SEARCH · Search NASA

Results for “open circuit”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8

All sources NASA NTRS DOE OSTI

DOE OSTI2020

Electrothermal Phenomena in Ferroelectrics

Physical properties of lead-zirconate-titanate (PZT) ceramics change according to the initial electric poling process and electrical boundary conditions. This paper reports the electrothermal, piezothermal, and piezoelectric coupling phenomena in ferroelectrics from thermodynamics viewpoints, in particular, thermal property differences between unpoled and poled PZT’s in the poling direction for open circuit and short circuit conditions. We propose a new terminology, “secondary electrothermal” coupling factor kλ, which is analogous to the electromechanical coupling factor k, relating the elastic compliances under short- and open-circuit conditions, in order to explain the fact that the short-circuit condition exhibited the larger thermal diffusivity than the open-circuit condition. On the other hand, the unpoled specimen exhibits the lowest thermal diffusivity. This tutorial paper was authored for providing comprehensive knowledge on equilibrium and time-dependent thermodynamics in ferroelectrics.

Uchino, Kenji (ORCID:0000000316517912)↗

DOE OSTI2021

Evaluating capacity fade in dual insertion batteries using potential and temperature measurements

Methods and systems are described of managing a battery system. The battery system including at least one battery cell and one or more sensors configured to measure a temperature of the at least one battery cell. The method includes receiving a measurement of the temperature of the at least one battery cell, estimating an open circuit potential of the at least one battery cell, estimating a capacity fade of the at least one battery cell based on the open circuit potential of the at least one battery cell and a ratio of a change in the open circuit potential relative to a change in the temperature of the at least one battery cell, and regulating at least one of charging or discharging of the at least one battery cell based on the estimation of the capacity fade.

Christensen, John F.↗

DOE OSTI2025

Tracking Spatiotemporal Electric Potential in Batteries Using High-Resolution Operando X‑ray Transmission Imaging

The formation of significant concentration gradients across electrolytes in batteries affects the rate at which electrochemical reactions occur. In this work, we use high-resolution operando X-ray transmission imaging to capture spatiotemporal salt concentration profiles c(x,t) in a symmetric cell comprising a polymer electrolyte sandwiched between two lithium–indium alloy electrodes during a constant-current experiment followed by open-circuit relaxation. The decay of open-circuit potential is related to the concentration dependence of the potential across concentration cells, U. We show how operando c(x,t) data can be used to calculate the spatiotemporal electric potential “inside” the polarized electrolyte. We track the spatial- and time-dependent cell potential during the constant-current step and distinguish its two contributions: a concentration overpotential governed by U. and an ohmic contribution governed by ionic conductivity. Over most of the time window, the concentration overpotential dominates. At steady state, it is a factor of 7 larger than the ohmic contribution. Such findings indicate that efforts to design new polymer electrolytes should focus on minimizing concentration gradients.

Electrical conductivity↗

NASA NTRS1973

Design, fabrication and characteristics of new types of back surface field cells

Several new types of back surface field (BSF) cells were designed and fabricated. These include boron and phosphorus diffused BSF cells, single crystal epitaxially grown BSF cells and chemically vapor deposited (CVD) polycrystalline BSF cells. Boron diffusion yielded 10 ohm-cm BSF cells with 0.6 volt open-circuit voltages and collection efficiencies equal to those previously reported for aluminum alloying. The epitaxially grown cells also exhibited high open-circuit voltages and collection efficiencies and may be more radiation damage resistant. The polycrystalline cells had very high internal series resistance. No direct relationship was found to exist between collection efficiency and open-circuit voltage, V sub oc in BSF cells. Results indicate that the V sub oc effect is not caused simply by the mechanism of blocking of minority carriers.

