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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

The Effect of Dopant Concentration and Annealing Treatments on N-Type Iodine Doped CdTe

We report properties of highly conducting n-type cadmium telluride single crystals doped with iodine (CdTe:I). These crystals were grown with dopant concentrations in the range of 10^17 cm-3 to 10^19 cm-3 by Modified Vertical Bridgman (MVB) melt growth. Post-growth dopant activation, including Cd annealing, Te annealing, and rapid thermal annealing (RTA), was applied to improve free carrier density. The structural, optical, and electrical properties were analyzed by Glow Discharge Mass Spectroscopy (GDMS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Photoluminescence Spectroscopy (PL), optical absorption, Hall measurements, Capacitance-Voltage (CV) measurements, and time-resolved photoluminescence (TRPL). The results indicate that Cd annealing is the most effective activation method to get 100% donor activation (n is approximately 2 x 10^18 cm-3), which is close to the room temperature solubility limit of iodine. This leads to the lowest resistivity and the highest mobility. Moreover, this data suggests a potential role of Cd vacancy-related defects on electrical self-compensation.

annealing↗
DOE OSTI2024

First-Principles Study on the Role of Cu and Cl-Based Dopants in NiO

Utilization of wide band gap oxide-based materials in thin-film solar energy technologies has increased in recent years. Among the numerous candidate oxide materials, NiO has shown many desirable optoelectronic properties that are applicable to thin-film PV technologies such as cadmium telluride PV. However, one critical factor requiring further investigation is the p-type doping behavior of NiO, specifically when the cadmium telluride solar cell undergoes conventional processes such as copper doping and chlorine-based activation treatment. The previous literature has shown a large degree of variability in hole concentrations in NiO when copper is used as the primary dopant. This study uses first-principles computational modeling based on density functional theory coupled with defect equilibria calculations to quantitatively explore the role of copper and chlorine-based extrinsic dopants in the p-type doping activity of NiO. The study reveals the importance of extrinsic dopants and their binding interactions with nickel vacancies to effectively p-dope NiO. It is suggested that both the formation of V Ni + Cu Ni and V Ni + Cl O defect pairs under a supersaturated state of NiO are potential mechanisms for increasing hole densities. On the other hand, the production of 2Cu Ni severely limits the effectiveness of p-doping in NiO, even in the presence of the aforementioned defect pairs. Furthermore, the study provides a guideline for experimentalists interested in using copper or chlorine species to understand how to controllably p-dope NiO during thin-film synthesis.

chlorine↗
DOE OSTI2025

ZnGa 2 Te 4 thin-film absorbers for photoelectrochemical CO 2 reduction

Photoelectrochemical (PEC) carbon dioxide reduction reaction (CO 2 RR) has been considered as a promising route to convert and store solar energy into chemical fuels. It is crucial to find suitable photoelectrode materials that are photo-catalytically active and exhibit excellent photochemical stability. One of the promising contenders is ZnTe with the ∼2.26 eV band gap and prolonged stability under CO 2 RR PEC conditions. Herein, a new telluride based thin-film ZnGa 2 Te 4 photocathode with lower band gap and stronger visible light absorption compared to ZnTe is synthesized and characterized using a combinatorial sputtering technique. A two-step annealing method with excess Te supply is implemented to synthesize nearly stoichiometric ZnGa 2 Te 4 absorber material with a zincblende-derived tetragonal crystal structure confirmed by synchrotron X-ray and electron diffraction. Theoretical calculations show that ZnGa 2 Te 4 has suitable direct bandgap (∼1.86 eV) and high absorption coefficient ∼10 5 cm −1 , in agreement with experimentally prepared films. Transient absorption spectroscopy reveals the biexponential decay dynamics, with time constants, τ 1 ∼ 0.04, and τ 2 ∼ 0.65 μs in microsecond time scales and provides the optical transition pathways for this semiconductor thin film. PEC measurements show that the ZnGa 2 Te 4 photocurrent densities are comparable to the widely investigated ZnTe photocathodes or even surpass it under simulated sunlight condition. ZnGa 2 Te 4 samples demonstrate promising photoelectrochemical stability, maintaining consistent performance under illumination. The inclusion of diaryliodonium additive substantially increases its CO 2 RR selectivity to ∼60%. These findings open a new avenue for the synthesis of telluride-based thin-film photocathodes for further exploration and will motivate future research to integrate this potential photocathode material into PEC devices.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Gepta-EX: a multi-channel germanium detector for X-ray absorption fine structure

