Scalable synthesis of Cu-Sb-S phases from reactive melts of metal xanthates and effect of cationic manipulation on structural and optical properties

Thermoelectric Performance of Tetrahedrite (Cu12Sb4S13) Thin Films: The Influence of the Substrate and Interlayer

In the present work, tetrahedrite Cu12Sb4S13 thin films were deposited on various substrates via aerosol-assisted chemical vapor deposition (AACVD) using diethyldithiocarbamate complexes as precursors. A buffer layer of Sb2O3 with a small lattice mismatch to Cu12Sb4S13 was applied to one of the glass substrates to improve the quality of the deposited thin film. The buffer layer increased the coverage of the Cu12Sb4S13 thin film, resulting in improved electrical transport properties. The growth of the Cu12Sb4S13 thin films on the other substrates, including ITO-coated glass, a SiO2-coated Si wafer, and mica, was also investigated. Compared to the films grown on the other substrates, the Cu12Sb4S13 thin film deposited on the SiO2-coated Si wafer showed a dense and compact microstructure and a larger grain size (qualities that are beneficial for carrier transport), yielding a champion power factor (PF) of ∼362 μW cm-1 K-2 at 625 K. The choice of substrate strongly influenced the composition, microstructure, and electrical transport properties of the deposited Cu12Sb4S13 thin film. At 460 K, the highest zT value that was obtained for the thin films was ∼0.18. This is comparable to values reported for Cu-Sb-S bulk materials at the same temperature. Cu12Sb4S13 thin films deposited using AACVD are promising for thermoelectric applications. To the best of our knowledge, the first full thermoelectric characterization of the Cu12Sb4S13 thin film is performed in this work.

Multinary Tetrahedrite (Cu12-x-yMxNySb4S13) Nanoparticles: Tailoring Thermal and Optical Properties with Copper-Site Dopants

Tetrahedrite (Cu12Sb4S13) is an earth-abundant and nontoxic compound with prospective applications in green energy technologies such as thermoelectric waste heat recycling or photovoltaic power generation. A facile, one-pot solution-phase modified polyol method has been developed that produces high-purity nanoscale tetrahedrite products with exceptional stoichiometric and phase control. This modified polyol method is used here to produce phase-pure quaternary and quintenary tetrahedrite nanoparticles doped on the Cu-site with Zn, Fe, Ni, Mn, or Co. This is the first time that Cu-site codoped quintenary tetrahedrite and Mn-doped quaternary tetrahedrite have been produced by a solution-phase method. X-ray diffraction shows phase-pure tetrahedrite, while scanning and transmission electron microscopy show the size and morphology of the nanomaterials. Energy dispersive X-ray spectroscopy confirms nanoparticles have near-stoichiometric elemental compositions. Thermal stability of quintenary codoped tetrahedrite material is analyzed using thermogravimetric analysis, finding that codoping with Mn, Fe, Ni, and Zn increased thermal stability while codoping with cobalt decreased thermal stability. This is the first systematic study of the optical properties of quaternary and quintenary tetrahedrite nanoparticles doped on the Cu-site. Visible-NIR diffuse reflectance spectroscopy reveals that the quaternary and quintenary tetrahedrite nanoparticles have direct optical band gaps ranging from 1.88 to 2.04 eV. Data from thermal and optical characterization support that codoped tetrahedrite nanoparticles are composed of quintenary grains. This research seeks to enhance understanding of the material properties of tetrahedrite, leading to the optimization of sustainable, nontoxic, and high-performance photovoltaic and thermoelectric materials.