Mandelkorn, J.↗

NASA NTRS1974

Design, fabrication and characteristics of new types of back surface field cells

Mandelkorn, J.↗

DOE OSTI2025

Redox Couples Control Band Bending, Photovoltage, and Quasi-Fermi Levels in Tungsten Oxide (WO 3 ) Photoanodes

Tungsten oxide (WO 3 ) is a well-known photoanode and photocatalyst for photoelectrochemical (PEC) water oxidation. Because the compound has a deep valence band, it can facilitate the oxygen evolution reaction without added cocatalysts, and it can drive the oxidation of species with much higher electrochemical potentials, including the conversion of water to hydrogen peroxide, sulfate to persulfate, and iodate to meta-periodate. Here, we use the liquid vibrating Kelvin probe surface photovoltage (liquid VK-SPV) technique in combination with open circuit potential (OCP) and photoelectrochemical (PEC) scans to assess the possibility of reaching such oxidizing potentials in aqueous electrolytes and at open circuit. Here, this is done by mapping the quasi-Fermi levels of electrons and holes at the interfaces as a function of the light intensity. Nanostructured WO 3 photoelectrodes for this purpose were fabricated by thermal annealing of a tungstic acid solution on fluorine-doped tin oxide. Electrochemical measurements are conducted at open circuit and 400 nm LED light illumination in electrolytes containing fast (O 2 /H 2 O 2 ), slow (O 2 /H 2 O), and very oxidizing (NaIO 4 /NaIO 3 ) redox couples. Photovoltage values scale with the light intensity and with the built-in potential for each redox couple and reach values up to 0.61 V under 20 mW cm –2 illumination for the NaIO 4 electrolyte. This shows that the photoelectrodes behave like Schottky-type diodes whose maximum possible energy output is determined mainly by the built-in voltage of each junction. For slow redox couples, the quasi-Fermi level of the holes increases with light intensity due to hole accumulation at the WO 3 –liquid interface. For example, for the O 2 /H 2 O electrolyte, interfacial hole accumulation and removal occur on the 90–300 s time scale. For the fast hole acceptor H 2 O 2 , on the other hand, the quasi-Fermi level of the photoholes is pinned to the electrochemical potential of the O 2 /H 2 O 2 couple. This limits the energy conversion efficiency of the electrode. Overall, these results reveal the influence of charge transfer thermodynamics and kinetics on the photovoltage of WO 3 . Furthermore, the work further establishes VK-SPV as a contactless method to observe the photovoltage, carrier dynamics, and quasi-Fermi levels of semiconductor-liquid junctions.

Electrodes↗

NASA NTRS1981

Thermal stability of GaAs heteroface solar cells with differing contact materials

GaAlAs/GaAs heteroface solar cells used in space offer advantages of higher operating temperatures and recovery from radiation damage using thermal annealing. Elevated temperature experiments were conducted to evaluate the electrical stability of cells with different contact materials. These experiments indicate that for operation of GaAs heteroface solar cells at elevated temperatures, front contact metals must be carefully chosen. The short circuit current varied by only about 3% for cells with Pd/Ag contacts that were heated to 240 C for a total of 500 hours. However, a total decrease in the open circuit voltage of about 20% was observed for these cells. After heating cells to 400 C, large changes in open circuit voltage were observed for cells with Pd/Ag, Pd/Au, Pd, Ag, and Ti contacts; however, preliminary results indicate more stable open circuit voltages for cells with Au, Cr, Zn, and Cr/Au contacts.

Friesen, W. J.↗

NASA NTRS1984

Mechanisms limiting the performance of large grain polycrystalline silicon solar cells

The open-circuit voltage and short-circuit current of large-grain (1 to 10 mm grain diameter) polycrystalline silicon solar cells is determined by the minority-carrier diffusion length within the bulk of the grains. This was demonstrated by irradiating polycrystalline and single-crystal (Czochralski) silicon solar cells with 1 MeV electrons to reduce their bulk lifetime. The variation of short-circuit current with minority-carrier diffusion length for the polycrystalline solar cells is identical to that of the single-crystal solar cells. The open-circuit voltage versus short-circuit current characteristic of the polycrystalline solar cells for reduced diffusion lengths is also identical to that of the single-crystal solar cells. The open-circuit voltage of the polycrystalline solar cells is a strong function of quasi-neutral (bulk) recombination, and is reduced only slightly, if at all, by grain-boundary recombination.