Fluorescence-mode X-ray absorption spectroscopy (XAS) at high photon energies requires detectors with high stopping power and excellent energy resolution to measure weak element-specific signals. Traditional silicon-based detectors suffer from poor efficiency above ∼20 keV, while most high-Z materials such as cadmium telluride, cadmium zinc telluride, and gallium arsenide have focused predominantly on imaging applications with limited spectroscopic resolution. In contrast, germanium combines excellent stopping power with superior intrinsic energy resolution due to its low Fano factor and favorable charge transport properties, making it ideal for high-resolution spectroscopy in the 15 keV to 100 keV range. To address these requirements, we report on the development, fabrication, and performance evaluation of Gepta-EX, a compact multi-channel high-purity germanium (HPGe) detector system for fluorescence-mode XAS. The Gepta-EX system features a monolithic seven-channel HPGe pixel array integrated with low-noise CUBE charge-sensitive preamplifiers, housed within a thermally isolated compact cryostat operating near 90 K. The detector achieves energy resolutions of 218 eV at 5.9 keV (from a 55 Fe source) and 373 eV at 59.5 keV (from a 241 Am source), with uniform performance across all channels. By avoiding the escape peak interference commonly associated with silicon detectors and providing stable, high-resolution performance, Gepta-EX represents a powerful tool for high-energy X-ray spectroscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Mapping Current Collection in Cross Section: The Case of Copper-Doped CdTe Solar Cells

For decades, copper has been used to improve the performance of cadmium telluride thin film solar cells. However, it has also been shown to be the main cause of metastability in CdTe. Recently a low activation energy has been reported for the thermal diffusion of Cu in CdTe explaining the ease of motion that it has under moderate temperatures. The community consensus is that copper segregates to the absorber grain boundaries, where it's either beneficial or detrimental to device performance depending on its concentration. Using nanoscale X-ray micrsocopy and a two-dimensional drift-diffusion model we present a preliminary correlation between local copper distribution and electrical performance of a single-junction CdTe/CdS solar cell.

CdTe↗
DOE OSTI2024

Low-cost Manufacturing of Semitransparent CdTe PV for Building Integration

Solar has been demonstrated to be a robust renewable energy source, constituting a significant portion of the United States’ renewable energy portfolio. Despite its growth across residential, commercial, and utility sectors over the past decades, it remains a small fraction of the overall energy infrastructure. Challenges persist in fully harnessing solar power to meet the nation's escalating energy demands. Among these challenges lies the hurdle of efficiently distributing large quantities of solar-generated electricity to densely populated regions with the highest energy needs and costs. Traditional utility-scale arrays demand extensive land, a luxury often unavailable in metropolitan areas. Consequently, installations must be situated at a distance, necessitating additional infrastructure for electricity transmission to service areas. While metropolitan landscapes lack sprawling open spaces suitable for conventional utility-scale solar deployment, they offer a different resource: windows. Semitransparent photovoltaic window technology has the potential to not only bolster the grid's energy capacity, but to also provide HVAC and economic advantages to building owners. However, commercial availability of building-integrated photovoltaic windows remains limited. Silicon based photovoltaics currently dominate the solar market but adapting them for use in windows poses a variety of engineering and economic challenges such as relatively low power density, high costs associated with custom manufacturing, and aesthetic considerations. Addressing these challenges, this project explored the use of laser ablation patterning to manufacture cost-effective, high-efficiency, semitransparent Cadmium Telluride photovoltaic modules. Results showcased the potential of this methodology in developing photovoltaic windows and other innovative semitransparent PV applications. The ablation manufacturing technique demonstrated great versatility in achieving different patterns and levels of visible light transmission, and the power loss due to ablation was nearly directly proportional to the amount of material removed. Furthermore, the manufacturing process for Cadmium Telluride modules already has established advantages in material and energy efficiency, and the conversion of a standard submodule to semitransparent essentially requires a single additional process step, ensuring scalability. It is important to note that during this work, Toledo Solar experienced substantial organizational upheaval stemming from a lawsuit with First Solar. An external investigation led the board of directors to remove and replace the previous management team, and several other members of the staff elected to depart as well, including the then acting Principle Investigator on this project. The remaining Toledo Solar team attempted to recover from the disruption and deliver on the remaining tasks, but upon its own review, the Department of Energy ruled the project in default and terminated the contract in December 2023.

