Ag Alloying Research Articles

Effect of Ag alloying and trace precipitation on corrosion resistance of Ti-Ta-Ag ternary alloy.

This work systematically analysed the electrochemical and corrosion behaviour of Ti-Ta-Ag ternary alloy samples in Hank's solution. For the samples with 1.5% and 3% Ag content, the sintering temperature increased from 750 to 950°C, and the corresponding corrosion resistance increased by 100 times due to the increased alloying of Ag; meanwhile for the sample with 4.5% Ag content, the sintering temperature increased from 750 to 950°C, and the corresponding corrosion resistance decreased by six times due to the increased precipitation of Ag. These tests prove that the Ag alloying is beneficial to the enhancement of the corrosion resistance of Ti-Ta-Ag ternary alloy, but the Ag trace precipitation has the opposite effect. A series of electrochemical characterizations and density functional theory calculations explain the mechanism of the above phenomenon. Ag alloying can promote the formation of uniform, complete, dense, stable and thick passivation layer on the surface of Ti-Ta-Ag ternary alloy, which makes Ti-Ta-Ag ternary alloy uniformly corroded without pitting. In addition, Ag alloying can effectively reduce the contact resistance of the solid–liquid interface. However, the trace precipitation of Ag plays the opposite role to the above effect.

Enhanced Power Factor and Figure of Merit of Cu2ZnSnSe4-Based Thermoelectric Composites by Ag Alloying.

The quaternary chalcogenide composites Cu2ZnSn1-xAgxSe4 (0 ≤ x ≤ 0.075) have been successfully synthesized by high-temperature melting and annealing followed by hot-pressing. The phase structure of the bulk sample has been analyzed by powder X-ray diffraction and Rietveld refinement combined with Raman spectroscopy to confirm Cu2ZnSnSe4 as the main phase with ZnSe and Cu5Zn8 secondary phases. The thermoelectric properties of all specimens have been investigated in the temperature range of 300-700 K. The replacement of Sn by Ag significantly enhances the electrical transport properties by providing extra charge carriers. The tremendous reduction in electrical resistivity enhances the power factor, and a maximum power factor of 804 μW K-2 m-1 is achieved at 673 K for the specimen with 5% Ag content. Furthermore, increased point defects increase phonon scattering, resulting in reduced thermal conductivity. The combined effect of improved power factor and suppressed thermal conductivity provides a good boost to the dimensionless figure of merit. The maximum figure of merit of zT = 0.25 has been achieved at 673 K for Cu2ZnSn0.95Ag0.05Se4, which is 2.5 times the value of the parent sample.

Sputtered Ag-alloyed Cu(In, Ga)(Se, S)2 solar cells by sequential process

A sequential route for low-cost fabrication of high quality Ag-alloyed CIGS absorbers is reported. Ag-alloying is introduced into the CuInGa precursor to widen the band gap and improve the crystallinity of the ACIGS absorbers. The morphological, compositional, and structural characteristics of the ACIGS absorber are also systematically investigated. Different Ag thin layer incorporation locations at the bottom, in the middle and on the top of CuInGa precursors are schemed for deep understanding the band gap energy and crystallinity regulation mechanism of Ag alloying. A conversion efficiency of 10.2% is achieved for the ACIGS device with Ag at the bottom. The notable Voc improvement can be obtained due to the widened band gap and the band gap gradient in the absorber created by the Ag and Ga elements grading. Finally, the ACIGS absorbers are further sulfurized and a highest power conversion efficiency of 13.01% is obtained. Our results indicate that the sequential magnetron sputtering is a promising way for the fabrication of CIGS thin film solar cells.

Alkali Dispersion in (Ag,Cu)(In,Ga)Se2 Thin Film Solar Cells-Insight from Theory and Experiment.

Silver alloying of Cu(In,Ga)Se2 absorbers for thin film photovoltaics offers improvements in open-circuit voltage, especially when combined with optimal alkali-treatments and certain Ga concentrations. The relationship between alkali distribution in the absorber and Ag alloying is investigated here, combining experimental and theoretical studies. Atom probe tomography analysis is implemented to quantify the local composition in grain interiors and at grain boundaries. The Na concentration in the bulk increases up to ∼60 ppm for [Ag]/([Ag] + [Cu]) = 0.2 compared to ∼20 ppm for films without Ag and up to ∼200 ppm for [Ag]/([Ag] + [Cu]) = 1.0. First-principles calculations were employed to evaluate the formation energies of alkali-on-group-I defects (where group-I refers to Ag and Cu) in (Ag,Cu)(In,Ga)Se2 as a function of the Ag and Ga contents. The computational results demonstrate strong agreement with the nanoscale analysis results, revealing a clear trend of increased alkali bulk solubility with the Ag concentration. The present study, therefore, provides a more nuanced understanding of the role of Ag in the enhanced performance of the respective photovoltaic devices.

