Synthesis and characterization of copper gallium diselenide powders prepared from the sol–gel derived precursors

Copper gallium diselenide (CuGaSe₂) powders were synthesized via the sol–gel method followed by a selenization process. The sol–gel process can effectively reduce the required synthesis temperature to 400 °C due to enhanced reactivity and improved composition homogeneity. The amount of Cu₂Se impurity phase was decreased when sufficient Ga³⁺ was added to the precursors. CuGaSe₂ powders were successfully prepared when the Ga³⁺/Cu²⁺ molar ratio was increased to 2. The formation of CuGaSe₂ with a pure chalcopyrite structure was confirmed via the Rietveld refinement analysis. With decreasing Ga³⁺/Cu²⁺ molar ratios, the particle size of the prepared CuGaSe₂ powders was significantly enlarged because the copper selenide phase acted as a flux for the particle growth. The optical absorption spectra revealed the obtained CuGaSe₂ to have a band gap of 1.68 eV. The sol–gel method combined with the selenization process was demonstrated to provide a potential approach for fabricating CuGaSe₂ materials.     

CIGS absorbing layers prepared by RF magnetron sputtering from a single quaternary target

Cu(In_1−xGa_x)Se₂ (CIGS) thin films were prepared by RF magnetron sputtering from a single quaternary target at multiple processing parameters. The structural, compositional, and electrical properties of the as-deposited films were systematically investigated by XRD, Raman, SEM, and Hall effects analysis. The results demonstrate that by adjusting the processing parameters, the CIGS thin films with a preferential orientation along the (112) direction which exhibited single chalcopyrite phase were obtained. The films deposited at relatively higher substrate temperature, sputtering power, and Ar pressure exhibited favorable stoichiometric ratio (Cu/(In+Ga):0.8–0.9 and Ga/(In+Ga):0.25–0.36) with grain size of about 1–1.5 µm, and desirable electrical properties with p-type carrier concentration of 10¹⁶−10¹⁷ cm⁻³ and carrier mobility of 10–60 cm²/Vs. The CIGS layers are expected to fabricate high efficiency thin film solar cells.     

Cyclic voltammetry study of electrodeposition of Cu(In,Ga)Se2 thin films

The electrodeposition of Cu(In,Ga)Se₂ has been investigated by cyclic voltammetry (CV) in a DMF-aqueous solution that contained citrate as a complexing agent. The effects of the citrate ion on the reduction potentials of Cu²⁺, In³⁺, Ga³⁺ and H₂SeO₃ were examined for a unitary system. Furthermore, a cyclic voltammetry study was performed in a ternary Cu-In-Se system, a quaternary Cu-In-Ga-Se system, and binary Cu-Se, In-Se and Ga-Se systems. The insertion of In and Ga into the solid phase may proceed by an underpotential deposition mechanism, which involves two different routes: In³⁺ and Ga³⁺ reduction by a surface-induced effect from Cu₃Se₂ and/or reaction with H₂Se.     

Influence of inverse spinel structured CuGa2O4 on microwave dielectric properties of normal spinel ZnGa2O4 ceramics

Spinel Zn_1‐xCu_xGa₂O₄ (x = 0‐0.15) ceramics were prepared by the conventional solid‐state method. Only a single phase was indexed in all samples. The continuous lattice contraction of ZnGa₂O₄ unit cell was caused by Cu²⁺ substitution, and the lattice parameter shows a linear correlation with the content of Cu. The refined crystal structure parameters suggest that Cu²⁺ preferentially occupies the octahedron site, and the degree of inversion of Zn_1‐xCu_xGa₂O₄ (x = 0‐0.15) ceramics almost equals to the content of Cu²⁺. The relative intensity of A*_1g mode in Raman spectra confirm that the degree of inversion climbed with the growing content of Cu²⁺. The experimental and theoretical dielectric constant of Zn_1‐xCu_xGa₂O₄ ceramics fit well. Zn_1‐xCu_xGa₂O₄ (x = 0.01) ceramics sintered at 1400°C for 2 h exhibited good microwave dielectric properties, with ε_r = 9.88, Q × f = 131,445 GHz, tanδ = 6.85 × 10^?5, and τ_f = ?60 ppm/°C.     