14 SOLAR ENERGY↗
DOE OSTI2025

Effect of Surface Passivation of CZTS Semiconductor Detector on Leakage Current

Cadmium Zinc Telluride Selenide (CdZnTeSe or CZTS)has shown high crystal quality for room-temperature gamma ray and X-ray detection applications compared to Cadmium Zinc Telluride (CdZnTe or CZT) [1,2]. Current applications of CZT include medical imaging, homeland security, and X-ray and gamma ray astronomy [3]. CZST has similar potential applications

Kangethe, Anthony [Morgan State Univ., Baltimore, ↗
DOE OSTI2023

Decoding the Atomic Structure of Ga 2 Te 5 Pulsed Laser Deposition Films for Memory Applications Using Diffraction and First-Principles Simulations

Neuromorphic computing, reconfigurable optical metamaterials that are operational over a wide spectral range, holographic and nonvolatile displays of extremely high resolution, integrated smart photonics, and many other applications need next-generation phase-change materials (PCMs) with better energy efficiency and wider temperature and spectral ranges to increase reliability compared to current flagship PCMs, such as Ge 2 Sb 2 Te 5 or doped Sb 2 Te. Gallium tellurides are favorable compounds to achieve the necessary requirements because of their higher melting and crystallization temperatures, combined with low switching power and fast switching rate. Ga 2 Te 3 and non-stoichiometric alloys appear to be atypical PCMs; they are characterized by regular tetrahedral structures and the absence of metavalent bonding. The sp 3 gallium hybridization in cubic and amorphous Ga 2 Te 3 is also different from conventional p-bonding in flagship PCMs, raising questions about its phase-change mechanism. Furthermore, gallium tellurides exhibit a number of unexpected and highly unusual phenomena, such as nanotectonic compression and viscosity anomalies just above their melting points. Using high-energy X-ray diffraction, supported by first-principles simulations, we will elucidate the atomic structure of amorphous Ga 2 Te 5 PLD films, compare it with the crystal structure of tetragonal gallium pentatelluride, and investigate the electrical, optical, and thermal properties of these two materials to assess their potential for memory applications, among others.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Advances in CdZnTeSe for Radiation Detector Applications

Detection of X- and gamma-rays is essential to a wide range of applications from medical imaging to high energy physics, astronomy, and homeland security. Cadmium zinc telluride (CZT) is the most widely used material for room-temperature detector applications and has been fulfilling the requirements for growing detection demands over the last three decades. However, CZT still suffers from the presence of a high density of performance-limiting defects, such as sub-grain boundary networks and Te inclusions. Cadmium zinc telluride selenide (CZTS) is an emerging material with compelling properties that mitigate some of the long-standing issues seen in CZT. This new quaternary is free from sub-grain boundary networks and possesses very few Te inclusions. In addition, the material offers a high degree of compositional homogeneity. The advancement of CZTS has accelerated through investigations of the material properties and virtual Frisch-grid (VFG) detector performance. The excellent material quality with highly reduced performance-limiting defects elevates the importance of CZTS as a potential replacement to CZT at a substantially lower cost.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1976