Energy band alignment at the heterointerface between CdS and Ag-alloyed CZTS

Energy band alignment at the heterointerface between CdS and kesterite Cu2ZnSnS4 (CZTS) and its alloys plays a crucial role in determining the efficiency of the solar cells. Whereas Ag alloying of CZTS has been shown to reduce anti-site defects in the bulk and thus rise the efficiency, the electronic properties at the interface with the CdS buffer layer have not been extensively investigated. In this work, we present a detailed study on the band alignment between n-CdS and p-CZTS upon Ag alloying by depth-profiling ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). Our findings indicate that core-level peaks and the valence band edge of CdS exhibit a significant shift to a lower energy (larger than 0.4 eV) upon the etching of the CdS layer, which can be assigned due to band bending and chemical shift induced by a change in the chemical composition across the interface. Using a simplified model based on charge depletion layer conservation, a significantly larger total charge region depletion width was determined in Ag-alloyed CZTS as compared to its undoped counterpart. Our findings reveal a cliff-like band alignment at both CdS/CZTS and CdS/Ag-CZTS heterointerfaces. However, the conduction-band offset decreases by more than 0.1 eV upon Ag alloying of CZTS. The approach demonstrated here enables nanometer-scale depth profiling of the electronic structure of the p–n junction and can be universally applied to study entirely new platforms of oxide/chalcogenide heterostructures for next-generation optoelectronic devices.

Crystal Structure of Au30-xAgx(S-tBu)18 and Effect of the Ligand on Ag Alloying in Gold Nanomolecules.

We report the X-ray crystal structure of the Au30-xAgx(S-tBu)18 alloy and the effect of the ligand on alloying site preferences. Gold-silver nanoalloys prepared by co-reduction of metal salts are known to have only partial Ag occupancies. Interestingly, Au30-xAgx(S-tBu)18 has 100% Ag occupancy at two sites on the core surface as well as partial Ag occupancies on the surface, capping, and staples sites. The Au30-xAgx(S-tBu)18 (x = 1-5) composition was confirmed by X-ray diffraction and electrospray ionization mass spectrometry studies. Thiolate ligands can be categorized into three classes on the basis of the groups at the α-position as aliphatic, aromatic, and bulky thiols. The effect of the ligand on Ag doping can be clearly seen in the crystal structures of Au36-xAgx(SPh-tBu)24 and Au38-xAgx(SCH2CH2Ph)24 when compared with that of Au30-xAgx(S-tBu)18. Ag is preferentially doped onto the core surface when the ligand is aliphatic, and Ag is doped in both core surface and staple metal sites when the ligand is aromatic or bulky.

Ag alloying for modifications of carrier density and defects in Zn-rich (Ag,Cu)2ZnSnSe4 thin film solar cells

Abstract The Ag alloying Cu2ZnSnSe4 absorber has profound influences on the material properties including the carrier density, defects, grain structure and morphology, etc. It is found that Ag alloying could effective decrease the carrier density of Ag alloyed (Ag,Cu)2ZnSnSe4 (ACZTSe) absorbers and thus increase the depletion region width (DRW) of corresponding kesterite solar cells. At the same time, the CuZn related defects are decreased and consequently the band tailing and possible Fermi level pinning could be supressed. In addition, further adjusting [Zn]/[Sn] ratios in Zn-rich ACZTSe absorbers could be helpful to the performance of solar cells due to a fine modification of the carrier density and defects. After optimizing of chemical compositions by combining both modifications, the Ag alloyed Zn-rich ACZTSe based kesterite thin film solar cells have achieved the highest efficiency of 8.68%, in which the Ag alloying content with respected to [Ag]/([Ag]+[Cu]) and the [Zn]/[Sn] ratio are 10% and 1.14, respectively.

