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THE INVESTIGATION OF ALTERNATIVE METALS OF Au, Ag, Al AND Cu FOR BACK CONTACT USED IN FABRICATED ZnS/SnS HETEROJUNCTION FOR SOLAR CELL APPLICATION

THE INVESTIGATION OF ALTERNATIVE METALS OF Au, Ag, Al AND Cu FOR BACK CONTACT USED IN FABRICATED ZnS/SnS HETEROJUNCTION FOR SOLAR CELL APPLICATION

Fabrication of thin Molybdenum backed target using rolling method

A successful attempt was made to fabricate a thin foil of natural Mo target on a thick Au backing with Indium in between to improve adhesion between the foils. Rolling at elevated temperature was considered to fabricate Mo foil while gold foil was fabricated employing conventional rolling technique. The heating of Mo foil under natural environment lead to the oxidation or carbonization on foil surface which was confirmed through Energy Dispersive X-ray Spectroscopy (EDS) measurements. Indium of thickness ∼86μg/cm2 was evaporated on Mo foil to improve adhesion between Mo and Au foils. The characterization of fabricated thin Mo foil was done using the Energy Dispersive X-ray Spectroscopy (EDS) and the Scanning Electron microscope (SEM) techniques. Thickness measurement of the target (Mo-Au) was done using Energy Dispersive X-ray Fluorescence (EDXRF) technique, in the measurements the thickness of the Mo foil and of gold backing are found out to be 1.3 mg/cm2 and 9 mg/cm2 respectively.

Quasi-ohmic contact formation assisted by the back contact with Cu2Te nanoparticles@reduced graphene oxide composites for highly efficient CdTe solar cells

Composite materials based on reduced graphene oxide decorated with cuprous telluride nanoparticles (Cu2Te NPs@rGO) were fabricated using a facilitated two-step method. A back-contact layer was formed using a spin-coating method for cadmium telluride (CdTe) solar cells. This research is aimed to improve the photovoltaic performance of a device containing Cu2Te NPs@rGO/Au back contacts. Cu2Te NPs, as the active copper diffusion source, dope and passivate the interfaces and grain boundaries of CdTe to form the p+-layer, which can reduce the recombination centers and back-contact barrier height. Simultaneously, the reduced graphene oxide (rGO), as a buffer and carrier transport layer, prevents excessive copper diffusion during the annealing process and improves the hole collection capacity. The p-type layer formed by the rGO contact with the Au film enhances hole transport and facilitates a low-resistance contact formation, forming a quasi-ohmic contact, and increases the open-circuit voltage and short-circuit current density. Cu2Te NPs@rGO/Au back contacts significantly improved the photovoltaic performance (Eff: 16.5%, Voc: 830 mV, Jsc: 27.13 mA/cm2, fill factor: 73.3%, area: 0.24 cm2). The composites retain properties of Cu2Te NPs and rGO. Their multifunctional properties reveal the potential of Cu2Te NPs@rGO as the back contact and broaden the application of graphene-based composites in photovoltaic devices. Additionaly, the preparation of graphene-based composites and their application as back contact is simple and convenient.

Air-Bridge Si Thermophotovoltaic Cell with High Photon Utilization

Thermophotovoltaic (TPV) cells convert photons emitted from hot surfaces into electrical power. Unlike solar cells, TPV cells can be placed in close proximity to the heat source, allowing below-bandgap (i.e., out-of-band, OOB) photons to be reflected and reabsorbed by the emitter. As the reflectance of OOB photons approaches unity, the spectral efficiency of the TPV becomes increasingly insensitive to the bandgap of the cell and the source temperature. Here, we employ air-bridge structures with a lateral junction Si TPV cell as a means of increasing OOB reflectivity, which allows for efficient operation at low thermal source temperatures that were long inaccessible to efficient Si TPV power generation. The devices exhibit an OOB reflectance of 98.0 ± 0.1% and an air-bridge scalability to at least 6 cm × 6 cm. Compared to devices with a Au back surface reflector (BSR), devices featuring an air-bridge BSR exhibit a 25% relative increase in power conversion efficiency at a thermal source temperature of 1988 K. Such performance improvements in TPV cells made with scalable and relatively low-cost Si can potentially expedite the widespread use of TPV systems in both energy storage and generation systems.