Electrochemical deposition of silver crystals aboard Skylab 4

Silver crystals were grown aboard Skylab 4 by an electro-chemical reaction and subsequently returned to earth for comparison with crystals grown at 1- and 5-g. Both the Skylab and earth-grown crystals show a variety of structures. Certain tendencies in structure dependency on gravity level, however, can be discerned. In addition, downward growing dendrite streamers; upward growing chunky crystal streamers; growth along an air/liquid interface; and ribbon, film, and fiber crystal habits were observed in experiments conducted on the ground with solutions of varying concentrations. It was also observed that the crystal structures of space and ground electro-deposited silver crystals were very similar to the structures of germanium selenide and germanium telluride crystals grown in space and on the ground by a vapor transport technique. Consideration of the data leads to the conclusions that: (1) the rate of electrochemical displacement of silver ions from a 5 percent aqueous solution by copper is predominantly diffussion controlled in space and kinetically controlled in 1- and higher-g because of augmentation of mass transport by convection; (2) downward and upward crystal streamers are the result of gravity-driven convection, the flow patterns of which can be delineated. Lateral growths along an air/liquid interface are the result of surface-tension-driven convection, the pattern of which also can be delineated; (3) electrolysis in space or low-g environments can produce either dendritic crystals with more perfect microcrystalline structures or massive, single crystals with fewer defects than those grown on ground or at higher g-levels. Ribbons or films of space-grown silicon crystals would find a ready market for electronic substrate and photocell applications. Space-grown dendritic, metal crystals present the possibility of unique catalysts. Large perfect crystals of various materials are desired for a number of electronic and optical applications; and (4) vapor transport growth of germanium selenide and germanium telluride is affected by convection mechanisms similar to the mechanisms hypothesized for the electrochemical deposition of silver crystals. Evidence and considerations leading to the preceding summaries and conclusions are presented. The implications of the findings and conclusions for technological applications are discussed, and recommendations for further experiments are presented.

Grodzka, P. G.↗
NASA NTRS1976

A CCD scanned (Hg, Cd)Te array for earth viewing applications

A 9 channel demonstration of 10 micrometer photoconductive mercury cadmium telluride detector array, bipolar preamplifiers, and a Si CCD multiplexer, integrated into a focal plane assembly and operating at 105 K and at 17 Hz is reported. The result of a direct coupling experiment between a 5-micrometer photovoltaic mercury cadmium telluride photodiode and a CCD is revealed. No appreciable degradation in the signal-to-noise ratio was experienced.

Iwasa, S.↗
NASA NTRS1978

Design concepts of solar thermoelectric generators in space applications

Several thermoelectric technologies have been examined as to their suitability for use in a solar thermoelectric generator (STG) as a nonpropulsive power source for space applications. The results show that of all the presently available thermoelectric technologies, i.e., lead telluride, bismuth telluride, selenide, and silicon-germanium alloys, the latter type provides the optimum STG. Detailed results are presented on the performance and configurational characteristics of various silicon-germanium alloy STGs, including the performance of such STGs as a function of time in a Mercury orbit and the orbit of Mercury around the sun. It is shown that an STG design based on the use of silicon germanium alloy thermoelectric material, using multiple high voltage thermopiles with individual solar concentrators, presents the optimum combination of technology and configuration for minimizing power source mass. Additional concepts studied and discussed are the flat plate individual thermopile type and single concentrator compact thermopile type. The STG possesses an attractive potential for this application and represents a useful addition to the family of power sources for consideration in various space applications.