Homogeneous and Graded Ag Alloying in (Cu1‐xAgx)2ZnSnSe4 Solar Cells

Cu2ZnSn(S,Se)4 (CZTSSE)‐based solar cell performances are limited by band tailing due to a large amount of CuZn antisite defects. Partially replacing the Cu atoms by larger Ag ones can significantly reduce the prevalence of these defects, which are particularly detrimental close to the front interface. Herein, the possibility of synthesizing (Cu1‐xAgx)2ZnSnSe4 absorbers with various Ag contents by vacuum‐based processes is demonstrated. Although the synthesis of high‐quality materials is demonstrated, their use in thin film photovoltaic devices does not exhibit performance improvement compared with efficient pure CZTSSE‐based solar cells. Moreover, the comparison with literature data reopens the debate of the beneficial effect of homogeneous Ag alloying in kesterite. On the contrary, a new method is proposed to fabricate graded (Cu1‐xAgx)2ZnSnSe4 absorbers with increased Ag content at the interfaces. The solar cells with graded absorbers exhibit better performances than the reference Ag‐free ones. Particularly, improved current collection at the back contact and slight reduction of the front interface recombination are demonstrated.

Integrated, Flexible Lithium Metal Battery with Improved Mechanical and Electrochemical Cycling Stability

The success of beyond lithium-ion battery (LIB) technologies, i.e., Li oxygen and Li–S cells, depends in large part on the use of metallic anode materials. Metallic lithium, however, tends to grow parasitic dendrites, which would penetrate the separator to cause safety concerns. Moreover, the dendrites are highly reactive to carbonate electrolytes and invariably render a reduced Coulombic efficiency. Here, we propose our design of a dendrite blocking layer with size-tunable Ag nanoparticles (NPs) decorated on the mesoporous SiO2 nanospheres. The synergistic coupling of these complementary components enables the effective regulation of the lithium nucleation behavior via a protected Li–Ag alloying process. The Li plating/stripping process of a symmetric Ag NPs@SiO2-coated Li–metal cell exhibits a reduced voltage hysteresis, facile lithium nucleation process, and enhanced Coulombic efficiencies at various current densities. When the Ag NPs@SiO2-coated copper foil anode was integrated with lithium manganese ...

Comparison of Ag and Ga alloying in low bandgap CuInSe2-based solar cells

Solar cells based on CuInSe2 (CIS) with absorber bandgap 1.0 eV are excellent candidates for a bottom cell in a tandem solar cell. This work investigates the effect of alloys of Ag and small amounts of Ga as an approach to improve the efficiency of CIS-based solar cells with bandgap less than 1.1 eV. Ga and Ag influence the surface morphology of the absorber layer, and Ag alloyed solar cells also have an increased concentration of Ag relative to Cu at the surface. Despite these structural and compositional differences compared to CuInSe2, the device with the highest efficiency incorporates a mixture of Ga and Ag alloying to form (Ag,Cu)(In,Ga)Se2, where Ga addition improves the open circuit voltage and Ag addition improves the short circuit current. Ag improves current collection from long wavelength light due to the larger space charge width of Ag alloyed solar cells. However, Ag alloyed devices demonstrate lower VOC due to an interface recombination mechanism.

Systematic and Extensive Emission Tuning of Highly Efficient Cu–In–S-Based Quantum Dots from Visible to Near Infrared

Group I–III–VI chalcogenides are emerging candidates for the synthesis of efficient quantum dot (QD) emitters, particularly since they are free from environmentally harmful substances such as Cd, Pb, and As. Among them, Cu–In–S (CIS) and Cu–In–Se1–x–Sx (CISeS) are the most common compositions as visible and near-infrared (NIR) QD emitters, respectively. We herein explore efficient synthetic pathways to demonstrate extensively emission-tuned CIS QDs from visible to NIR with high photoluminescence quantum yields (PL QYs) of over 70%. To systematically tune PL, synthetic parameters of CIS core QDs are varied such as Cu/In molar ratio, core growth condition, Ag alloying, and In precursor change, whereas a highly reactive elemental sulfur is commonly adopted for core growth. Starting from visible CIS/ZnS QDs, whose emission is tuned in green (534 nm) to red (625 nm), depending on the Cu/In ratio, their emissions gradually shift in the PL peak to 744 nm by controlling the core growth condition to 806 nm by allo...