High performance low-bandgap (0.8 eV) single junction GaInNAsSb solar cells incorporating Au-based back surface reflectors

Low-bandgap GaInNAsSb single junction solar cells incorporating a planar Au back surface reflector for enhancing the photocurrent generation are reported. In particular, a 700 nm thick GaInNAsSb junction with a bandgap of 0.78 eV (corresponding to 6.2% N) incorporating the back reflector exhibited a short-circuit current density of 15.2 mA/cm2 for AM1.5D (1000 W/m2) illumination, when placed underneath a GaAs-filter mimicking the operation of a multijunction architecture. The corresponding external quantum efficiency represents the highest external quantum efficiency reported so far for dilute nitride solar cells with bandgaps below 0.8 eV. Electrical simulations reveal that the relatively high value of the quantum efficiency is attributed to a low p-type carrier concentration and partially to the varying doping level in the GaInNAsSb region. Moreover, the absorption coefficients for low-bandgap GaInNAsSb materials are estimated and used in a comprehensive optical analysis to understand the photon harvesting performance of the solar cells with reflector. The analysis reveals incomplete absorption in the GaInNAsSb layers for the double-pass configuration enabled by the planar back reflector pointing to the need for deploying more advanced structured reflectors. However, the structures exhibited high collection efficiencies laying the foundation for further improvements of the quantum efficiency values. Moreover, the low-bandgap dilute nitride solar cells show potential to meet the current-matching requirements in next-generation multijunction devices with five or more junctions, thus being a prospective alternative for replacing Ge as the bottom junction.

It's Complicated: On Relativistic Effects and Periodic Trends in the Melting and Boiling Points of the Group 11 Coinage Metals.

While the color of metallic gold is a prominent and well-investigated example for the impact of relativistic effects, much less is known regarding the influence on its melting and boiling point (MP/BP). To remedy this situation, this work takes on the challenging task of exploring the phase transitions of the Group 11 coinage metals Cu, Ag, and Au through nonrelativistic (NR) and scalar/spin-orbit relativistic (SR/SOR) Gibbs energy calculations with λ-scaled density-functional theory (λDFT). At the SOR level, the calculations provide BPs in excellent agreement with experimental values (1%), while MPs exhibit more significant deviations (2-10%). Comparing SOR calculations to those conducted in the NR limit reveals some remarkably large and, at the same time, some surprisingly small relativistic shifts. Most notably, the BP of Au increases by about 800 K due to relativity, which is in line with the strong relativistic increase of the cohesive energy, whereas the MP of Au is very similar at the SOR and NR levels, defying the typically robust correlation between MP and cohesive energy. Eventually, an inspection of thermodynamic quantities traces the trend-breaking behavior of Au back to phase-specific effects in liquid Au, which render NR Au more similar to SOR Ag, in line with a half-a-century-old hypothesis of Pyykkö.

Fabrication of the gold (Au) backed [formula omitted] targets for in-beam gamma-ray spectroscopy

The isotopically enriched T130e targets of ~ 1.2 mg/cm2 thickness were fabricated on 4–6 mg/cm2 gold (Au) backing. The vapor deposition method was employed using the resistive heating technique. To minimize the material consumption and increase the deposition efficiency, an indigenously developed graphite crucible with 1 mm opening was used to deposit T130e metal powder at a minimum source to substrate distance of 2 cm. A heat shield was placed at 1 cm above the graphite crucible to dissipate the heat. The fabrication of these targets were successfully achieved by using 10 mg of metal powder in each evaporation. The fabricated targets were characterized by using X-ray Fluorescence (XRF) measurements, Energy Dispersive X-ray Spectroscopy (EDS) and Scanning Electron Microscope (SEM). An experiment to study the nuclear structure via in-beam γ-ray spectroscopy was preformed using one of the fabricated T130e targets. The T130e(B9e,xn) reaction was used to populate the intermediate and high-spin states of Ba isotopes with B9e beam at 36- and 48 MeV lab energy. The relative percentage (%) cross-sections were measured for the B134−136a nuclei and found to be in agreement with the PACE4 calculations.