Raag, V.↗
NASA NTRS1979

Solar thermoelectric power generation for Mercury orbiter missions

Mercury orbiter mission study results have shown that conventional silicon solar cell array technology is not adequate to produce power because of expected temperatures which range from -90 C to +285 C in about 50 minutes for 16 sun eclipses/day. The solar thermoelectric generator (STG), which requires relatively high temperatures, is being developed as a replacement power source. Several thermoelectric technologies (i.e., lead telluride alloys, bismuth telluride, selenide, and silicon-germanium alloys have been examined for their suitability. Solar concentrator configurations (i.e., flat plate, Fresnel lens, mini-cone, and Cassegrain types) were also studied as candidates for increasing incident radiation during Mercury orbital operations. Detailed results are presented, and show that an STG design based on the use of silicon-germanium alloy thermoelectric material and using high-voltage thermopiles with individual miniconical concentrators presents the optimum combination of technology and configuration for minimizing power source mass.

Swerdling, M.↗
NASA NTRS1982

Space processing of electronic materials

The bulk growth of solid solution alloys of mercury telluride and cadmium telluride is discussed. These alloys are usually described by the formula Hg1-xCdxTe, and are useful for the construction of infrared detectors. The electronic energy band gap can be controlled between zero and 1.6 electron volts by adjusting the composition x. The most useful materials are at x approximately 20%, suitable for detection wavelengths of about 10 micrometers. The problems of growing large crystals are rooted in the wide phase diagram of the HgTe-CdTe pseudobinary system which leads to exaggerate segregation in freezing, constitutional supercooling, and other difficulties, and in the high vapor pressure of mercury at the growth temperatures, which leads to loss of stoichiometry and to the necessity of working in strong, pressure resistant sealed containers.

Holland, L. R.↗
NASA NTRS1985

Thermoelectric properties of rare earth chalcogenides

The rare earth chalcogenides are important thermoelectric materials due to their high melting points, self-doping capabilities, and low thermal conductivities. Lanthanum sulfides and lanthanum tellurides have been synthesized in quartz ampules, hot-pressed into samples, and measured. The n-type Seebeck coefficients, electrical resistivities, and power factors generally all increased as the temperature increased from 200 to 1000 C. The figure-of-merit for nonstoichiometric lanthanum telluride was 0.001/deg C at 1000 C, considerably higher than for silicon-germanium. Thermoelectric measurements were made for LaTe(2) and YbS(1.4), and p-type behavior was observed for these compounds from 300 to 1100 C.

Danielson, L. R.↗
NASA NTRS1988

Electrochemical Growth Of Crystals In Gels

Nucleation and growth rates readily controlled. Technique developed to grow crystals by controlling rate of transfer of one component into crystallization volume. Method involves electrochemically controlled generation of one of precipitation species, coupled with diffusion barrier. New procedure, developed in connection with formation of lead tin telluride by reaction in gels of metal ions with telluride ions.

Barber, Patrick G.↗
NASA NTRS1991

Radiation resistance of thin-film solar cells for space photovoltaic power

Copper indium diselenide, cadmium telluride, and amorphous silicon alloy solar cells have achieved noteworthy performance and are currently being studied for space power applications. Cadmium sulfide cells had been the subject of much effort but are no longer considered for space applications. A review is presented of what is known about the radiation degradation of thin film solar cells in space. Experimental cadmium telluride and amorphous silicon alloy cells are reviewed. Damage mechanisms and radiation induced defect generation and passivation in the amorphous silicon alloy cell are discussed in detail due to the greater amount of experimental data available.

Woodyard, James R.↗
NASA NTRS1992

Electron mobility in n-type Hg(1-x)Cd(x)Te and Hg(1-x)Zn(x)Te alloys

Calculations of electron mobility in n-type mercury cadmium telluride (MCT), a candidate material for IR detectors, and n-type mercury zinc telluride (MZT) are compared. It is found that electron mobilities in MCT and MZT are nearly the same for equivalent energy gaps. The results are also found to compare will with experimental data. Directions of future research are briefly discussed.

Patterson, J. D.↗