Culik, J. S.↗

NASA NTRS1979

Radiation damage in high-voltage silicon solar cells

Three types of open circuit high voltage solar cells were tested to determine their performance after exposure to 1 MeV electron irradiations. The cells with a relatively deep n-type emitter were more susceptible to radiation damage than other high open circuit high voltage cells. The use of diffused or ion implanted junctions leads to open circuit high voltage cell designs that are less susceptible to radiation damage. These latter two types of cells show degradations that are typical of the 0.1 ohm-cm material from which they are fabricated. Furthermore, exposure to ionizing radiation causes oxide degradation and decreased cell performance in cells that depend on a charged oxide to achieve significant cell properties. Hence, the combination of a charged oxide and a relatively deep n-type emitter is not recommended for incorporation into a cell designed for use in the particulate radiation environment of space.

Weinberg, I.↗

NASA NTRS1984

Process Research on Polycrystalline Silicon Material (PROPSM)

Results of hydrogen-passivated polycrystalline silicon solar cells are summarized. Very small grain or short minority-carrier diffusion length silicon was used. Hydrogenated solar cells fabricated from this material appear to have effective minority-carrier diffusion lengths that are still not very long, as shown by the open-circuit voltages of passivated cells that are still significantly less than those of single-crystal solar cells. The short-circuit current of solar cells fabricated from large-grain cast polycrystalline silicon is nearly equivalent to that of single-crystal cells, which indicates long bulk minority-carrier diffusion length. However, the open-circuit voltage, which is sensitive to grain boundary recombination, is sometimes 20 to 40 mV less. The goal was to minimize variations in open-circuit voltage and fill-factor caused by defects by passivating these defects using a hydrogenation process. Treatments with molecular hydrogen showed no effect on large-grain cast polycrystaline silicon solar cells.

Culik, J. S.↗

NASA NTRS1982

Towards a 700 mV silicon solar cell

The key to improved silicon solar cell performance lies in increasing cell open circuit voltage. Not only does improved voltage direclty increase cell efficiency, but it also increases the limiting value of fill factor and decreases the temperature sensitivity of the cell. Limits on attainable open circuit voltage are not well defined. A thermodynamic limit of 850 mV exists for black body silicon cells, with 700 mV long regarded as a practical limit. This paper describes experimental work which has resulted in experimental devices with open circuit voltages approaching 700 mV. Values up to 694 (AM0, 25 C) have been demonstrated. The cells are similar in structure to conventional p-n junction cells, but particular attention is paid to passivating the entire top surface of the cell, including regions under the top contact.

Green, M. A.↗

DOE OSTI2024

Control, Fault Management, and Grid Support Functionality of an MV AC-DC Solid State Transformer based EV Extreme Fast Charging Station