Molecular Precursor Routes for Ag-Based Metallic, Intermetallic, and Metal Sulfide Nanoparticles: Their Comparative ORR Activity Trend at Solid|Liquid and Liquid|Liquid Interfaces

The electrochemical conversion of oxygen to water is a crucial process required for renewable energy production, whereas its first two-electron step produces a versatile chemical and oxidant─hydrogen peroxide. Improving performance and widening the limited selection of the potential catalysts for this reaction is a step toward the implementation of clean-energy technologies. As silver is known as one of the most effective catalysts of oxygen reduction reaction (ORR), we have designed a suitable molecular precursor pathway for the selective synthesis of metallic (Ag), intermetallic (Ag₃Sb), and binary or ternary metal sulfide (Ag₂S and AgSbS₂) nanomaterials by judicious control of reaction conditions. The decomposition of xanthate precursors under different reaction conditions in colloidal synthesis indicates that carbon-sulfur bond cleavage yields the respective metal sulfide nanomaterials. This is not the case in the presence of trioctylphosphine when the metal-sulfur bond is broken. The synthesized nanomaterials were applied as catalysts of oxygen reduction at the liquid-liquid and solid-liquid interfaces. Ag exhibits the best performance for electrochemical oxygen reduction, whereas the electrocatalytic performance of Ag and Ag₃Sb is comparable for peroxide reduction in an alkaline medium. Scanning electrochemical microscopy (SECM) analysis indicates that a flexible 2-electron to 4-electron ORR pathway has been achieved by transforming metallic Ag into intermetallic Ag₃Sb.

Precursor-Mediated Colloidal Synthesis of Compositionally Tunable Cu-Sb-M-S (M = Zn, Co, and Ni) Nanocrystals and Their Transport Properties

The solution-based colloidal synthesis of multinary semiconductor compositions has allowed the design of new inorganic materials impacting a large variety of applications. Yet there are certain compositions that have remained elusive-particularly quaternary structures of transition metal-based (e.g., Co, Zn, Ni, Fe, Mn, and Cr) copper antimony chalcogenides. These are widely sought for tuning the electrical and thermal conductivity as a function of the size, composition, and crystal phase. In this work, a facile hot injection approach for the synthesis of three different tetrahedrite-substituted nanocrystals (NCs) (Cu₁₀Zn₂Sb₄S₁₃, Cu₁₀Co₂Sb₄S₁₃, and Cu₁₀Ni_1.5Sb₄S₁₃) and their growth mechanisms are investigated. We reveal that the interplay between the Zn, Ni, and Co precursors on the basis of thiophilicity is key to obtaining pure phase NCs with controlled size and shape. While all of the synthesized crystal phases display outstanding low thermal conductivity, the Cu_10.5Sb₄Ni_1.5S₁₃ system shows the most enhanced electrical conductivity compared to Cu₁₀Zn₂Sb₄S₁₃ and Cu₁₀Co₂Sb₄S₁₃. This study highlights an effective synthesis strategy for the growth of complex quaternary nanocrystals and their high potential for application in thermoelectrics.

Molecular precursor-mediated facile synthesis of photo-responsive stibnite Sb2S3 nanorods and tetrahedrite Cu12Sb4S13 nanocrystals

Stibnite Sb₂S₃ and tetrahedrite Cu₁₂Sb₄S₁₃ nanostructures being economical, environmentally benign and having a high absorption coefficient are highly promising materials for energy conversion applications. However, producing these materials especially tetrahedrite in the phase pure form is a challenging task. In this report we present a structurally characterized single source molecular precursor [Sb(4,6-Me₂pymS)₃] for the facile synthesis of binary Sb₂S₃ as well as ternary Cu₁₂Sb₄S₁₃ in oleylamine (OAm) at a relatively lower temperature. The as-prepared Sb₂S₃ and Cu₁₂Sb₄S₁₃ nanostructures were thoroughly checked for their phase purity, elemental composition and morphology by powder X-ray diffraction (pXRD), electron dispersive spectroscopy (EDS) and electron microscopy techniques. pXRD and EDS studies confirm the formation of phase pure, crystalline orthorhombic Sb₂S₃ and cubic Cu₁₂Sb₄S₁₃. The SEM, TEM and HRTEM images depict the formation of well-defined nanorods and nearly spherical nanocrystals for Sb₂S₃ and Cu₁₂Sb₄S₁₃, respectively. The Sb₂S₃ nanorods and Cu₁₂Sb₄S₁₃ nanocrystals exhibit an optical bandgap of ∼1.88 and 2.07 eV, respectively, which are slightly blue-shifted relative to their bulk bandgap, indicating the quantum confinement effect. Finally, efficient photoresponsivity and good photo-stability were achieved in the as-prepared Sb₂S₃ and Cu₁₂Sb₄S₁₃ nanostructure-based prototype photo-electrochemical cell, which make them promising candidates for alternative low-cost photon absorber materials.

