control the hydrocarbon abundances in the stratosphere of Uranus. The study includes updated photochemical reaction rates and photolysis branching ratios; explicit calculation of the condensation rate of condensing species; and appropriate boundary conditions at the tropopause. It is found that the basic photochemical process generally produces low net conversion efficiencies of methane to higher hydrocarbons. However, even with these low efficiencies, the total condensation rate, which represents the net rate of conversion of methane to hydrocarbons, is roughly 2 x 10 to the -16th g/cm sec, in agreement with the upper range of the low condensation rate for the production of the stratospheric aerosol layer as determined by Pollack et al. (1987). Furthermore, a range of vertical transport rates is required to separately match the observational constraints on hydrocarbon abundances. The solar reflection data refer to the sunlit polar region of Uranus and require an eddy diffusion coefficient of K approx. = 50 sq cm/sec for globally averaged insolation or K approx = 1500 (Nh/N) exp 1/2 for overhead sun. The Voyager 2 Utraviolet Spectrometer solar occultation data refer to the equatorial regions, thus implying a large latitudinal gradient in stratospheric hydrocarbon abundance.

Summers, Michael E.↗
NASA NTRS2006

Power Budget Analysis for High Altitude Airships

The High Altitude Airship (HAA) has various potential applications and mission scenarios that require onboard energy harvesting and power distribution systems. The energy source considered for the HAA s power budget is solar photon energy that allows the use of either photovoltaic (PV) cells or advanced thermoelectric (ATE) converters. Both PV cells and an ATE system utilizing high performance thermoelectric materials were briefly compared to identify the advantages of ATE for HAA applications in this study. The ATE can generate a higher quantity of harvested energy than PV cells by utilizing the cascaded efficiency of a three-staged ATE in a tandem mode configuration. Assuming that each stage of ATE material has the figure of merit of 5, the cascaded efficiency of a three-staged ATE system approaches the overall conversion efficiency greater than 60%. Based on this estimated efficiency, the configuration of a HAA and the power utility modules are defined.

Choi, Sang H.↗
NASA NTRS2024

A Perspective on Multi-Source Energy Harvesting Technology Using Piezoelectric and Thermoelectric Materials

Energy harvesting using various locally available energy sources such as vibration energy, heat, sound, or magnetic field have become attractive topics for supplying power to modular electronic devices making them run independently in extreme environments. In this paper, we will be discussing the perspectives on thermoelectric (TE) and piezoelectric materials and devices, and then the concept of multi-source energy harvester using piezoelectric and thermoelectric devices and integration of them into a reliable and independent power source. TE materials having low thermal conductivity and high figure-of-merit ( zT ) are developed to convert even a small temperature gradient efficiently into electrical energy with the state-of-the-art conversion efficiency of ~15% and output power of ~56 W from single device. The piezoelectric device architecture is configured using high performance piezoelectric ceramics (Cu-Mn-PIN-PMN-PT). These ceramics exhibit high piezoelectric coefficient with high mechanical quality factor and low dielectric loss factor. Using these piezoelectric materials, power density as high a 2 mW/cm 2 is demonstrated in 1-1.5 g vibration environments. The piezoelectric device is attached on the surface of TE module to capture both the vibration and thermal energy sources to realize dual mode energy harvester. The multi-energy transfer strategy opens opportunities for a future generation of wireless and modular electronic devices. These devices would be useful in powering wearable electronic devices, micro sensor chargers, etc. in extreme environmental conditions using body heat/thermal sources and induced motion/vibrations.

Piezoelectric↗
DOE OSTI2020

Thin-Film Solar Cells with 19% Efficiency by Thermal Evaporation of CdSe and CdTe

CdTe-based solar cells exhibiting 19% power conversion efficiency were produced using widely available thermal evaporation deposition of the absorber layers on SnO2-coated glass with or without a transparent MgZnO buffer layer. Evaporating CdSe and CdTe sequentially by thermal evaporation and subsequent CdCl2 annealing establishes efffective CdSeTe band grading as well as dense, large-grain films. These results show that high-performance II-VI photovoltaics can be made by inexpensive, commercially available evaporation systems without the need to build customized equipment, enabling CdTe photovoltaics research and manufacturing to be more accessible to the broader photovoltaics community.