Electric vehicles (EVs) have become increasingly popular in recent times while revolutionizing the consumer and commercial transportation market. The development of charging infrastructure has become one of the priorities for increasing the adoption of EVs. Extreme fast charging (XFC) technology can reduce the so-called ’range anxiety’ of consumers as they significantly reduce the charging time. With the advent of wide band-gap (WBG) power devices and improvement in power electronic converters, medium voltage (MV) solid state transformer (SST) based XFC system has the potential to replace the traditional XFC stations because of the lower footprint, ease of installation, enhanced control feature, and better system efficiency. The control system design is one of the critical aspects of the SST development process. Careful consideration and detailed analysis are required to find out suitable control method for the SST based on its topology among different centralized and decentralized control architectures. Also, the control parameters selection and potential improvement to the transient response of the controller ought to be investigated. Another major concern of the SST is different types of internal fault which reduces the overall reliability of the XFC system. As a result, designing a robust protection system is essential. Among different fault modes, open circuit switch faults have received significant attention as an active research area because of their likelihood and severe effects on converters. Therefore, the power stages used in the XFC system require functional and accurate open circuit switch fault management methods. An equally significant aspect of this SST based XFC is its compatibility in a microgrid where there is no synchronous generator present. When the grid is not available, the XFC SSTs can provide grid forming capability and continue supplying the critical loads in islanded mode. The transition between grid connected and islanded mode, especially the grid resynchronization process has to be carefully performed for the safety of the microgrid components. The challenges posed by the aforementioned issues have inspired the work done in this dissertation. Here, a 13.2 kV, 1 MVA, AC/DC SST for the XFC system is examined and a comparative analysis is conducted to select the control architecture based on feasibility of implementation and performance. A detailed control parameter design process is demonstrated considering the sensor dynamics and delay. The selected decentralized control method is augmented by introducing a novel sensor-less load current feedforward method to provide better voltage regulation at the DC bus during a change of load. Next, in the fault management section, a hierarchical failure mode effect analysis (FMEA) is proposed to enable a systematic design of the internal fault protection of the XFC SST as there are limited examples in the literature regarding the analysis of the safety and design of the protection of a power electronic converter system. Novel open circuit switch fault management methods for the converters in the system are presented. Finally, XFC SST based MV microgrid operations in grid connected mode and islanded mode are explored. A secondary control method for grid resynchronization is presented and a design process of control parameters is shown to ensure the stability of the secondary voltage and frequency regulation.

30 DIRECT ENERGY CONVERSION↗

DOE OSTI2025

Predicting Trends in VOC Through Rapid, Multimodal Characterization of State-of-the-Art p-i-n Perovskite Devices

Perovskite photovoltaic technologies are approaching commercial deployment, yet single junction and tandem architectures both still have significant room to improve power conversion efficiency and stability. The ability to perform rapid screening of material quality after altering processing conditions is critical to accelerating the optimization and commercialization of perovskite-based technologies. Currently, researchers utilize a wide range of stand-alone metrology tools to isolate sources of power loss throughout a device stack, which can be slow and labor intensive. Here, we demonstrate the use of a multimodal metrology approach to rapidly determine the maximum achievable and predicted open circuit voltages of >100 perovskite devices during fabrication. Acquisition of these different data is facilitated by combining them into a single integrated measurement platform. We show that these data and automated analysis can be used to rapidly understand and ultimately predict quantitative trends in open circuit voltages of state-of-the-art device architectures. The data and automated analysis workflow presented provides a reliable approach to quickly identify absorber and charge transport layer combinations that can lead to improved open circuit voltages.

14 SOLAR ENERGY↗

NASA NTRS1980

Development of a high efficiency thin silicon solar cell

Significant improvements in open-circuit voltage and conversion efficiency, even on relatively high bulk resistivity silicon, were achieved by using a screen-printed aluminum paste back surface field. A 4 sq cm 50 micron m thick cell was fabricated from textured 10 omega-cm silicon which had an open-circuit voltage of 595 mV and AMO conversion efficiency at 25 C of 14.3%. The best 4 sq cm 50 micron thick cell (2 omega-cm silicon) produced had an open-circuit voltage of 607 mV and an AMO conversion efficiency of 15%. Processing modifications are described which resulted in better front contact integrity and reduced breakage. These modifications were utilized in the thin cell pilot line to fabricate 4 sq cm cells with an average AMO conversion efficiency at 25 C of better than 12.5% and with lot yields as great as 51% of starts; a production rate of 10,000 cells per month was demonstrated. A pilot line was operated which produced large area (25 cm) ultra-thin cells with an average AMO conversion efficiency at 25 deg of better than 11.5% and a lot yield as high as 17%.

