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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Damage of prismatic lithium‐ion cells subject to bending: Test, model, and detection

Abstract The mechanically induced internal short circuit (ISC) is one of the major safety concerns of lithium‐ion batteries. Mechanical abuse tests are often performed to evaluate the integrity and safety of lithium‐ion batteries under mechanical loadings. Except for the widely explored compression‐dominated indentation tests, bending is another typical real‐world loading condition that is tension‐dominated. To investigate the mechanical damage and ISC behavior of batteries under bending, we carried out controlled three‐point bending tests in four progressive steps on prismatic battery cells with maximum deflections ranging from 38% to 76% of the cell thickness. None of the tested cells experienced an ISC. We then conducted 3D X‐ray computed tomography (CT) scanning on the bent cells after unloading. X‐ray CT images showed three out of the four tested cells have extensive cracking in the electrode layers at the bottom side (opposite to the loading head). This indicates that cracking does not necessarily lead to an ISC under bending. Electrochemical impedance spectroscopy was also measured on the bent cells and substantial changes were observed. Both the bulk resistance and charge‐transfer resistance increased significantly after bending, which could influence the battery performance and lifespan. We then developed a detailed finite (FE) element model to further investigate the mechanical deformation and failure mechanisms. The FE model successfully predicts the load–displacement response and reproduces the deformation patterns. The findings and the FE model developed in the present study provide useful insights and tools for the battery structure and crash safety design. image

25 ENERGY STORAGE↗
DOE OSTI2025

Minimizing Energy Loss by Designing Multifunctional Solid Additives to Independent Regulation of Donor and Acceptor Layers for Efficient LBL Polymer Solar Cells

Solid additives are crucial in layer-by-layer (LBL) polymer solar cells (PSCs). Despite its importance, the simultaneous application of solid additives into both donor and acceptor layers has been largely overlooked. In this work, two multifunctional solid additives are actively designed, and investigated the synergistic effect on both donor and acceptor layers. Incorporating the multifunctional solid additives into the donor layer could effectively enhance the aggregation and molecular stacking of the donor polymer, leading to reduced energy disorder and minimizing ΔE 2 . When the multifunctional solid additives are introduced into the acceptor layer, they just play a role in optimizing the morphology, thereby reducing the ΔE 3 . Excitedly, the simultaneous addition of the multifunctional solid additives into both donor and acceptor layers produced a synergistic effect for decreasing ΔE 2 and ΔE 3 simultaneously, especially adding SA2, thus enabling an excellent power conversion efficiency (PCE) of 19.95% (certified as 19.68%) with an open-circuit voltage (V oc ) of 0.921 V, a short circuit current density (J sc ) of 27.08 mA cm -2 and a fill factor (FF) of 79.98%. The work highlights the potential of multifunctional solid additives in independently regulating the properties of donor and acceptor layers, which is expected as a promising approach for further developing higher performance PSCs.

36 MATERIALS SCIENCE↗
DOE OSTI2021

How Useful are Conventional I–Vs for Performance Calibration of Single- and Two-Junction Perovskite Solar Cells? A Statistical Analysis of Performance Data on ≈200 Cells from 30 Global Sources

As perovskite photovoltaics (PV) advance from the laboratory to commercial prototypes, their accurate and reliable performance testing is becoming increasingly important. The well-documented dynamic response of perovskite solar cells to an external applied voltage has led to the development of steady-state performance measurement methods; however, these methods have not been widely adopted by the perovskite PV community. A key reason for this is that steady-state measurement methods take tens of minutes to complete, as opposed to conventional "fast" current-voltage (I-V) measurements usually lasting a few seconds. Fast I-Vs arise from a snapshot, almost always not a steady-state condition of the device; however, given their widespread use, the question arises: how do performance parameters of perovskite PV compare when measured with fast I-V and with a steady-state method? Results compiled from approximately 200 perovskite PV cells, including single junction, and two-terminal perovskite-perovskite and perovskite-Si tandems, show that fast I-Vs can provide a useful measure of the open-circuit voltage of the devices, while the short-circuit current and the overall efficiency can be widely misestimated. Here, the implications of these findings on performance testing protocols are discussed and possible options for fast and accurate testing of perovskite PV are proposed.