Stability enhancement of Cu2S against Cu vacancy formation by Ag alloying

As a potential solar absorber material, Cu2S has proved its importance in the field of renewable energy. However, almost all the known minerals of Cu2S suffer from spontaneous Cu vacancy formation in the structure. The Cu vacancy formation causes the structure to possess very high p-type doping that leads the material to behave as a degenerate semiconductor. This vacancy formation tendency is a major obstacle for this material in this regard. A relatively new predicted phase of Cu2S which has an acanthite-like structure was found to be preferable than the well-known low chalcocite Cu2S. However, the Cu-vacancy formation tendency in this phase remained similar. We have found that alloying silver with this structure can help to reduce Cu vacancy formation tendency without altering its electronic property. The band gap of silver alloyed structure is higher than pristine acanthite Cu2S. In addition, Cu diffusion in the structure can be reduced with Ag doped in Cu sites. In this study, a systematic approach is presented within the density functional theory framework to study Cu vacancy formation tendency and diffusion in silver alloyed acanthite Cu2S, and proposed a possible route to stabilize Cu2S against Cu vacancy formations by alloying it with Ag.

Highly efficient Ag-alloyed Cu(In,Ga)Se2 solar cells with wide bandgaps and their application to chalcopyrite-based tandem solar cells

In this work, Ag alloying effects in wide-bandgap Cu(In,Ga)Se2 (CIGS) solar cells are investigated, and their application in tandem solar cells is attempted. With a three-stage process, highly efficient Ag-alloyed CIGS (ACIGS) solar cells with Eg ≥ 1.4 eV are fabricated; the benefits of Ag alloying are discussed with a focus on the control of structural/electronic disorders. The ACIGS solar cells are found to exhibit particularly improved device performance in specific compositions; in general, Ag alloying helps to enhance VOC in wide-bandgap CIGS solar cells. With wide-bandgap ACIGS cells as a top subcell, various kinds of chalcopyrite-based tandem (two-junction and two-terminal) cells are demonstrated. Prospects and limitations of chalcopyrite-based tandem cells are investigated by examining beam-splitting tandem, mechanically stacked tandem, and monolithic tandem cells.

Structural and catalytic properties of the Au25-xAgx(SCH3)18 (x = 6, 7, 8) nanocluster.

In this study, we explore the structural, electronic and catalytic properties of bimetallic nanoparticles of the form Au25-xAgx(SR)18 (for x = 6, 7, 8). Due to the combinatorial enormity of the number of different alloyed structures, we choose 500 random configurations corresponding to each alloying level and energetically optimize their structures. Here we report the properties of the lowest energy structures and determine the most favorable Ag alloying sites for these systems. We also show that nanoalloys with one Ag at the center and the rest in the outer shell of the Au13 kernel are less energetically favorable than the ones with all the Ag atoms occupying the surface of the Au13 kernel. We further present experimental results showing that catalytic oxidation of CO is adversely affected due to Ag alloying. We provide qualitative and quantitative evidence to explain this reduction of the catalytic activity using Fukui functions and average adsorption energies respectively.

Enhancing Open-Circuit Voltage of Solution-Processed Cu2ZnSn(S,Se)4 Solar Cells With Ag Substitution

Cation substitution is a promising approach to improve the efficiency of kesterite solar cells. Here, silver has been introduced into Cu2ZnSn(S,Se)4 (CZTSSe) thin film to replace Cu partially and form (Ag x Cu1− x )2ZnSn(S,Se)4 (ACZTSSe) through a cost-effective dimethyl sulfoxide-based solution method. Fundamental properties of the mixed Ag–Cu kesterite compound as a function of the Ag/(Ag + Cu) ratio were investigated. It is demonstrated that the varying Ag content significantly impacts the band gap and crystal structure of ACZTSSe thin films. Furthermore, a remarkable decreasing trend in the intrinsic hole concentration accompanies the increasing Ag incorporation, which eventually leads to a doping-type conversion in high Ag containing layers. The changing bulk properties of absorber layers due to the Ag alloying have strong influences on device performance. Benefiting from the enhanced V OC, the power conversion efficiency is improved from 4.77% for the baseline CZTSSe cell to 7.12% for an ACZTSSe device containing 16% Ag, and about a 30 mV smaller V OC deficit is achieved. The V OC enhancement evidences that the solution method is facile and viable to achieve proper cation substitution toward higher efficiency kesterite solar cells.

Substitution of Li for Cu in Cu2ZnSnS4: Toward Wide Band Gap Absorbers with Low Cation Disorder for Thin Film Solar Cells.

