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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Ultra-thin passivation layers in Cu(In,Ga)Se 2 thin-film solar cells: full-area passivated front contacts and their impact on bulk doping

In the search for highly transparent and non-toxic alternative front layers replacing state-of-the-art CdS in Cu(In,Ga)Se 2 thin-film solar cells, alternatives rarely exceed reference devices in terms of efficiency. Full-area ultra-thin aluminium oxide tunnelling layers do not require any contact patterning and thus overcome the main drawback of insulating passivation layers. Even a few monolayers of aluminium oxide can be deposited in a controlled manner by atomic layer deposition, they show excellent interface passivation properties, low absorption, and suitable current transport characteristics on test devices. Depositing a ZnO-based transparent front contact, however, results in extremely poor solar cell performance. The issue is not necessarily a low quality of the alternative front layer, but rather the intricate relation between front layer processing and electronic bulk properties in the absorber layer. We identify three challenges critical for the development of novel front passivation approaches:(i) both Cd and Zn impurities beneficially reduce the high native net dopant concentration in the space charge region, (ii) sputter deposition of ZnO damages the passivation layer resulting in increased interface recombination, (iii) thermal treatments of devices with ZnO layer result in substantial Zn diffusion, which can penetrate the full absorber thickness already at moderate temperatures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

In silico prediction of MOFs with high deliverable capacity or internal surface area

Metal–organic frameworks (MOFs) offer unprecedented atom-scale design and structural tunability, largely due to the vast number of possible organic linkers which can be utilized in their assembly. Exploration of this space of linkers allows identification of ranges of achievable material properties as well as discovery of optimal materials for a given application. Experimental exploration of the linker space has to date been quite limited due to the cost and complexity of synthesis, while high-throughput computational studies have mainly explored MOF materials based on known or readily available linkers. Here an evolutionary algorithm for de novo design of organic linkers for metal–organic frameworks is used to predict MOFs with either high methane deliverable capacity or methane accessible surface area. Known chemical reactions are applied in silico to a population of linkers to discover these MOFs. Through this design strategy, MOF candidates are found in the ten symmetric networks acs, cds, dia, hxg, lvt, nbo, pcu, rhr, sod, and tbo. Furthermore, the correlation between deliverable capacities and surface area is network dependent.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Morphology inherence from hollow MOFs to hollow carbon polyhedrons in preparing carbon-based electrocatalysts

Hollow carbon nanostructures are emerging as advanced electrocatalysts for the oxygen reduction reaction (ORR) due to the effective usage of active sites and the reduced dependence on expensive noble metals. Conventional preparation of these hollow structures is achieved through templates (e.g. SiO 2 , CdS, and Ni 3 C), which serve to retain the void interiors during carbonization, leading to an essential template-removal procedure using hazardous chemical etchants. Herein, we demonstrate the direct carbonization of unique hollow zeolitic imidazolate frameworks (ZIFs) for the synthesis of hollow carbon polyhedrons (HCPs) with well-defined morphologies. The hollow ZIF particles behave bi-functionally as a carbon source and a morphology directing agent. This method evidences the strong morphology inherence from the hollow ZIFs during the carbonization, advancing the significant simplicity and environmental friendliness of this synthesis strategy. The as-prepared HCPs show a uniform polyhedral morphology and large void interiors, which enable their superior ORR activity. Iron can be doped into the HCPs (Fe/HCPs), providing the Fe/HCPs with enhanced ORR properties ( E 1/2 = 0.850 V) in comparison with those of HCPs. As a result, we highlight the efficient structural engineering to transform ZIFs into advanced carbon nanostructures accomplishing morphological control and high electrocatalytic activity.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Synthesis, properties, and formation mechanism of Mn-doped Zn 2 SiO 4 nanowires and associated heterostructures