Numerical optimization of 0.5‐μm‐thick Cu (In1-xGax) Se2 solar cell

This paper presents a numerical simulation of 2D ultra-thin Cu (In1-xGax) Se2 solar cell under drift-diffusion transport across heterojunction interfaces. The validation of the CIGS model is performed by matching the electrical characteristics of the experimental and simulation results. The surface recombination velocity of CdS/CIGS heterojunction interface and element composition Ga/(In + Ga) ratio effect on the optical properties and electrical performances of CIGS absorber are investigated. The thickness dependence and carrier concentration of the semiconductor layers on the cell performance are investigated. The nanostructured Ag, Au, or Cu back mirror is used to replace conventional Mo back contact to improve light absorption in the ultra-thin CIGS layer. Best power conversion efficiency of 21.74% has been obtained with a thinner absorber of about 0.5‐μm‐thick under AM1.5 illumination condition, 300 K.

Study of ultra-thin CdTe/CdS heterostructure solar cell purveying open-circuit voltage ∼1.2 V

This study focuses on aiming higher stabilized sunlight to electricity conversion efficiency for Cadmium Telluride (CdTe) absorber based solar cell. Common CdTe solar cell with Au back or Zinc Telluride (ZnTe) back surface field (BSF) with Cu back metal has voltages < 1V. The reason behind this low voltage has been investigated in details. In this report, simulation yielding of (M = Cu, Ni, Au, Ir, Pd, and Pt) thin-film solar cell (TFSC) has been presented. The solar cell has been modelled and analyzed using Analysis of Microelectronic and Photonic Structures – 1 Dimensional (AMPS-1D) device simulator for various back metals with work function, Φm ≥ 5 eV. The thickness was varied from 100–1800 nm, and from 15–100 nm for the active p-CdTe absorber, and n-Cadmium Sulphide (CdS) window layers, respectively, to optimize the device depth. Meanwhile, the donor and acceptor concentration was varied to outline their effects on photovoltaic (PV) parameters. The utmost efficiency (η) of ∼30% along with open circuit voltage of 1.194 V, short circuit current density of 28.6 mA cm−2, and fill factor (FF) of 89.3% has been achieved ideally with Platinum (Pt) back contact at (111) plane under standard test conditions (STC) of and 1 Sun illumination (1000 W m−2) at air mass (AM) 1.5. Lastly, the cell operating temperature was varied from to to verify the thermal stability of the proposed structure. Present work provides a guideline to select back metal in CdTe solar cell. Our proposed solar cell offers the prospect of being a highly efficient cost effective second generation (2G) TFSC.

Thin-Film Architectures with High Spectral Selectivity for Thermophotovoltaic Cells

Thermophotovoltaic (TPV) systems are a promising technology for distributed conversion of high-temperature heat to electricity. To achieve high conversion efficiency, the transport of sub-bandgap radiation between the thermal emitter and PV cell should be suppressed. This can be achieved by recycling sub-bandgap radiation back to the emitter using a spectrally selective cell. However, conventional TPV cells exhibit limited sub-bandgap reflectance. Here we demonstrate thin-film In0.53Ga0.47As-based structures with high spectral selectivity, including record-high average sub-bandgap reflectance (96%). Selectivity is enabled by short optical paths through a high-quality material fabricated using epitaxial lift-off, high-reflectance back surfaces, and optimized interference. In addition, we use a parallel-plate TPV model to evaluate the impact of specific structural features on performance and to optimize the cell architecture. We show that a dielectric spacer between InGaAs and the Au back surface is an impo...

Material-assisted metamaterial: a new dimension to create functional metamaterial

A high Q-value reflective type metasurface consisting of 1D Au nanorods, a SiO2 spacer and a Au back reflector is demonstrated. It is shown that the sideband of the resonant mode can be suppressed as the resonant wavelength close to the phonon absorption of SiO2. By combining both designed structured resonance and inherent property of the based materials, a low angle-dependent metasurface with a Q-value of 40 has been demonstrated. The proposed structure will be useful for high sensitivity sensing and narrow band thermal emitter.