14 SOLAR ENERGY↗
DOE OSTI2025

Monocrystalline CdSeTe/MgCdTe Double‐Heterostructure Solar Cells

This article reports monocrystalline CdSeTe/MgCdTe double‐heterostructure (DH) solar cells with varying Se compositions in the absorber layers that are grown on InSb substrates by using molecular beam epitaxy. The Se composition in the samples studied is determined to be 4%–11% through high‐resolution X‐ray diffraction (XRD) and photoluminescence measurements. Increased Se incorporation induces higher defect density attributed to increased lattice mismatch, and mixed‐phase formation due to the small difference in formation energies between the wurtzite and zinc blende phases of CdSe, which causes stacking faults and grain boundaries. Devices are fabricated by directly depositing an n‐type indium tin oxide (ITO) layer on the CdSeTe/MgCdTe DHs followed by Ag metal contacts. Reduced bandgap is observed in solar cells with increased Se composition. The devices with an absorber containing 4% Se exhibit an average open‐circuit voltage ( V OC ) of 0.925 V, a short‐circuit current density ( J SC ) of 23.4 mA/cm 2 , a fill factor ( FF ) of 0.650 and an efficiency of 14.1% without anti‐reflection coating. Absorbers with higher Se compositions result in poor device performance, mainly attributed to high defect density in the materials.

Ju, Zheng [Center for Photonics Innovation Arizona↗
DOE OSTI2021

Boosting photovoltaic performance of ternary organic solar cells by integrating a multi-functional guest acceptor

Constructing ternary structure is one of the most effective design strategies to break the efficiency ceiling of traditional binary organic solar cells (OSCs). Here, a new Y-series non-fullerene acceptor (Y-T) featuring 1,3-diethyl-2-thiobarbituric acid (DTBA) end groups is developed as a third component for the classical PM6:Y6 binary system. The champion power conversion efficiency of ternary OSCs is increased from 15.64% to 17.37% via incorporating 10 wt% Y-T, with the simultaneously enhanced open-circuit voltage (Voc) of 0.865 V, a short-circuit current density (Jsc) of 26.90 mA/cm 2 , and a fill factor (FF) of 74.97%. The positive contribution of Y-T in the ternary blend can be ascribed to the improved spectroscopic complementarity and enhanced exciton utilization ratio due to the additional energy transfer process. Moreover, Y-T guest acceptor plays a critical role in adjusting the active layer morphology and facilitating three-dimension phase separation, resulting in a balanced charge transport and enhanced FF of ternary OSCs. Overall, this work provides insight into the molecular design of non-fullerene acceptor and suggest guidelines to rationally select guest component for ternary OSCs.

14 SOLAR ENERGY↗
DOE OSTI2021

A naphthalene diimide side-chain polymer as an electron-extraction layer for stable perovskite solar cells

Poly(N-(5-(5-norbornene-2-carbonyl)oxy)pentyl)-N'-n-hexyl-naphthalene-1,8:4,5-bis(dicarboximide) has been synthesized by esterification of (N-(5-hydroxypentyl)-N'-n-hexyl-naphthalene-1,8:4,5-bis(dicarboximide)) with exo-5-norbornene-2-carboxylic acid, and has been polymerized using the first-generation Grubbs initiator. This side-chain polymer exhibits good transparency throughout the visible (absorption onset at ca. 400 nm), good solubility in common low- and medium-polarity organic solvents, good resistance to dimethylformamide, and appropriate electron affinity for use as an electron-extraction layer in lead-halide perovskite solar cells. The performance of this polymer in n-i-p perovskite solar cells was compared to that of several small-molecule naphthalene-1,8:4,5-bis(dicarboximide) derivatives and of SnO 2 . Solar cells using the polymer exhibited open-circuit voltages of up to 1.02 V, short-circuit currents of over 21 mA cm –2 , and power conversion efficiencies (PCE) reaching 14% which stabilize at 13.8% upon 90 s of illumination. Meanwhile control SnO 2 devices exhibited a PCE of ca. 16%, and small-molecule devices gave PCE values of less than 10%. Here, the devices employing the polymer exhibited improved long-term stability relative to the SnO 2 control devices under continuous illumination.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Effect of ZnO and PEDOT:PSS charge selective layers on photovoltage of cuprous oxide (Cu 2 O) heterojunction solar cells