14 SOLAR ENERGY↗
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 OSTI2023

Scalable Manufacturing of Efficient Perovskite/Silicon Tandem Modules

Crystalline-Si (c-Si) technology produces excellent solar cells with conversion efficiencies of up to 26.7%—nearly their practical limit of 27%—and has been commercialized extensively to produce panels below $\$0.40$/W. Techno-economic analysis shows that module efficiency will continue to be a primary cost driver because of high balance-ofsystems costs, and there is no path to higher efficiencies with single-junction silicon cells. In this project, three research teams from University of North Carolina, Arizona State University and National Renewable National Laboratory worked together to develop perovskite-silicon tandem cells with a high throughput process which can handle 5000 wafers per hour, enabled by very low added CAPEX of ~$20k for a doctor-blade coater. This can potentially increase the module efficiency to 30% (with grid) with small increase of cost, which will drive down the cost of silicon modules to be at least 16% cheaper than present silicon PERC modules. We also explored the alternative narrow bandgap perovskites as silicon replacement for all perovskite tandem cells. This project has substantially advanced the progress of solution-process perovskitessilicon tandem solar cells and perovskite-perovskite tandem solar cells with many inventions and discoveries, evidenced by 18 publications and 6 invention disclosures. Several notable examples include 1) we developed the new idea of small pyramid in combination with solution grown perovskites and demonstrated record-efficiency of 28.5% for 1 cm2 on textured silicon bottom cells and 25.2% for 24 cm2 on chemically etched silicon bottom cells for perovskite-silicon tandem cells. 2) We developed perovskite ink that can coat perovskites onto texture silicon without voids;, and new device structure to enhance the yield of fabrication by reducing shunting 3) We identified the origin of open circuit voltage on mixed halide wide bandgap perovskites, and came with a solution for this problem, reducing the voltage loss to a record small value, which can potentially push the perovskite-silicon tandem cell efficiency to over 31%; 4) We have developed efficient alternative low bandgap semiconductors, i.e. gradient-doped Sn based perovskites by Ba ions, new oxide hole transport layers which increase the efficiency of perovskite/perovskite tandem cells reached record efficiency of 26.3%; 5) We developed bifacial perovskite/perovskite tandem cells by overcoming contacts issues and regaining light absorption, further boosting the equivalent efficiency to 29.3% under 1 sun illumination with 30% albedo light; 6) We developed the first all perovskite tandem module fabricated in air by discovery a combination of oxidization and reduction couples, yield an aperture efficiency of 21.6% for all perovskite mininodules, exceeding that of single junction perovskite minimodules. These discoveries not only accelerate the commercialization of perovskite-silicon tandem solar cells, but also provide guidance in designing other type of perovskite solar cell technologies.

14 SOLAR ENERGY↗
NASA NTRS1985

Processing technology for high efficiency silicon solar cells

Recent advances in silicon solar cell processing have led to attainment of conversion efficiency approaching 20%. The basic cell design is investigated and features of greatest importance to achievement of 20% efficiency are indicated. Experiments to separately optimize high efficiency design features in test structures are discussed. The integration of these features in a high efficiency cell is examined. Ion implantation has been used to achieve optimal concentrations of emitter dopant and junction depth. The optimization reflects the trade-off between high sheet conductivity, necessary for high fill factor, and heavy doping effects, which must be minimized for high open circuit voltage. A second important aspect of the design experiments is the development of a passivation process to minimize front surface recombination velocity. The manner in which a thin SiO2 layer may be used for this purpose is indicated without increasing reflection losses, if the antireflection coating is properly designed. Details are presented of processing intended to reduce recombination at the contact/Si interface. Data on cell performance (including CZ and ribbon) and analysis of loss mechanisms are also presented.

Spitzer, M. B.↗
DOE OSTI2022

High-efficiency microwave-optical quantum transduction based on a cavity electro-optic superconducting system with long coherence time

Abstract Frequency conversion between microwave and optical photons is a key enabling technology to create links between superconducting quantum processors and to realize distributed quantum networks. We propose a microwave-optical transduction platform based on long-coherence time superconducting radio-frequency (SRF) cavities coupled to electro-optic optical cavities to mitigate the loss mechanisms that limit the attainment of high conversion efficiency. We optimize the microwave-optical field overlap and optical coupling losses in the design while achieving long microwave and optical photon lifetime at milli-Kelvin temperatures. This represents a significant enhancement of the transduction efficiency up to 50% under incoming pump power of 140 μW, which allows the conversion of few-photon quantum signals. Furthermore, this scheme exhibits high resolution for optically reading out the dispersive shift induced by a superconducting transmon qubit coupled to the SRF cavity. We also show that low microwave losses enhance the fidelity of heralded entanglement generation between two remote quantum systems. Finally, high precision in quantum sensing can be reached below the standard quantum limit.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Chemical Design of Organic Interface Modifiers for Highly Efficient and Stable Perovskite Solar Cells

Perovskite solar cells (PSCs) have demonstrated rapid progress in their power conversion efficiencies (PCEs) - from 3.8% in 2009 to 25.7% in 2022 - and they have received considerable attention as a promising future photovoltaic (PV) technology. However, the operational stability of PSCs is still inadequate to satisfy the standards for commercial applications. Interface engineering has become one of the most important strategies to push PSCs' efficiency and stability for practical use. Among the various interface engineering approaches, organic interface modifiers (OIMs) have been frequently used by the PSC field to address the issues limiting PSC stability at high efficiency levels. In this perspective, the chemical structures of state-of-the-art OIMs are discussed, and their characteristics are reviewed, as well as the impact on device performance associated with key device interfaces (e.g., metal oxide/perovskite and organic transport layer/perovskite interfaces) from a chemical and materials engineering point of view is discussed. Finally, design considerations and the authors' perspective are discussed, on the basis of representative literature examples, for building new, customized organic OIMs to further improve PSC efficiency and stability toward commercialization.