In this study, we have put forth a facile hydrothermal approach to synthesize an array of one-dimensional (1D) Mn-doped Zn 2 SiO 4 nanostructures. Specifically, we have probed and correlated the effects of controllable reaction parameters such as the pH and Mn dopant concentrations with the resulting crystal structures and morphologies of the products obtained. Based upon our results, we find that careful tuning of the pH versus the Mn dopant level gives rise to opposite trends with respect to the overall size of the resulting one-dimensional nanostructures. Significantly, we have highlighted the role of the Mn dopant ion concentration as a potentially generalizable reaction parameter in solution-based synthesis for controlling morphology and hence, the observed optical behavior. Indeed, such a strategy can be potentially generalized to systems such as but not limited to Mn-doped ZnS, CdS, and CdSe quantum dots (QD), which, to the best of our knowledge, denote promising candidates for a variety of optoelectronic applications. Specifically, we have carefully optimized the synthesis conditions in order to generate a series of chemically well-defined Mn-doped Zn 2 SiO 4 not only possessing Mn concentrations ranging from 3% to 8% but also characterized by highly crystalline, monodisperse wire-like motifs measuring ~30 nm in diameter and ~700 nm in length. Optically, the photoluminescence signals associated with the 1D series yielded a volcano-shaped relationship between PL intensities and the Mn dopant level. In additional experiments, we have immobilized CdSe quantum dots (QDs) onto the external surfaces of our as-synthesized Mn-doped Zn 2 SiO 4 nanowires, in order to form novel composite heterostructures. The optical properties of the CdSe QD–Mn:Zn 2 SiO 4 heterostructures have been subsequently examined. Our results have demonstrated the likely co-existence of both energy transfer and charge transfer phenomena between the two constituent components of our as-prepared composites. Specifically, when both components are photoexcited, both energy transfer and charge transfer were found to plausibly occur, albeit in opposite directions. When the CdSe QDs are excited alone for example, charge transfer probably takes place from the CdSe QDs to the dopant Mn 2+ ions. We believe that our as-processed heterostructures are therefore promising as a tunable light-harvesting motif. Essentially, these materials have broadened the effective light absorption range for optical ‘accessibility’, not only through their incorporation of dopant-tunable Zn 2 SiO 4 possessing complementary absorption properties to those of the QDs but also through their integration of CdSe QDs with size-tailorable optical behavior.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

In situ Al 2 O 3 incorporation enhances the efficiency of CuIn(S,Se) 2 solar cells prepared from molecular-ink solutions

Here, we report an efficiency enhancement of solution-processed CuIn(S,Se) 2 (CISSe) thin film solar cells via in situ incorporation of Al 2 O 3 . These films were produced using inks containing CuCl, InCl 3 , AlNO 3 (Al/Al + In: 0.1) and thiourea dissolved in methanol. After spin coating of these solutions in air, samples were subjected to a selenization process. Auger electron spectroscopy depth-profiling analysis showed that Al is evenly distributed throughout the bulk of the film. Transmission electron microscopy revealed that AlNO 3 precursor reacted with oxygen to form nanosized amorphous Al 2 O 3 grains located within the bulk and grain boundaries of CISSe, as well as at both the top and bottom interfaces. Power conversion efficiency (PCE) as high as 11.6% (JS C : 35.8 mA cm –2 , V OC : 518 mV, FF: 62.2%, no anti-reflection coating) was achieved with Al–CISSe solar cell devices integrated with CdS (chemical bath deposition, thickness: 80 nm) and ZnO/ITO bilayers (sputtered, thickness: 300 nm). The average PCE (10.1%, $\langle$J SC $\rangle$: 34.5 mA cm –2 , $\langle$V OC $\rangle$: 491 mV, $\langle$FF$\rangle$: 59.8%) was nearly 4% (absolute) higher than that measured on CISSe baseline cells fabricated from solutions without Al ($\langle$PCE$\rangle$ = 6.4%, $\langle$J SC $\rangle$: 32.8 mA cm –2 , $\langle$V OC $\rangle$: 410 mV, $\langle$FF$\rangle$: 47.3%). This in situ Al 2 O 3 incorporation is speculated to play a role in the enhancement of the VOC and FF of the devices through passivation of defects in CISSe reducing interface and bulk recombination, as evidenced by a reduced defect density and an increased activation energy of the dominant recombination mechanism from capacitance and temperature-dependent VOC measurements, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Optoelectronic property comparison for isostructural Cu 2 BaGeSe 4 and Cu 2 BaSnS 4 solar absorbers