Electrochemical deposition (ECD) of Cu 2 O provides a scalable and low temperature pathway to solar cells with a theoretical high energy conversion efficiency of 23%, based on the 2.0–2.2 eV band gap of Cu 2 O. However, existing ECD-Cu 2 O devices are plagued by poor crystallinity and low selectivity of the electron and hole transport layers. Here we use Vibrating Kelvin Probe Surface Photovoltage Spectroscopy (VKP-SPV) to probe the charge transfer selectivity in FTO/ZnO/Cu 2 O/PEDOT:PSS/Ni heterojunction solar cells. Selective electron extraction is achieved at the ZnO back contact to Cu 2 O, as confirmed by a negative surface photovoltage signal. While the uncoated Cu 2 O surface is electron-selective due to the formation of a hole depletion layer, spin coating of a PEDOT:PSS film turns it into a hole-selective interface. After adding nickel metal ink top electrodes, functional 1.0 cm 2 solar cells with power conversion efficiency (PCE) of up to 0.07%, 195 mV open-circuit voltage, and 1.28 mA cm –2 short-circuit photocurrent are achieved. The photovoltaic performance is higher for aluminum doped zinc oxide (AZO) substrates than for fluorine doped tin oxide (FTO) due to the presence of a n-/p-junction that further increases the electron selectivity of the AZO/ZnO/Cu 2 O contacts. Overall, this work demonstrates the first application of PEDOT:PSS as a hole transport layer (HTL) for Cu 2 O and the use of VKP-SPV to measure the photovoltage contributions of the Cu 2 O interfaces. Furthermore, the ability to fabricate Cu 2 O solar cells at near room temperature without the use of vacuum methods or rare elements is an important step towards a scalable Cu 2 O PV technology.

14 SOLAR ENERGY↗
DOE OSTI2022

Self-Aligned Selective Area Front Contacts on Poly -Si/SiO x Passivating Contact c -Si Solar Cells

We report both polarity poly-Si/SiO x passivating contacts in a front/back device configuration may represent the next solar cell architecture after tunnel oxide passivating contacts (TOPCon) cells, but high parasitic absorption in the front poly -Si layer often limits its performance. This work explores a wet etching technique to remove the front poly -Si in the nonmetallized regions using self-aligned metal grids as an etch mask. We systematically examine various dielectric layers (SiN x ,Al 2 O 3 , and stacks thereof) to study the repassivation of the etched n + surface, and find that an SiN x /Al 2 O 3 passivation stack can effectively repassivate the etched surface, which we attribute to field-effect passivation from the positive fixed charge from the SiN x layer, and excellent chemical passivation property from Al 2 O 3 in the form of atomic H. We demonstrate a front/back poly-Si/SiO x passivating contact device, with an open-circuit voltage (V oc ) of 690 mV, short-circuit current density (J sc ) of 39.8 mA/cm 2 , fill factor of 78%, and power conversion efficiency of 21.4%. Furthermore, simulations using SunSolve and Quokka 3 show good agreement with both the optical and electrical properties of the experimental device. The power loss analysis reveals improvements in the optical loss from the back Ti adhesion and front SiN x layers would lead to a 23.5% device. Lastly, a techno-economic model compares the production cost of this improved cell with the current TOPCon cells. Our results highlight that further cost reductions in single-sided doped poly -Si layers are needed to compete with mainstream passivated emitter and rear cell, and TOPCon technologies.