Characterization of non-stoichiometric Ga2O3-x thin films grown by radio-frequency powder sputtering

We report the synthesis and characterization of non-stoichiometric Ga₂O_3-x thin films deposited on sapphire (0001) substrates by radio-frequency powder sputtering. The chemical and electronic states of the non-stoichiometric Ga₂O_3-x thin films were investigated. By sputtering in an Ar atmosphere, the as-grown thin films become non-stoichiometric Ga₂O_2.7, due to the difference in sputtering yield between Ga and O species of the Ga₂O₃ target. The electronic states of the thin films consist of ~85% Ga³⁺ and ~15% Ga¹⁺, corresponding to Ga₂O₃ and Ga₂O, respectively. The films have the electrical characteristics of a semiconductor, with electrical conductivity of approximately 5.0 × 10^-4 S cm^-1 and a carrier concentration of 4.5 × 10¹⁴ cm^-3 at 300 K.     

Nonvacuum Solution Synthesis of (Ag,Cu)(In,Ga)Se2 Absorbers for Applications in Thin‐Film Solar Cells

The effects of selenization temperatures on the phase formation and the photovoltaic properties of silver‐ion‐doped Cu(In,Ga)Se₂ (ACIGS) films were investigated. Cu_2?xSe phase coexisted with CuInSe₂ phase in the films as the selenization temperature was relatively low. Increasing the selenization temperatures promoted the formation of the chalcopyrite phase and increased the grain size. Upon increasing the selenization temperature to 600°C, single‐phased ACIGS films with a grain size of 2.1–2.2 μm were successfully synthesized. The incorporation of Ag⁺ and Ga³⁺ ions into CuInSe₂ during the phase formation of ACIGS elevated the band gaps of the films, thereby improving the open‐circuit voltage (V_oc) of the solar cells. The grain growth on raising the selenization temperatures also elevated the short‐circuit current (J_sc) values owing to the suppression of the electron‐hole recombination at grain boundaries. In the diode analysis, the facilitated phase formation suppressed the shunt path, decreasing the values of the diode factor (A), shunt conductance (G), and saturated current (J_o), thereby improving the cell performance. In this study, ACIGS solar cells with an efficiency of 7.21% prepared via the nonvacuum process were first demonstrated.     

Chemical solution deposition of epitaxial indium- and aluminum-doped Ga2O3 thin films on sapphire with tunable bandgaps

Compared to the vacuum-required deposition techniques, the chemical solution deposition (CSD) technique is superior in terms of low cost and ease of cation adjustment and upscaling. In this work, highly epitaxial indium- and aluminum-doped Ga₂O₃ thin films are deposited using a novel CSD technique. The 2θ, rocking curve, and φ-scan modes of x-ray diffraction (XRD) measurements and high-resolution transmission electron microscopy suggest that these thin films have a pure beta phase with good in- and out-of-plane crystallization qualities. The effect of incorporating indium and aluminum into the crystallization process is studied using high-temperature in situ XRD measurements. The results indicate that indium and aluminum doping can shift the crystallization of the thin films to lower and higher temperatures, respectively. Additionally, ultraviolet-visible spectroscopy measurements indicate that the bandgap of the sintered thin films can be tuned from 4.05 to 5.03 eV using a mixed precursor solution of In:Ga = 3:7 and Al:Ga = 3:7. The photodetectors based on the (InGa)₂O₃, pure Ga₂O₃, and (AlGa)₂O₃ samples exhibit the maximum photocurrents at 280, 255, and 230 nm, respectively. The results suggest that the described CSD technique is promising for producing high-quality bandgap tunable deep-ultraviolet photoelectrical and high-power devices.     