To target mitigation of anti-site defect formation in Cu 2 ZnSnS 4–x Se x , a new class of chalcogenides, for which Ba or Sr (group 2) replace Zn (group 12), has recently been introduced for prospective solar absorber application. Cu 2 BaGeSe 4 (CBGSe) and Cu 2 BaSnS 4 (CBTS) are two such compounds, which share a common trigonal crystal structure (P3 1 space group) and similar quasi-direct band gap (~2 eV). While CBTS-based films have already been studied, there are no reports yet on films and solar cells based on related CBGSe. To identify key differences and similarities in the electronic properties between these two materials, electronic characteristics (e.g., carrier concentration, mobility, electron affinity, defect levels, recombination, and charge carrier kinetics) of vacuum-deposited CBGSe and CBTS films are compared using a variety of characterization methods. Hall effect measurements reveal that CBGSe films have relatively higher hole carrier concentration and lower mobility (3 × 10 15 cm –3 , 0.6 cm 2 V –1 s –1 ) compared to CBTS (5 × 10 12 cm –3 , 3.5 cm 2 V –1 s –1 ). Photoelectron spectroscopy yields low electron affinity values for both CBGSe (3.7 eV) and CBTS (3.3 eV), pointing to the necessity of pursuing low electron affinity buffer materials for both types of absorbers. At low temperatures, CBGSe films show free-exciton photoluminescence, as well as pronounced deep-level emission at ~1.4 eV, while CBTS films exhibit a strong bound-exciton signal with noticeably less intense deep-level emission than for CBGSe. Charge carrier kinetics, transport, and recombination properties of both types of films are also analyzed using optical-pump terahertz-probe spectroscopy and time-resolved microwave conductivity. The first CBGSe prototype solar cells (using chemical bath deposited CdS as a buffer layer) show a maximum of 1.5% efficiency with ~0.62 V open-circuit voltage. Furthermore, the measured properties point to possible limiting factors for CBGSe and related films for PV and optoelectronics and provide insights on possible approaches for improvement within this multinary chalcogenide family.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Continuous-flow reactor with superior production rate and stability for CO 2 reduction using semiconductor photocatalysts

Semiconductor photocatalyst approaches for solar CO 2 reduction are attractive due to their simplicity but have lagged in efficiency compared to less-integrated photoelectrochemical (PEC) approaches and to electrolysis reactors. We identify poor mass transport and catalyst deactivation as key constraints. To address them, we have developed a continuous-flow photocatalytic reactor system allowing us to control the triple-phase interface on the photocatalyst surface using the liquid and reactant gas flow rates. With the goal of selectively producing CO, the reactor is optimized by controlling the pressure and flow rates of the reactant gas and electrolyte in contact with both sides with the intermediately placed catalyst. In comparison to batch reactors with an immobile photocatalyst bed and gas phase CO 2 or CO 2 purged water, 10–24 times higher production rates are achieved for photocatalysts such as TiO 2 , ZnO, C 3 N 4 , and CdS by simply changing to the designed flow-type photoreactor without any catalyst modification. In addition, CO selectivity (93.2%) and long-term stability (>780 min) using the designed reactor are significantly enhanced compared to using the batch reactors (71.7%, <180 min for reduced 50% activity). Here, we propose that the enhanced mass transport on the photocatalyst surface accelerates the desorption of the initial photolysis product, CO, and prevents the poisoning effect from deactivating photocatalyst activity. This study has the potential to facilitate the utilization of semiconductor-based photocatalytic reactions for achieving superior performance wih gaseous reactants.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Power conversion in SnS photocathodes made by electrochemical growth is limited by recombination at (002) buried facets

Herzenbergite α-SnS is a promising p-type semiconductor for photovoltaic and solar fuel applications, but current devices are plagued by substantial photovoltage losses. Here we use vibrating Kelvin probe surface photovoltage for the first time to study the recombination losses in microcrystalline SnS photoelectrodes. α-SnS films of varied crystal orientation, size, and shape are obtained by electrochemical growth from aqueous tin( II ) chloride and sodium thiosulfate solutions near room temperature. After application of a CdS passivation layer, the films function as photocathodes for the methylviologen reduction reaction. Photoelectrochemical and surface photovoltage measurements reveal that the performance of these devices is sensitively controlled by mainly the SnS crystal orientation and to a lesser extent by the grain size. For example, the highest charge recombination rates of 8.97 × 10 14 s −1 cm −2 and lowest photocurrent (0.73 mA cm −2 ) and lowest photovoltage (0.12 V) occur for SnS films containing 500 nm crystals with irregular shapes and SnS lattices tilted away from the (001) orientation. On the other hand, the best performance (1.62 mA cm −2 , 0.16 V, 3.32 × 10 12 s −1 cm −2 ) is seen for 1100 nm fully (001) oriented SnS nanoplates. Furthermore, these findings agree with improved charge carrier mobility in the 001 direction and they also show that charge recombination in SnS films occurs mainly at dangling Sn–S bonds at buried (002) facets. Such buried interfaces need to be suppressed for optimized solar energy conversion with SnS.