Storti, G.↗

DOE OSTI2025

Imaging Power Losses in CdSeTe Solar Cells

Much of the research on CdSeTe photovoltaics is focused on improving the open-circuit voltage (V oc ) of the solar cell. But solar cells operate at the maximum power point (MPP) rather than at V oc . The recombination processes at MPP may be different than those at V oc , and increasing the power output at MPP is the key to advancing efficiency. Here, we introduce a camera-based PL imaging system that enables power loss analysis under operating conditions and across cm-sized areas covering multiple cells. The instrument is demonstrated with CdSeTe devices having efficiencies greater than 19%. An implied current density versus implied voltage (iJV) curve can be produced at each pixel with <20 µm resolution. We find that regions with high implied open circuit voltage are often those with low implied fill factor, showing that voltage loss analysis at open circuit is not sufficient to understand power losses under operating conditions. Measurement of JV curves as a function of irradiance can also be performed in the system, which allows series resistance-free pseudo JV (pJV) curves to be produced. Comparison of pJV to measured JV and iJV curves allows further analysis of the operational losses, pointing the way to higher efficiency.

14 SOLAR ENERGY↗

NASA NTRS1989

Effect of micrometeorid and space debris impacts on the Space Station Freedom solar array surfaces

Both solar and antisolar surfaces of the Space Station Freedom solar arrays are vulnerable to micrometeoroid and space debris impacts. Impacts on the solar surface result in damage to the active area of the solar cell and a corresponding reduction in generated power. Impacts on the antisolar surface could result in damage to the circuit which interconnects the cells which in turn may produce open circuit strings or panels. An evaluation is presented of the power degradation resulting from the impacts of micrometeoroid and space debris on the solar surface of the array blanket. Moreover, given a particle diameter that could damage the circuit interconnecting the cells, the probability of an open circuit panel is computed, along with the probability that the solar array blanket will meet the power requirement over the design lifetime.

Nahra, Henry K.↗

NASA NTRS1987

Further study of inversion layer MOS solar cells

A group of inversion layer MOS solar cells has been fabricated. The highest value of open-circuit voltage obtained for the cells is 0.568V. One of the cells has produced a short-circuit current of 79.6 mA and an open-circuit voltage of 0.54V. It is estimated that the actual area AMO efficiency of this cell is 6.6 percent with an assumed value of 0.75 for its fill factor. Efforts made for fabricating an IL/MOS cell with reasonable efficiencies are reported. Future work for 4 sq cm IL cells and 25 sq cm IL cells is discussed.

Ho, Fat Duen↗

DOE OSTI2023

Combined, time-resolved, in situ neutron reflectometry and X-ray diffraction analysis of dynamic SEI formation during electrochemical N 2 reduction

One means of improving performance for electrochemical ammonia production through the Li-mediated N 2 reduction reaction (Li-NRR) is by cycling the current driving the reaction between open-circuit conditions and periods of applied current density. Herein, we have investigated the dynamics of the electrode–electrolyte interface under Li-NRR conditions during current cycling using in situ time-resolved neutron reflectometry and grazing-incidence synchrotron X-ray diffraction. During cycling, measured neutron reflectivity curves indicated bilayer formation in which Li-containing species such as LiOH, Li 2 O, and small quantities of Li 3 N and metallic Li primarily appeared in a thin layer at the cathode surface, above which formed a much larger, porous, ‘solid–electrolyte interface’ (SEI) layer. Upon return to open-circuit conditions, Li-containing species quickly moved out of the thin layer, leaving a compact, stable layer of decomposition products underneath the SEI layer. This SEI layer concomitantly filled with electrolyte or dissolved, becoming indistinguishable from the electrolyte via contrast in scattering-length density (SLD). During the second current cycle, Li-containing species again preferentially deposited directly atop the cathode, with the thick SEI-like layer again appearing within a minute. This SEI layer exhibited a lower SLD more quickly than in the first cycle, which might suggest that Li-containing species become distributed within the porous SEI layer. Furthermore, these time-resolved observations of SEI and plated layers during current cycling suggest that benefits associated with return to open-circuit conditions between periods of applied current density may be related to the concomitant loss of Li-containing species from a thin layer at the cathode surface into a porous SEI layer that becomes filled with electrolyte or dissolves.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