14 SOLAR ENERGY↗
DOE OSTI2020

Efficient, stable silicon tandem cells enabled by anion-engineered wide-bandgap perovskites

Maximizing the power conversion efficiency (PCE) of perovskite/silicon tandem solar cells that can exceed the Shockley-Queisser single-cell limit requires a high-performing, stable perovskite top cell with a wide bandgap. We developed a stable perovskite solar cell with a bandgap of ~1.7 electron volts that retained more than 80% of its initial PCE of 20.7% after 1000 hours of continuous illumination. Anion engineering of phenethylammonium-based two-dimensional (2D) additives was critical for controlling the structural and electrical properties of the 2D passivation layers based on a lead iodide framework. The high PCE of 26.7% of a monolithic two-terminal wide-bandgap perovskite/silicon tandem solar cell was made possible by the ideal combination of spectral responses of the top and bottom cells.

14 SOLAR ENERGY↗
NASA NTRS1974

Design, construction and evaluation of a 12.2 GHz, 4.0 kW-CW high efficiency klystron amplifier

An analytical and experimental program is described, for studying design techniques for optimizing the conversion efficiency of klystron amplifiers, and to utilize these techniques in the development and fabrication of an X-band 4 kW cw klystron, for use in satellite-borne television broadcast transmitters. The design is based on a technique for increasing the RF beam current by using the second harmonic space charge forces in the bunched beam. Experimental analysis was also made of a method to enhance circuit efficiency in the klystron cavities. The design incorporates a collector which is demountable from the tube to facilitate multistage depressed collector experiments employing an axisymmetric, electrostatic collector for linear beam microwave tubes.

Vishida, J. M.↗
DOE OSTI2022

Titanium Carbide MXene Hole Contacts for CdTe Photovoltaics

CdTe is a high‐efficiency thin‐film photovoltaic technology that has seen tremendous commercial success over the past decade. Yet despite the improvement of other device characteristics, the fabrication of an ohmic hole back contact layer has remained a challenge due to the high ionization potential of CdTe, which limits the external potential that can be feasibly reached even as other characteristics of the device improve. MXenes, a family of 2D materials with rapidly growing scientific and commercial interest, offer a promising route to forming low‐cost, low‐barrier contacts due to their demonstrated high work function, metallic conductivity, and facile solution processing from benign solvents. Here, it is shown that Ti 3 C 2 T x MXene films processed from an aqueous colloidal dispersion can perform as a highly efficient hole contact material for CdTe solar cells, resulting in high power‐conversion efficiencies. The role of the Schottky barrier formation in Ti 3 C 2 T x ‐contacted CdTe devices is probed, and potential pathways for the future development of this potent combination of materials are elucidated. The modularity of the expansive MXene family of materials presents a promising strategy for developing next‐generation hole contacts for CdTe solar cells.

14 SOLAR ENERGY↗
DOE OSTI2024

Photon management in silicon photovoltaic cells: A critical review

With the practical efficiency of the silicon photovoltaic (PV) cell approaching its theoretical limit, pushing conversion efficiencies even higher now relies on reducing every type of power loss that can occur within the device. Limiting optical losses is therefore critical and requires effective management of incident photons in terms of how they interact with the device. Ultimately, photon management within a PV cell means engineering the device and constituent materials to maximize photon absorption within the active semiconductor and therefore reduce the number of photons lost through other means, most notably reflection and parasitic absorption. There have been great advancements in the front and the rear side photon management techniques in recent years. This review aims to discuss these advancements and compare the various approaches, not only in terms of increases in photogenerated current, but also their compatibility with different PV cell architectures and potential trade-offs, like increased surface recombination or scalability for high-volume manufacturing. In this review, a comprehensive discussion of a wide variety of the front and the rear side photon management structures are presented with suggestions to improve the already achieved performance further. Here, this review is unique because it not only presents the recent development in photon management techniques, but also offers through analysis of these techniques and pathways to improve further.

14 SOLAR ENERGY↗
DOE OSTI2020

Scalable fabrication and coating methods for perovskite solar cells and solar modules

Since the report in 2012 of a solid-state perovskite solar cell (PSC) with a power-conversion efficiency (PCE) of 9.7% and a stability of 500 h, intensive efforts have been made to increase the certified PCE, reaching 25.2% in 2019. The PCE of PSCs now exceeds that of conventional thin-film solar-cell technologies, and the rate at which this increase has been achieved is unprecedented in the history of photovoltaics. Moreover, the development of moisture-stable and heat-stable materials has increased the stability of PSCs. Small-area devices (<1 cm2) are typically fabricated using a spin-coating method; however, this approach may not be suitable for the preparation of the large-area (>100 cm2) substrates required for commercialization. Thus, materials and methods need to be developed for coating large-area PSCs. In this Review, we discuss solution-based and vapour-phase coating methods for the fabrication of large-area perovskite films, examine the progress in performance and the parameters affecting the properties of large-area coatings, and provide an overview of the methodologies for achieving high-efficiency perovskite solar modules.

14 SOLAR ENERGY↗