Najaf, Zainab [University of California, Davis, CA↗
DOE OSTI2026

Strong Effect of Nonpolar Solvent Molecular Structure on CdSe Nanoplatelet Stacking

We report a drastic difference in stacking behavior of oleic acid-stabilized 4-monolayer (4 ML) CdSe nanoplatelets (NPLs) in toluene and methylcyclohexane (MCH), two nonpolar solvents that differ in the conformational flexibility of their molecules. Using liquid cell transmission electron microscopy (TEM) and small angle scattering (SAXS) techniques, we show that NPLs form microns-long ribbons consisting of 4 ML CdSe NPLs in toluene, the solvent widely used to form stable colloidal solutions of a broad range of quasi-spherical nanoparticles. In contrast, 4 ML CdSe NPLs are well dispersed in MCH. The difference in stacking behavior of NPLs in toluene and MCH suggests that the conformational flexibility of the solvent molecules, such as the ability to adopt multiple chair conformations, modulates nanoplatelet interactions. Molecular dynamics (MD) simulations reveal that solvent molecules subtly alter the structure of the organic ligand shell. These solvent-dependent changes propagate to the inorganic core, modulating the degree of CdSe nanoplatelet (NPL) twisting and, consequently, the properties of the nanoparticles. We show that toluene better solvates oleate ligands while MCH induces a bimodal oleate span distribution, which can lead to increased solubility of CdSe NPLs. In addition, the solvent can also influence the inorganic core, which, in turn, can modify the nanoparticle properties. We demonstrate that destabilization of toluene solution containing ribbons of 4 ML CdSe NPLs without CdS shells results in the formation of NPL assemblies with amplified spontaneous emission (ASE) with a low threshold of 14 µJ cm−2 that is comparable with that of CdSe/CdS core/shell NPLs. Our results emphasize that the solvent plays a major role in mediating interactions between NPLs and hence their processability for fabrication of functional structures.

CdSe↗
DOE OSTI2019

STEM characterization of solar cells

Photovoltaic (PV) devices consisting of a thin-film CdTe absorber layer on glass support have long been considered one of the leading technologies for reaching the Department of Energy’s 2030 cost target of less than 0.03/kWh. Here, the currently used device architectures include a thin transparent conductive oxide (TCO) on top of the glass superstrate following by very thin (<100 nm) polycrystalline emitter layer, typically CdS or more recently MgZnO (MZO). The CdTe absorber layer is usually up to 4 µm thick and polycrystalline, followed by the back contact (Figure 1). Typical CdTe thin-film layers are formed from rapid deposition techniques, such as close-spaced sublimation (CSS) or high-rate vapor-transport deposition (HRVDT). Both processes result in a polycrystalline CdTe photo-absorbing film, and such devices can be manufactured cheaply and efficiently at large scale. Record cell efficiencies as high as 22.1% have been demonstrated. However, such cell performances are still far from the theoretical limits (~30% for CdTe), and improvements have mostly been due to better light collection, rather than improvements in absorber conversion efficiency. The remaining obstacles to further improving these devices toward their theoretical limits concern improvements in the fill factor (FF) and, more importantly, open-circuit voltage (V oc ), which is still far from its limit. In fact, it is widely accepted that V oc is the limiting factor since it reaches only about 60% of the CdTe bandgap. This is in contrast to GaAs solar cells, which have reached a V oc of 80% of the bandgap. The reasons for this discrepancy have been identified as the low p -type doping concentrations of CdTe due to the formation of compensating defect states, a poor p-n junction, and the need for better backside ohmic contacts. High interfacial defect density at grain boundaries (GBs) and intragrain dislocations is also one of the main concerns because they contribute to the dark current. This is supported by the study of single-crystal-based CdTe solar cells that were able to reach Voc in excess of 1 V.