Preparation and Characterization of Silver‐Doped Cu(In,Ga)Se2 Films via Nonvacuum Solution Process

Cu(In,Ga)Se₂ films doped with different contents of silver ions (Ag⁺) were successfully prepared using nonvacuum spin coating followed by selenization at elevated temperatures. Increasing the Ag⁺ ion content increased the lattice parameters of the chalcopyrite structure, and shifted the A1 mode in the Raman signals to low frequencies. The band gaps of the prepared (Ag,Cu)(In,Ga)Se₂ (ACIGS) films were considerably increased, thereby increasing the open‐circuit voltage (V_oc) of the solar cells. As Ag⁺ ion content increased, the microstructures of ACIGS films became densified because the formed (Cu,Ag)₂In alloy phase with a low melting point facilitated liquid‐phase sintering. The evaporation of selenium species was correspondingly suppressed in the films during selenization, thereby reducing the selenium vacancies. The improvement in the microstructures and the defects of ACIGS films increased short‐circuit current (J_sc) and fill factor of the solar cells. The spectral response of the solar cells was also enhanced remarkably. This study demonstrated that incorporation of Ag⁺ ions into Cu(In,Ga)Se₂ films substantially improved the efficiency of the solar cells.     

New Magneto‐Optical Film of Ce,Ga:GIG with High Performance

Ce³⁺‐doped Gd₃Fe₅O₁₂ (Ce:GIG) film has a good application prospect in the field of integrated optical device. In this article, Ce:GIG and Ce,Ga:GIG films were deposited onto the quartz glass substrate by using radio‐frequency magnetron sputtering technology. The crystal phase, surface morphology, magnetization, and magnetic circular dichroism properties of films were characterized by using the X‐ray powder diffraction, atomic force microscopy, vibrating sample magnetometer, and circular dichroism spectrometer. The results show that as‐prepared Ce,Ga:GIG films has a good quality and show an excellent magneto‐optical performance, and the doping of Ga³⁺ ion and the annealing process have significant effect on the magnetism and magneto‐optical performances. It is expected that Ce,Ga:GIG film with a moderate Ga³⁺‐doping content is a better candidate than Ce:GIG and Ce:YIG films for the next generation of integrated optical isolator and other magneto‐optical equipment.     

A Promising Modified SILAR Sequence for the Synthesis of Photoelectrochemically Active Cu2ZnSnS4 (CZTS) Thin Films

A promising modified SILAR sequence approach has been employed for the synthesis of photoelectrochemically active Cu₂ZnSnS₄ (CZTS) thin films. To study the influence of sulfurization temperatures on the CZTS thin films, the CZTS precursor thin films were annealed at temperatures of 520, 540, 560, and 580 °C for 1 h in an H₂S (5 %)+Ar (95 %) atmosphere. These films were characterized for their structural, morphological, and optical properties using X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, and UV-vis spectrophotometer techniques. The film sulfurized at an optimized temperature of 580 °C shows the formation of a prominent CZTS phase with a dense microstructure and optical band gap energy of 1.38 eV. The photoelectrochemical (PEC) device fabricated using optimized CZTS thin films sulfurized at 580 °C exhibits an open circuit voltage (V_oc) of 0.38 V and a short circuit current density (J_sc) of 6.49 mA cm⁻², with a power conversion efficiency (η) of 0.96 %.     

Enhanced Thermoelectric Properties in Cu‐Doped c‐Axis‐Oriented Ca3Co4O9+δ Thin Films

Highly c‐axis‐oriented Ca₃Co_4?xCu_xO_9+δ (x = 0, 0.1, 0.2, and 0.3) thin films were prepared by chemical solution deposition on LaAlO₃ (001) single‐crystal substrates. X‐ray diffraction, field‐emission scanning electronic microscopy, X‐ray photoelectron spectroscopy, and ultraviolet‐visible absorption spectrums were used to characterize the derived thin films. The solubility limit of Cu was found to be less than 0.2, above which [Ca₂(Co_0.65Cu_0.35)₂O₄]_0.624CoO₂ with quadruplicated rock‐salt layers was observed. The electrical resistivity decreased monotonously with increasing Cu‐doping content when x ≤ 0.2, and then slightly increased with further Cu doping. The Seebeck coefficient was enhanced from ~100 μV/K for the undoped thin film to ~120 μV/K for the Cu‐doped thin films. The power factor was enhanced for about two times at room temperature by Cu doping, suggesting that Cu‐doped Ca₃Co₄O_9+δ thin films could be a promising candidate for thermoelectric applications.     