14 SOLAR ENERGY↗
DOE OSTI2020

A New Approach to Indoor Characterization of PV Module Energy Yield Parameters

Temperature and solar irradiance are among the most relevant parameters that affect the energy yield of photovoltaic cells and modules. A rise in the module temperature leads to a significant decrease in the open circuit voltage and a small increase in the short circuit current. Here we use a new tool to determine temperature coefficients as well as to assess power rating of multi c-Si, mono c-Si, CdTe, and CIGS-based PV modules in controlled indoor conditions per IEC 60891 and IEC 61853-1. We use the tool to explore how nonuniformities in module temperature affect the accuracy of the temperature coefficients.

14 SOLAR ENERGY↗
DOE OSTI2022

Statistical Performance Analysis on Approximately 320 Perovskite Single- and Two-Junction Solar Cells and Modules from >30 Global Sources

As perovskite photovoltaics (PV) advance from the laboratory to commercial prototypes, their accurate and reliable performance testing is becoming increasingly important. The well documented dynamic response of perovskite solar cells to an external applied voltage has led to the development of steady-state performance measurement methods; however, these methods have not been widely adopted by the perovskite PV community. A key reason for this is that steady-state measurement methods take tens of minutes to complete, as opposed to conventional "fast" current-voltage (I-V) measurements usually lasting a few seconds. Fast I-Vs arise from a snapshot, almost always not a steady-state condition of the device; however, given their widespread use, the question arises: how do performance parameters of perovskite PV compare when measured with fast I-V and with a steady-state method? We compile results from ca. 320 perovskite PV cells and modules, including single junction, and two-terminal perovskite-perovskite and perovskite-Si tandems, and show that fast I-Vs can provide a useful measure of the open-circuit voltage of the devices, while the short-circuit current and the overall efficiency can be widely misestimated. We discuss implications of these findings on performance testing protocols and propose possible options for fast and accurate testing of perovskite PV.

asymptotic↗
DOE OSTI2021

Study of the Heater-Coil Electrical Insulation for the HL-LHC Low Beta Quadrupoles

In the framework of the HL-LHC project, the present LHC low-β superconducting quadrupoles will be substituted with higher performance Nb 3 Sn magnets (MQXF) with 11.4 T coil peak field. MQXF coils are impregnated with epoxy resin to reduce risk of stress concentration on the brittle conductor. The magnet quench protection is provided by CLIQ and quench heaters to ensure a redundant system. Quench heaters are impregnated with the coils in order to have suitable thermal contact with them, and to prevent the hot spot temperature from exceeding 350K during normal operation in case of a quench. Quench heaters are insulated from the coil by S-2 Glass and polyimide. Here, the test of the first MQXF prototype (4 m long) MQXFAP1 was stopped by a coil-to-ground short circuit triggered by a heater-to-coil short. This issue triggered a root analysis of the causes of this short. Here we prove that the use of a non-conforming cloth in coil impregnation, further weakened by non-conforming high voltage test, has triggered the shorts. Moreover, we present an analysis of the heater-to-coil insulation strength, showing the role of blistering phenomena and how they are triggered by a combination of magnet powering and heater firing.

43 PARTICLE ACCELERATORS↗
NASA NTRS1995

Lightweight, light-trapped, thin GaAs solar cell for spacecraft applications: Progress and results update

Progress is reported with respect to the development of ultra-lightweight, high performance, thin, light trapped GaAs solar cells for advanced space power systems. Conversion efficiencies of over 17.7% have been demonstrated for a 3 micron thick, 1 sq cm silicone bonded solar cell. This results in a specific power of over 1020 W/kg. Device parameters were 1.011 V open circuit voltage, 80% fill factor, and a short-circuit current density of 29.5 mA/sq cm . In addition to silicone bonding, the use of electrostatic bonding to attach the coverglass support to the front surface enables an ultra-thin, all back contact design that survives processing temperatures greater than 750 C. This also results in a 10% reduction of the cell weight for a potential specific power of 1270 W/kg. All back contact, ultra-thin, electrostatically bonded GaAs solar cell prototypes have been completed demonstrating an open circuit voltage of 1 volt for a cell base thickness of 1 micron with a 0.5 micron emitter. This technology will result in a revolutionary improvement in survivability, performance, and manufacturability of lightweight GaAs solar cell products for future Earth-orbiting science and space exploration missions. The thin, electrostatically bonded, all back contact GaAs device technology has multiple uses for specialty high performance solar cells and other optoelectronic devices.