The substitution of lithium for copper in Cu2ZnSnS4 (CZTS) has been experimentally and theoretically investigated. Formally, the (Cu1-xLix)ZnSnS4 system exhibits two well-defined solid solutions. Indeed, single crystal structural analyses demonstrate that the low (x < 0.4) and high (x > 0.6) lithium-content compounds adopt the kesterite structure and the wurtz-kesterite structure, respectively. For x between 0.4 and 0.6, the two aforementioned structure types coexist. Moreover, 119Sn NMR analyses carried out on a (Cu0.7Li0.3)2ZnSnS4 sample clearly indicate that lithium replaces copper preferentially on two of the three available 2-fold crystallographic sites commonly occupied by Cu and Zn in disordered kesterite. Furthermore, the observed individual lines in the NMR spectrum suggest that the propensity of Cu and Zn atoms to be randomly distributed over the 2c and 2d crystallographic sites is lowered when lithium is partially substituted for copper. Additionally, the first-principles calculations provide insights into the arrangement of Li atoms as a function of the Cu/Zn disorder and its effect on the structural (lattice parameters) and optical properties of CZTS (band gap evolution). Those calculations agree with the experimental observations and account for the evolutions of the unit cell parameters as well as for the increase of band gap when the Li-content increases. The calculation of the formation enthalpy of point defect unambiguously indicates that Li modifies the Cu/Zn disorder in a manner similar to the change of Cu/Zn disorder induced by Ag alloying. Overall, it was found that Li alloying is a versatile way of tuning the optoelectronic properties of CZTS making it a good candidate as wide band gap materials for the top cells of tandem solar cells.

Ag incorporation in low-temperature grown Cu(In,Ga)Se2 solar cells using Ag precursor layers

In this work, with Ag alloying, we attempted to improve the microstructure and device performance of low-temperature grown Cu(In,Ga)Se2 (CIGS) solar cells. Ag precursors with various thicknesses are deposited onto Mo prior to the CIGS growth step, and absorber films are formed via a single-step co-evaporation at a substrate temperature of 350°C. The addition of Ag in low-temperature grown CIGS films induces significant recrystallization and Na incorporation. Through adjustment of the Ag content of the Ag-alloyed CIGS films, an improved device performance is obtained compared with a CIGS solar cell without Ag alloying.

Enhancement of L21 order and spin-polarization of Heusler alloy Co2MnSi thin film by Ag alloying

We report enhancement of L21 order and the resultant improvement of spin polarization of Co2MnSi (CMS) Heusler alloy thin films by a small amount of Ag alloying (xAg⩽4.5 atomic (at.) %). The degree of L21 order in CMS increases with xAg(=2.7at.% and 4.5at.%), which shows a positive correlation with the magnitude of negative anisotropic magnetoresistance ratio, suggesting the enhancement of spin polarization. Since the benefit of Ag-doping was confirmed even at low annealing temperature around 350°C, this method could be useful for processing spintronic devices using Heusler alloys at relatively low annealing or substrate temperature.

Enhanced hydrogen storage properties of a Mg–Ag alloy with solid dissolution of indium: a comparative study

Both thermodynamics and kinetics of the Mg5.7In0.3Ag–H2 system were significantly destabilized by combining Ag alloying with In dissolution.

Glass-forming ability, crystallization kinetics, mechanical property, and corrosion behavior of Zr–Al–Ni–Ag glassy alloys

The effects of partial substitution of Ni by Ag in Zr56Al16(Ni1−xAgx)28 (at.%, x=0, 0.1, 0.2, 0.3, and 0.4) alloys on their glass-forming ability (GFA), crystallization kinetics, mechanical property, and corrosion behavior were investigated. The critical diameter for glass formation of Zr56Al16Ni28 alloy is significantly enhanced by partially substituting Ag for Ni. The Zr56Al16(Ni0.7Ag0.3)28 BMG exhibits the best GFAand its critical diameter for glass formation is 20mm. Ag-bearing Zr-based BMG presents a lower Avrami exponent n than that of Ag-free Zr–Al–Ni BMG, indicating the nucleation rate is reduced by the addition of Ag. The corrosion resistance of Zr–Al–Ni BMG is improved by Ag alloying, and the Zr–Al–Ni–Ag BMG exhibits higher corrosion resistance than that of other known Zr-based BMGs with high GFA. Moreover, the BMGs possess high compressive yield strength of 1830–2000MPa, large plastic strain of 2.7–3.1%, and high specific strength of 274–312MPacm3/g.