Greatly improved NIR shielding performance of CuS nanocrystals by gallium doping for energy efficient window

In this work, gallium doped copper sulfide (Ga-doped CuS) nanocrystals were prepared using a solvothermal method. The effects of Ga doping on the crystal structures, chemical composition, morphology, optical properties and thermal performance of copper sulfide (CuS) were investigated. The Ga-doped CuS nanocrystals had a hexagonal structure comparable to that of pure CuS. The Cu⁺/Cu²⁺ ratio first decreased and then increased with increasing Ga³⁺ doping. Both CuS and Ga-doped CuS exhibited nanoplate and nanorod morphologies. The visible transmittance of the Ga-doped CuS films was in the range of 61–77.1%. Importantly, the near-infrared (NIR) shielding performance of the films can be tuned by adjusting the concentration of the Ga dopant. The NIR shielding value of the optimal Ga-doped CuS film was 72.4%, which was approximately 1.5 times as high as that of the pure CuS film. This can be ascribed to the enhanced plasmonic NIR absorption that resulted from an increase in the hole concentration after doping with Ga³⁺ ions. In the thermal performance test, the Ga-doped CuS film lowered the interior temperature of the heat box by 9.1 °C. Therefore, the integration of good visible transmittance and high NIR shielding performance make the Ga-doped CuS nanocrystals a promising candidate for energy-efficient window coatings.     

Growth and properties of Cu3SbS4 thin films prepared by a two-stage process for solar cell applications

Cu₃SbS₄ is a promising material for thin film heterojunction solar cells owing to its suitable optical and electrical properties. In this paper, we report the preparation of Cu₃SbS₄ thin films by annealing the Sb₂S₃/CuS stacks, produced by chemical bath deposition, in a graphite box held at different temperatures. The influence of annealing temperature on the growth and properties of these films is investigated. These films are systematically analyzed by evaluating their structural, microstructural, optical and electrical properties using suitable characterization techniques. X-ray diffraction analysis showed that these films exhibit tetragonal crystal structure with the lattice parameters a=0.537 nm and b=1.087 nm. Their crystallite size increases with increasing annealing temperature of the stacks. Raman spectroscopy analysis of these films exhibited modes at 132, 247, 273, 317, 344, 358 and 635 cm⁻¹ due to Cu₃SbS₄ phase. X-ray photoelectron spectroscopy analysis revealed that the films prepared by annealing the stack at 350 °C exhibit a Cu-poor and Sb-rich composition with +1, +5 and −2 oxidation states of Cu, Sb and S, respectively. Morphological studies showed an improvement in the grain size of the films on increasing the annealing temperature. The direct optical band gap of these films was in the range of 0.82–0.85 eV. Hall measurements showed that the films are p-type in nature and their electrical resistivity, hole mobility and hole concentration are in the ranges of 0.14–1.20 Ω-cm, 0.05–2.11 cm² V⁻¹ s⁻¹ and 9.4×10²⁰–1.4×10¹⁹ cm⁻³, respectively. These structural, morphological, optical and electrical properties suggest that Cu₃SbS₄ could be used as an absorber layer for bottom cell in multi-junction solar cells.     

Effect of periodic precursor on sulfurization process of Cu2ZnSnS4 thin film

In this study, Cu₂ZnSnS₄ (CZTS) thin films were fabricated by periodically sequential depositions of metallic precursors by magnetron sputtering followed by sulfurization. The element compositions, crystal structures, and surface morphologies of the single-period precursor (Zn/Sn/Cu) and four-period precursor (Zn/Sn/Cu/Zn/Sn/Cu/Zn/Sn/Cu/Zn/Sn/Cu) during the sulfurization process were investigated. The experimental results showed that in the initial stage of sulfurization, the single-period precursor had a more efficient reaction with sulfur vapor below 300?°C because of its thicker metal layers. During the process of sulfurization, the CZTS phase first formed in the four-period film at 400?°C, owing to the wide distribution of the internal layer in the periodic thin film. With a further increase in temperature, the crystallinity of CZTS was enhanced and the secondary phases were reduced. A CZTS phase with Cu-poor and Zn-rich composition was confirmed in both thin films after complete sulfurization. The CZTS thin film with a four-period precursor showed a better degree of crystallization, and a single phase of CZTS was obtained more easily than in the single-period thin film. Therefore, using a periodic structure can promote the sulfurization reaction of Cu-Zn-Sn precursors and enhance the properties of CZTS thin films.     