Embedded nanowire window layers for enhanced quantum efficiency in window-absorber type solar cells like CdS/CdTe

Embedded CdS nanowires are used for improving the spectral transmission of the CdS window layer, thus enhancing the quantum efficiency of CdS–CdTe solar cells. Substantially higher light transmission is observed in the 300nm–550nm wavelength range. A nearly ideal spectral response of quantum efficiency over a wide spectral range provides evidence for improved light transmission through the window layer and enhanced absorption and carrier generation in the CdTe absorber layer. Nanowire CdS/CdTe solar cells on SnO2/ITO-soda lime glass substrates, and with Cu/graphite paste/silver paste as back contact electrodes, yield a power conversion efficiency of 12%. MoO3−x /Au back contacts were also investigated. With these back contacts, the nanowire CdS–CdTe solar cells exhibit efficiency comparable to the efficiency of their planar CdS counterparts. Junction transport mechanisms are delineated for advancing the basic understanding of device physics at the interface. Our results prove the efficacy of this nanowire approach for enhancing the quantum efficiency in window-absorber type solar cells (CdS–CdTe, CdS–CIGS and CdS–CZTSSe etc.) and other optoelectronic devices.

The effect on CdS/CdTe solar cell conversion efficiency of the presence of fluorine in the usual CdCl2 treatment of CdTe

The addition of CdF2 to the CdCl2 solution used in the well-known CdCl2 treatment of CdS/CdTe solar cells has been observed to drastically improve the conversion efficiency of fully fabricated CdS/CdTe solar cells. The observed improvement is as a result of further enhancement of structural and optoelectronic properties of the CdCl2 + CdF2-treated CdTe layers compared to the CdCl2-treated CdTe layers. A set of CdS/CdTe samples were grown by electrochemical deposition under different conditions and each sample was divided into two. One set of these parts was treated with only CdCl2 solution while the other set was treated with the CdCl2 + CdF2 mixture. Both sets were annealed at 450 °C for 15 min and the solar cells completed by evaporating Au back contact on the CdTe layers after chemical etching. The results of the device measurements show drastic improvements in all the solar cell parameters (open-circuit voltage, short-circuit current density, fill factor and conversion efficiency) for the devices treated with CdCl2 + CdF2 mixture compared to those treated with only CdCl2. The conversion efficiencies increased from (1.0–3.0)% with CdCl2 treatment to about (5.0–7.0)% with CdCl2 + CdF2 treatment. The observed improvements have been attributed to the unique properties of fluorine.

Enhancement of current collection in epitaxial lift-off InAs/GaAs quantum dot thin film solar cell and concentrated photovoltaic study

We report the fabrication of a thin film InAs/GaAs quantum dot solar cell (QD cell) by applying epitaxial lift-off (ELO) approach to the GaAs substrate. We confirmed significant current collection enhancement (∼0.91 mA/cm2) in the ELO-InAs QD cell within the wavelength range of 700 nm–900 nm when compared to the ELO-GaAs control cell. This is almost six times of the sub-GaAs bandgap current collection (∼0.16 mA/cm2) from the wavelength range of 900 nm and beyond, we also confirmed the ELO induced resonance cavity effect was able to increase the solar cell efficiency by increasing both the short circuit current and open voltage. The electric field intensity of the resonance cavity formed in the ELO film between the Au back reflector and the GaAs front contact layer was analyzed in detail by finite-differential time-domain (FDTD) simulation. We found that the calculated current collection enhancement within the wavelength range of 700 nm–900 nm was strongly influenced by the size and shape of InAs QD. In addition, we performed concentrated light photovoltaic study and analyzed the effect of intermediate states on the open voltage under varied concentrated light intensity for the ELO-InAs QD cell.

Efficient photon extraction from a quantum dot in a broad-band planar cavity antenna

We analyse the extraction of photons emitted from single InAs quantum dots embedded in planar microcavities. The structures are designed to achieve broad-band operation and high-collection efficiency from a device requiring straightforward fabrication, even with electrical contacts. The designs consist of a quantum dot in a GaAs membrane with asymmetric top and bottom mirrors and a top-side solid immersion lens (SIL). Four separate cases are considered in our design: a GaAs membrane only (case 1), GaAs membrane with a glass SIL on top (case 2), a GaAs membrane with a glass SIL on top and a back mirror consisting of Au (case 3), a GaAs membrane with a glass SIL on top of a distribute Bragg reflector mirror and Au back mirror (case 4). Both finite difference time domain and analytical simulations are used to calculate the electric field, power density, and far-field radiation pattern. For optimized structures (case 4), we obtain significant extraction efficiencies (&amp;gt;50%) with modest Purcell enhancements (∼20%) and a large spectral full-width-half-maximum (&amp;gt;100 nm). The high-extraction efficiency, broad-band operation, and facile fabrication make the proposed structures promising for realistic quantum dot devices.