Structural and Optical Characterization of Mechanochemically Synthesized CuSbS2 Compounds

One of the areas of research on materials for thin-film solar cells focuses on replacing In and Ga with more earth-abundant elements. In that respect, chalcostibite (CuSbS₂) is being considered as a promising environmentally friendly and cost-effective photovoltaic absorber material. In the present work, single CuSbS₂ phase was synthesized directly by a short-duration (2 h) mechanochemical-synthesis step starting from mixtures of elemental powders. X-ray diffraction analysis of the synthesized CuSbS₂ powders revealed a good agreement with the orthorhombic chalcostibite phase, space group Pnma, and a crystallite size of 26 nm. Particle-size characterization revealed a multimodal distribution with a median diameter ranging from of 2.93 μm to 3.10 μm. The thermal stability of the synthesized CuSbS₂ powders was evaluated by thermogravimetry and differential thermal analysis. No phase change was observed by heat-treating the mechanochemically synthesized powders at 350 °C for 24 h. By UV-VIS-NIR spectroscopy the optical band gap was determined to be 1.41 eV, suggesting that the mechanochemically synthesized CuSbS₂ can be considered suitable to be used as absorber materials. Overall, the results show that the mechanochemical process is a viable route for the synthesis of materials for photovoltaic applications.

Synthesis of ternary copper antimony sulfide via solventless thermolysis or aerosol assisted chemical vapour deposition using metal dithiocarbamates

Copper antimony sulfide (Cu-Sb-S) has recently been proposed as an attractive alternative photovoltaic material due to the earth-abundant and non-toxic nature of the elements, high absorption coefficients and band gaps commensurate with efficient harvesting of solar photonic flux across multiple phases of Cu-Sb-S. These materials are therefore highly desirable and sustainable and scalable deposition techniques to produce them are of interest. In this paper, we demonstrate two facile, low-temperature and inexpensive techniques (solventless thermolysis and aerosol-assisted chemical vapor deposition (AACVD)) for the preparation of binary digenite (Cu1.8S), chalcocite (Cu2S) and stibnite (Sb2S3) and several phases of ternary copper-antimony-sulfide (Cu2xSb2(1-x)Sy, where 0 ≤ x ≤ 1). It was found that by utilising these different techniques and varying the ratio of Cu:Sb, pure phases of ternary chalcostibite (CuSbS2), fematinite (Cu3SbS4) and tetrahedrite (Cu12Sb4S13) can be achieved. Two single-source precursors were investigated for this purpose, namely the diethyldithiocarbamate (DTC) complexes of copper and antimony Cu(DTC)2 and Sb(DTC)3. These were decomposed both individually (to produce binary materials) and combined (to produce ternary materials) at different ratios. From the solventless thermolysis and AACVD methods, either particulate or thin film material was formed, respectively. These materials were then characterised by powder XRD, SEM, EDX and Raman spectroscopies to determine the crystalline phase, material morphology and uniformity of elemental composition. This analysis demonstrated that as the Cu-content increases, the phase of the ternary material changes from chalcostibite (CuSbS2) and fematinite (Cu3SbS4) at a low Cu:Sb ratio to tetrahedrite (Cu12Sb4S13) at a high Cu:Sb ratio.

Gram-Scale Production of Photothermally Active Tetrahedrite Nanoparticles for Solar-Driven Water Evaporation

Pristine and substituted tetrahedrite nanoparticles have shown immense potential as low-cost and sustainable materials for energy conversion applications. However, the commonly used synthetic methods for their production are cumbersome and are not easily scalable. In this work, we report a facile colloidal synthetic protocol for the preparation of phase-pure samples of pristine (Cu₁₂ Sb₄ S₁₃ ) and Zn-substituted (Cu₁₁ ZnSb₄ S₁₃ ) tetrahedrite nanoparticles on the gram scale. Both tetrahedrite compositions were found to be photothermally responsive, enabling their use in solar-driven water evaporation.