Low-temperature sintering of highly conductive ZnO:Ga:Cl ceramics by means of chemical vapor transport

A new technology for sintering a ZnO + Ga₂O₃ powder via chemical vapor transport based on HCl has been developed. The proposed sintering method has the following advantages: a low sintering temperature of 1000–1100 °C, there is no need to use of expensive dopant nanopowders, the possibility of multiple re-sintering, and the absence of changes in the diameter of the ceramics after sintering. A ZnO:Ga:Cl ceramics with a density of 5.31 g/cm³, a hardness of 2.0 GPa, and a resistivity of 1.46 × 10^–3 Ω?cm has been synthesized. The solubility limit of the Ga₂O₃ dopant has been estimated at about 3 mol %. At a higher doping level, the content of the ZnGa₂O₄ spinel phase becomes significant. In addition, ZnO:Ga:Cl thin films with a resistivity of 2.77 × 10^–4 Ω?cm can be grown by DC magnetron sputtering of the synthesized ceramics.     

Structural,magnetic and electrical properties of Ga-substituted NiCuZn nanocrystalline ferrite

In this work, we studied the substitution effect of iron by gallium on the structural, magnetic and electrical properties of the ferrite system; Ni_0.5Cu_0.25Zn_0.25Fe_2−xGa_xO₄ (x = 0–1.0), synthesized by using the urea combustion method. XRD patterns of the samples calcined at 700 °C show only cubic spinel ferrite with an average crystallite sizes in the range of 40–54 nm. The lattice parameters were slightly changed with increasing Ga content which can be explained on the basis of the relative ionic radii of Ga³⁺ and Fe³⁺ ions. FT-IR measurements show two fundamental absorption bands, assigned to the vibration of tetrahedral and octahedral complexes, which were slightly changed with increasing Ga content. Mössbauer measurements enable us to predict the possible cation distribution of the system. It was found that Ga³⁺ ion prefer to substitute Fe³⁺ ions located in the octahedral site. Superparamagnetic state was observed in the Mössbauer spectra of the samples with Ga content >0.5. The decrease of the magnetic hyperfine field with gallium concentration was explained on the basis of supertransferred hyperfine interaction. A semiconducting behavior was inferred for all samples and the conductivity values were found to decrease with increasing the Ga content. The conduction mechanism in the spinel ferrite compounds was explained in terms of the hopping conduction process. The dielectric constant measured as a function of frequency and temperature was found to be dependent on the Ga concentration. The determined transition temperature was found to decrease with increasing Ga content.     

Solution-based synthesis of dense,large grained CuIn(S,Se)2 thin films using elemental precursor

Compared with the expensive and complicated vacuum techniques, the solution-based process to deposit I-III-VI₂ chalcogenide thin films (I=Cu, III=In or Ga, VI=S or Se) has attracted great interests due to its lower cost, higher scalable production and better application in flexible substrate. Herein, a low-toxic and high-active mixture solvent comprised of 1, 2-ethanedithiol and 1,2-ethylenediamine is utilized to dissolve elemental Cu, In and S powders at 60 °C, forming the CuInS₂ (CIS) precursor solution. After spin coating and annealing in a both Ar gas and selenium atmosphere, a dense and large-grained chalcopyrite CuIn(S,Se)₂ (CISSe) thin films with a close-packed grain size of ~800 nm are prepared, eliminating a undesired fine fine-grained bottom layer. In addition, the selenization temperature of the CISSe thin films is also discussed, which influences the phase composition, crystallinity and morphology of CISSe thin films. Photovoltaic device of the CISSe-based thin films is fabricated, obtaining a power conversion efficiency of 6.2% with an active cell area of 0.5 cm² under AM 1.5 illumination.     