Hannon, M. H.↗
NASA NTRS1975

The 7.5 kW solar array simulator

A high power solar array simulator capable of providing the input power to simultaneously operate two 30 cm diameter ion thruster power processors was designed, fabricated, and tested. The maximum power point is set to between 150 and 7500 watts representing an open circuit voltage from 50 to 300 volts and a short circuit current from 4 to 36 amps. Illuminated solar cells are used as the control element to provide a true solar cell characteristic and permit the option of simulating changes in this characteristic due to variations in solar intensity and/or temperature of the solar array. This is accomplished by changing the illumination and/or temperature of the control cells. The response of the output to a step change in load closely approximates that of an actual solar array.

Robson, R. R.↗
NASA NTRS1975

7.5 kW solar array simulator

A high power solar array simulator capable of providing the input power to simultaneously operate two 30 cm diameter ion thruster power processors was designed, fabricated, and tested. The maximum power point may be set to between 150 and 7500 watts. This represents an open circuit voltage from 50 to 300 volts and a short circuit current from 4 to 36 amps. Illuminated solar cells are used as the control element. The illuminated solar cells provide a true solar cell characteristic and permit the option of simulating changes in this characteristic due to variations in solar intensity and/or temperature of the solar array. This is accomplished by changing the illumination and/or temperature of the control cells. The response of the output to a step change in load closely approximates that of an actual solar array.

Robson, R. R.↗
NASA NTRS1983

GaAs solar cells for concentrator systems in space

Cells for operation in space up to more than 100 suns were made, and an AMO efficiency of 21% at 100 suns with these cells was obtained. The increased efficiency resulted not only from the higher open circuit voltage associated with the higher light intensity (higher short circuit current); it also benefitted from the increase in fill factor caused by the lower relative contribution of the generation recombination current to the forward bias current when the cell's operating current density is increased. The experimental cells exhibited an AMO efficiency close to 16% at 200 C. The prospect of exploiting this capability for the continuous annealing of radiation damage or for high temperature missions (e.g., near Sun missions) remains therefore open. Space systems with concentration ratios on the order of 100 suns are presently under development. The tradeoff between increased concentration ratio and increased loss due to the cell's series resistance remains attractive even for space applications at a solar concentrator ratio of 100 suns. In the design of contact configuration with low enough series resistance for such solar concentration ratios, the shallow junction depth needed for good radiation hardness and the thin AlGaAs layer thickness needed to avoid excessive optical absorption losses have to be retained.

Loo, R. Y.↗
NASA NTRS1989

InP shallow-homojunction solar cells

Indium phosphide solar cells with very thin n-type emitters have been made by both ion implantation and metalorganic chemical vapor deposition. Air mass zero efficiencies as high as 18.8 percent (NASA measurement) have been achieved. Although calculations show that, as is the case with GaAs, a heterostructure is expected to be required for the highest efficiencies attainable, the material properties of InP give the shallow-homojunction structure a greater potential than in the case of GaAs. The best cells, which were those made by ion implantation, show open-circuit voltage (V sub oc) of 873 mV, short-circuit current of 357 A/sq m (35.7 mA/sq cm), and fill factor of 0.829. Improvements are anticipated in all three of these parameters. Internal quantum efficiency peaks at over 90 percent in the red end of the spectrum, but drops to 54 percent in the blue end. Other cells have achieved 74 percent in the blue end. Detailed modeling of the data indicates that a high front surface recombination velocity is responsible for the low blue response, that the carrier lifetime is high enough to allow good carrier collection from both the base and the emitter, and that the voltage is base-limited.

Keavney, Christopher↗
NASA NTRS1994

Two-Stage Series-Resonant Inverter

Two-stage inverter includes variable-frequency, voltage-regulating first stage and fixed-frequency second stage. Lightweight circuit provides regulated power and is invulnerable to output short circuits. Does not require large capacitor across ac bus, like parallel resonant designs. Particularly suitable for use in ac-power-distribution system of aircraft.

Stuart, Thomas A.↗