14 SOLAR ENERGY↗
DOE OSTI2020

Event Horizon Telescope imaging of the archetypal blazar 3C 279 at an extreme 20 microarcsecond resolution

3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variability across the entire electromagnetic spectrum. We use an ultra-high angular resolution technique – global Very Long Baseline Interferometry (VLBI) at 1.3 mm (230 GHz) – to resolve the innermost jet of 3C 279 in order to study its fine-scale morphology close to the jet base where highly variable γ-ray emission is thought to originate, according to various models. The source was observed during four days in April 2017 with the Event Horizon Telescope at 230 GHz, including the phased Atacama Large Millimeter/submillimeter Array (ALMA), at an angular resolution of ∼20 μas (at a redshift of z = 0.536 this corresponds to ∼0.13 pc ∼ 1700 Schwarzschild radii with a black hole mass MBH = 8 × 108 M⊙). Imaging and model-fitting techniques were applied to the data to parameterize the fine-scale source structure and its variation. We find a multicomponent inner jet morphology with the northernmost component elongated perpendicular to the direction of the jet, as imaged at longer wavelengths. The elongated nuclear structure is consistent on all four observing days and across different imaging methods and model-fitting techniques, and therefore appears robust. Owing to its compactness and brightness, we associate the northern nuclear structure as the VLBI “core”. This morphology can be interpreted as either a broad resolved jet base or a spatially bent jet. We also find significant day-to-day variations in the closure phases, which appear most pronounced on the triangles with the longest baselines. Our analysis shows that this variation is related to a systematic change of the source structure. Two inner jet components move non-radially at apparent speeds of ∼15 c and ∼20 c (∼1.3 and ∼1.7 μas day−1, respectively), which more strongly supports the scenario of traveling shocks or instabilities in a bent, possibly rotating jet. The observed apparent speeds are also coincident with the 3C 279 large-scale jet kinematics observed at longer (cm) wavelengths, suggesting no significant jet acceleration between the 1.3 mm core and the outer jet. The intrinsic brightness temperature of the jet components are ≲1010 K, a magnitude or more lower than typical values seen at ≥7 mm wavelengths. The low brightness temperature and morphological complexity suggest that the core region of 3C 279 becomes optically thin at short (mm) wavelengths.Key words: galaxies: active / galaxies: jets / galaxies: individual: 3C 279 / techniques: interferometric⋆ The data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/640/A69 and at https://eventhorizontelescope.org/for-astronomers/data⋆⋆ Deceased.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Substructure in the stellar halo near the Sun: I. Data-driven clustering in integrals-of-motion space

Context. Merger debris is expected to populate the stellar haloes of galaxies. In the case of the Milky Way, this debris should be apparent as clumps in a space defined by the orbital integrals of motion of the stars. Aims. Our aim is to develop a data-driven and statistics-based method for finding these clumps in integrals-of-motion space for nearby halo stars and to evaluate their significance robustly. Methods. We used data from Gaia EDR3, extended with radial velocities from ground-based spectroscopic surveys, to construct a sample of halo stars within 2.5 kpc from the Sun. We applied a hierarchical clustering method that makes exhaustive use of the single linkage algorithm in three-dimensional space defined by the commonly used integrals of motion energy E, together with two components of the angular momentum, L z and L ⊥ . To evaluate the statistical significance of the clusters, we compared the density within an ellipsoidal region centred on the cluster to that of random sets with similar global dynamical properties. By selecting the signal at the location of their maximum statistical significance in the hierarchical tree, we extracted a set of significant unique clusters. By describing these clusters with ellipsoids, we estimated the proximity of a star to the cluster centre using the Mahalanobis distance. Additionally, we applied the HDBSCAN clustering algorithm in velocity space to each cluster to extract subgroups representing debris with different orbital phases. Results. Our procedure identifies 67 highly significant clusters (> 3σ), containing 12% of the sources in our halo set, and 232 subgroups or individual streams in velocity space. In total, 13.8% of the stars in our data set can be confidently associated with a significant cluster based on their Mahalanobis distance. Inspection of the hierarchical tree describing our data set reveals a complex web of relations between the significant clusters, suggesting that they can be tentatively grouped into at least six main large structures, many of which can be associated with previously identified halo substructures, and a number of independent substructures. This preliminary conclusion is further explored in a companion paper, in which we also characterise the substructures in terms of their stellar populations. Conclusions. Our method allows us to systematically detect kinematic substructures in the Galactic stellar halo with a data-driven and interpretable algorithm. The list of the clusters and the associated star catalogue are provided in two tables available at the CDS.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