Formation of Hierarchically Structured Thin Films

AbstractHere, we report the preparation of hierarchically structured polymer brushes with well‐defined geometries via multiple step microcontact printing (MS‐µCP) of inks containing different ratios of initiator‐terminated thiols and non‐reactive alkylthiols. Thick (and dense), polymer brushes grew from self‐assembled monolayers (SAMs) with high concentration of initiator‐terminated thiols, and these brushes exhibited high chemical etch‐resistance, compared to thin (and less dense), brushes grown from more dilute initiator‐terminated SAMs. Upon etching, patterned crosslinking polymer brush films decorated with thin layers of Au, could be lifted off the surface to form geometrically well‐defined free‐standing hierarchical films. These polymer brush films showed interesting buckling instabilities when compressed. Areas with different brush thicknesses and Au backing showed markedly different buckling behavior, leading to unusual patterns of wrinkles with different wavelengths and orientations toward the force field.

Improvement of thickness and uniformity of isotopically enriched 12C targets on backings by the HIVIPP method

We have made enriched 12C targets to accurately measure the cross-section of the 12C( α, γ) 16O reaction, which is very important in nuclear astrophysics. Isotopically enriched 12C targets for studying this small cross-section, especially for use with an intense pulsed α beam was desired to meet the following requirements: (1) use of impurity-free enriched 12C, (2) stability for a long time measurement and (3) uniform thickness in the range 200–300 μg/cm 2. To meet these experimental requirements, isotopically enriched amorphous 12C powder was converted into graphite powder in an electric furnace at a temperature of 3000 K and subsequently the graphite powder was deposited on a thick Au backing via the HIVIPP method. Targets thus prepared could be made thicker than 200 μg/cm 2. They had a good uniformity and a very high stability against irradiation with high intensity ion beams.

Simultaneous production of high specific activity 64Cu and 61Co with 11.4 MeV protons on enriched 64Ni nuclei

The 64Cu and 61Co radionuclides were produced simultaneously by irradiation of enriched 64Ni on a low energy proton-only cyclotron. Nickel targets were prepared by electrodeposition of enriched 64Ni (>95%) on Au backing at thicknesses of 25–225 mg/cm 2 with efficiencies >99%. Irradiations up to 30 μA for 8 h were performed with 11.4 MeV protons using a water-cooled target mounting. Radiochemical separation of 64Cu and 61Co from 64Ni was performed by chromatography of the chlorocomplexes in a single step using an anion exchange resin column with a yield >95%. Using this method, the Ni target material was recovered and re-plated for subsequent production runs with an overall efficiency >96%. The excitation function for the 64Ni(p,n) 64Cu reaction was measured and compared with published values. Experimental thick target saturation yields of 159 mCi/μA for 64Cu and 715 μCi/μA for 61Co were achieved. Typical specific activities of 64Cu were found to be 18.8±3.3 Ci/μmol.

Vertical-cavity amplifying photonic switch at 1.5 μm

The development of a fast amplifying switch operating at 1.55-μm wavelength is of particular interest as the active element in optical communication systems. We report the first vertical-cavity amplifying photonic switch (VCAPS) at 1.55-μm wavelength, with a 14-dB gain and 10-ps commutation time. This structure is fabricated by the epitaxial lift-off technique and is composed of a resonant periodic gain multiple quantum wells active layers sandwiched between a SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -Au back mirror based on a Si substrate and a Si-SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> front mirror.

Dithiocarbamate Extraction and Au(III) Back Extraction for Determination of Mercury in Water and Biological Samples by Anodic Stripping Voltammetry

A novel method employed for determining trace mercury in water and biological samples was developed in the study. The mercury was preconcentrated from the water samples and the digested biological samples through means of diethyldithiocarbamate extraction in conjunction with Au 3+ back extraction. The preconcentrated solution, with simply contained the enriched mercury ion with the possible transition-metal ions and nonreacted Au 3+ 3+, was next transferred to an electrochemical cell for detecting mercury via differential pulse anodic stripping voltammetry (DPASV) throught the usage of a gold film carbon electrode