In situ Ga K edge XANES study of the activation of Ga/ZSM-5 prepared by chemical vapor deposition of trimethylgallium

The activation of a dimethylgallium/ZSM-5 precursor to well-defined reduced and oxidized species is studied by in situ Ga K edge XANES. The precursor is prepared by chemical implanting of trimethylgallium on acidic HZSM-5. Subsequent reduction leads to charge-compensating Ga⁺ species. Direct oxidation of the trimethylgallium precursor leads to various forms of gallium oxide and regeneration of Brønsted acid protons. Oxidation of the reduced Ga⁺ species yields predominantly to GaO⁺ species. The GaO⁺ species exhibit a much higher H₂/D₂ exchange activity than reduced Ga⁺ species.     

How is 68Ga Labeling of Macrocyclic Chelators Influenced by Metal Ion Contaminants in 68Ge/68Ga Generator Eluates?

To assess the influence of Zn²⁺, Cu²⁺, Fe³⁺, Al³⁺, Ti^IV, and Sn^IV on incorporation of ⁶⁸Ga³⁺ into pendant‐arm macrocyclic chelators, the ⁶⁸Ga labeling of 1,4,7‐triazacyclononane‐1,4,7‐triacetic acid (NOTA), 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid (DOTA), 1,4,7‐triazacyclononane‐1,4,7‐tris[methyl(2‐carboxyethyl)phosphinic acid]) (TRAP), and 1,4,7‐triazacyclononane‐1‐[methyl(2‐carboxyethyl)phosphinic acid]‐4,7‐bis[methyl(2‐hydroxymethyl)phosphinic acid] (NOPO), as well as their peptide conjugates, was investigated in the presence of varying concentrations of these metal ions. The ⁶⁸Ga labeling yield for carboxylate‐type chelators NOTA and DOTA is decreased at lower metal ion contaminant concentrations compared with phosphinate‐type chelators TRAP and NOPO. The latter are able to rapidly exchange coordinated Zn^II with ⁶⁸Ga³⁺, as confirmed by mass spectrometry and ³¹P NMR spectroscopy. ⁶⁸Ga labeling of Zn^II complexes of TRAP and NOPO proceeds as efficient as labeling of neat NOTA; this applies also to the corresponding peptide conjugates of these chelators. This behavior results in substantially improved selectivity for Ga³⁺ and, therefore, in more robust and reliable ⁶⁸Ga labeling procedures. In addition, none of the investigated chelators binds ⁶⁸Ge, rendering post‐labeling purification protocols, for example, solid‐phase extraction, a reliable means of removal of ⁶⁸Ge contamination from ⁶⁸Ga radiopharmaceuticals.     

Physicochemical properties and catalytic performance of galloaluminosilicate in aromatization of lower alkanes: a comparative study with Ga/HZSM-5

A series of gallium-containing HZSM-5 zeolites with different Ga contents (Ga/(Al+Ga)?=?0.1?C0.6) were prepared by hydrothermal in situ synthesis and post synthesis. Their catalytic performance were compared in the aromatization of propane, butane and propane/butane mixture (1:1?molar). Galloaluminosilicate obtained via hydrothermal in situ synthesis exhibited high fraction of acidic framework Ga³⁺ with few dispersed extracrystalline Ga₂O₃. Ga/HZSM-5 obtained by post synthesis showed the presence of extracrystalline Ga₂O₃ and/or extra framework gallyl ions. The aromatization performance of Ga-containing HZSM-5 followed the following sequence; galloaluminosilicate > Ga/HZSM-5 (ion-exchange) > Ga/HZSM-5 (impregnation) ? HZSM-5. Optimum aromatization performance over galloaluminosilicate was achieved with Ga/(Al+Ga) ratio of 0.3. Propane conversion reached 50.9?wt% over galloaluminosilicate with Ga/(Al+Ga) of 0.3, as compared to 31.8 and 40.7?wt% for the corresponding Ga/HZSM-5 obtained by impregnation and ion-exchange, respectively, at gas hourly space velocity of 1,600?h^?1, and 540?°C. Comparison of aromatic selectivity at the same conversion level (~10.0?wt%) revealed that galloaluminosilicate is more selective than Ga/HZSM-5. The superior performance of galloaluminosilicate was attributed to the presence of highly dispersed-reducible extra-framework Ga₂O₃ (Lewis-dehydrogenating sites) formed by degalliation in close proximity to zeolitic Br?nsted sites. Thus, hydrothermal in situ approach can thus be considered as an effective method for improving the aromatization performance of HZSM-5.