High open circuit voltages of solar cells based on quantum dot and dye hybrid-sensitization

A type of solar cell based on quantum dot (QD) and dye hybrid-sensitized mesoporous TiO{sub 2} film electrode was designed and reported. The electrode was consisted of a TiO{sub 2} nanoparticle (NP) thin film layer sensitized with CdS quantum dot (QD) and an amorphous TiO{sub 2} coated TiO{sub 2} NP thin film layer that sensitized with C106 dye. The amorphous TiO{sub 2} layer was obtained by TiCl{sub 4} post-treatment to improve the properties of solar cells. Research showed that the solar cells fabricated with as-prepared hybrid-sensitized electrode exhibited excellent photovoltaic performances and a fairly high open circuit voltage of 796 mV was achieved.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Experimental determination of vacuum-level band alignments of SnS-based solar cells by photoelectron yield spectroscopy

Energy band offsets of SnS-based solar cell structure using various n-type semiconductors, such as CdS, SnS{sub 2}, In{sub 2}S{sub 3}, ZnIn{sub 2}Se{sub 4}, ZnO, and Mg{sub 0.3}In{sub 0.7}O, are evaluated by photoelectron yield spectroscopy. The valence band discontinuities are estimated to be 1.6 eV for both SnS/CdS and SnS/SnS{sub 2}, 0.9 eV for SnS/In{sub 2}S{sub 3}, 1.7 eV for SnS/ZnIn{sub 2}Se{sub 4}, and 1.8 eV for both SnS/ZnO and SnS/Mg{sub 0.3}Zn{sub 0.7}O. Using the valence band discontinuity values and the corresponding energy bandgaps of the layers, energy band diagrams are developed. This study implied a type-I heterostructure, appropriate for SnS-based solar cell, for the ZnIn{sub 2}Se{sub 4} or Mg{sub x}Zn{sub 1−x}O (0 ≤ x ≤ 0.3) interface and type-II for other junctions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

CdCl{sub 2} treatment related diffusion phenomena in Cd{sub 1−x}Zn{sub x}S/CdTe solar cells

Utilisation of wide bandgap Cd{sub 1−x}Zn{sub x}S alloys as an alternative to the CdS window layer is an attractive route to enhance the performance of CdTe thin film solar cells. For successful implementation, however, it is vital to control the composition and properties of Cd{sub 1−x}Zn{sub x}S through device fabrication processes involving the relatively high-temperature CdTe deposition and CdCl{sub 2} activation steps. In this study, cross-sectional scanning transmission electron microscopy and depth profiling methods were employed to investigate chemical and structural changes in CdTe/Cd{sub 1−x}Zn{sub x}S/CdS superstrate device structures deposited on an ITO/boro-aluminosilicate substrate. Comparison of three devices in different states of completion—fully processed (CdCl{sub 2} activated), annealed only (without CdCl{sub 2} activation), and a control (without CdCl{sub 2} activation or anneal)—revealed cation diffusion phenomena within the window layer, their effects closely coupled to the CdCl{sub 2} treatment. As a result, the initial Cd{sub 1−x}Zn{sub x}S/CdS bilayer structure was observed to unify into a single Cd{sub 1−x}Zn{sub x}S layer with an increased Cd/Zn atomic ratio; these changes defining the properties and performance of the Cd{sub 1−x}Zn{sub x}S/CdTe device.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Synthesis of CdS/CdSe core/shell ultra small nanostructures using new microwave assisted ultrasonic sol gel route

Core-shell CdS/CdSe nanostructures have been synthesized by new microwave assisted ultrasonic sol gel route. The solution was obtained by dissolving cadmium acetate and Thiourea in the molar ratio 1:1 in Triethlioamine. The solution was Ultrasonically irradiated by Ultrasonic crystal at 40 Hz for 3 hours at 70°C. The sol was kept for another 24 hours for gel formation. Selenium dioxide was used as a selenium source and added separately. The gel was spin coated on Quartz and Glass slides followed by microwave heat treatment. The samples were characterized by structural morphological and optical characterization. XRD studies confirm the zinc blende phase of the CdS nanoparticles. The mean nanocrystal sizes calculated using Scherrer equation is ∼1.2nm. Optical studies show the strong blue shift in the spectra due to very small size of the nanocrystals. TEM and HRTEM confirm the formation of core shell structures.

77 NANOSCIENCE AND NANOTECHNOLOGY↗