Solution-based synthesis of wurtzite Cu2ZnSnS4 nanoleaves introduced by α-Cu2S nanocrystals as a catalyst

Design Principles of Colloidal Nanorod Heterostructures

Anisotropic heterostructures of colloidal nanocrystals embed size-, shape-, and composition-dependent electronic structure within variable three-dimensional morphology, enabling intricate design of solution-processable materials with high performance and programmable functionality. The key to designing and synthesizing such complex materials lies in understanding the fundamental thermodynamic and kinetic factors that govern nanocrystal growth. In this review, nanorod heterostructures, the simplest of anisotropic nanocrystal heterostructures, are discussed with respect to their growth mechanisms. The effects of crystal structure, surface faceting/energies, lattice strain, ligand sterics, precursor reactivity, and reaction temperature on the growth of nanorod heterostructures through heteroepitaxy and cation exchange reactions are explored with currently known examples. Understanding the role of various thermodynamic and kinetic parameters enables the controlled synthesis of complex nanorod heterostructures that can exhibit unique tailored properties. Selected application prospects arising from such capabilities are then discussed.

Copper Dithiocarbamates: Coordination Chemistry and Applications in Materials Science, Biosciences and Beyond

Copper dithiocarbamate complexes have been known for ca. 120 years and find relevance in biology and medicine, especially as anticancer agents and applications in materials science as a single-source precursor (SSPs) to nanoscale copper sulfides. Dithiocarbamates support Cu(I), Cu(II) and Cu(III) and show a rich and diverse coordination chemistry. Homoleptic [Cu(S2CNR2)2] are most common, being known for hundreds of substituents. All contain a Cu(II) centre, being either monomeric (distorted square planar) or dimeric (distorted trigonal bipyramidal) in the solid state, the latter being held together by intermolecular C···S interactions. Their d9 electronic configuration renders them paramagnetic and thus readily detected by electron paramagnetic resonance (EPR) spectroscopy. Reaction with a range of oxidants affords d8 Cu(III) complexes, [Cu(S2CNR2)2][X], in which copper remains in a square-planar geometry, but Cu–S bonds shorten by ca. 0.1 Å. These show a wide range of different structural motifs in the solid-state, varying with changes in anion and dithiocarbamate substituents. Cu(I) complexes, [Cu(S2CNR2)2]−, are (briefly) accessible in an electrochemical cell, and the only stable example is recently reported [Cu(S2CNH2)2][NH4]·H2O. Others readily lose a dithiocarbamate and the d10 centres can either be trapped with other coordinating ligands, especially phosphines, or form clusters with tetrahedral [Cu(μ3-S2CNR2)]4 being most common. Over the past decade, a wide range of Cu(I) dithiocarbamate clusters have been prepared and structurally characterised with nuclearities of 3–28, especially exciting being those with interstitial hydride and/or acetylide co-ligands. A range of mixed-valence Cu(I)–Cu(II) and Cu(II)–Cu(III) complexes are known, many of which show novel physical properties, and one Cu(I)–Cu(II)–Cu(III) species has been reported. Copper dithiocarbamates have been widely used as SSPs to nanoscale copper sulfides, allowing control over the phase, particle size and morphology of nanomaterials, and thus giving access to materials with tuneable physical properties. The identification of copper in a range of neurological diseases and the use of disulfiram as a drug for over 50 years makes understanding of the biological formation and action of [Cu(S2CNEt2)2] especially important. Furthermore, the finding that it and related Cu(II) dithiocarbamates are active anticancer agents has pushed them to the fore in studies of metal-based biomedicines.

Dithiocarbamate Complexes as Single Source Precursors to Nanoscale Binary, Ternary and Quaternary Metal Sulfides

Nanodimensional metal sulfides are a developing class of low-cost materials with potential applications in areas as wide-ranging as energy storage, electrocatalysis, and imaging. An attractive synthetic strategy, which allows careful control over stoichiometry, is the single source precursor (SSP) approach in which well-defined molecular species containing preformed metal-sulfur bonds are heated to decomposition, either in the vapor or solution phase, resulting in facile loss of organics and formation of nanodimensional metal sulfides. By careful control of the precursor, the decomposition environment and addition of surfactants, this approach affords a range of nanocrystalline materials from a library of precursors. Dithiocarbamates (DTCs) are monoanionic chelating ligands that have been known for over a century and find applications in agriculture, medicine, and materials science. They are easily prepared from nontoxic secondary and primary amines and form stable complexes with all elements. Since pioneering work in the late 1980s, the use of DTC complexes as SSPs to a wide range of binary, ternary, and multinary sulfides has been extensively documented. This review maps these developments, from the formation of thin films, often comprised of embedded nanocrystals, to quantum dots coated with organic ligands or shelled by other metal sulfides that show high photoluminescence quantum yields, and a range of other nanomaterials in which both the phase and morphology of the nanocrystals can be engineered, allowing fine-tuning of technologically important physical properties, thus opening up a myriad of potential applications.

A top-down strategy to synthesize wurtzite Cu2ZnSnS4 nanocrystals by green chemistry

Green synthesis of metastable wurtzite Cu2ZnSnS4 nanocrystals through a top-down synthetic strategy is presented. Formation mechanisms associated with Kirkendall and etching effects are illustrated in detail. The nanocrystals exhibit remarkable photoluminescence properties at room temperature.

Low-temperature synthesis of Cu2CoSnS4 nanoparticles by thermal decomposition of metal precursors and the study of its structural, optical and electrical properties for photovoltaic applications

Structural, opto-electrical properties of earth abundant quaternary chalcopyrite, Cu₂CoSnS₄ (CCTS) nanoparticles have been synthesized successfully by thermal decomposition process at a lower temperature with shorter processing time, are reported.

Wurtzite CZTS nanocrystals and phase evolution to kesterite thin film for solar energy harvesting

A quaternary indium- and gallium-free kesterite (KS)-based compound, copper zinc tin sulfide (Cu₂ZnSnS₄, CZTS), has received significant attention for its potential applications in low cost and sustainable solar cells.

Role of copper sulfide seeds in the growth process of CuInS2 nanorods and networks

CuInS2 nanorods and networks are interesting candidates for applications requiring efficient charge transport, such as solar energy conversion, because of the increased electrical conductivity in elongated or interconnected nanocrystals, compared to isolated, quasi-spherical ones. However, little is known about the growth mechanisms involved in the formation of this kind of nanostructures, yet. Here, CuInS2 nanorods and networks were synthesized through a facile low-cost and phosphine-free method. Copper and indium sources were added together in the presence of oleylamine and oleic acid. Changing the amount of oleic acid present in the reaction solution influenced the reactivity of the monomers, and consequently, the size of copper sulfide seeds formed in situ after the injection of tert-dodecanethiol, serving as the source of sulfur. Two different growth mechanisms of CuInS2 nanorods were observed, depending on the size of the copper sulfide seeds. Larger seeds (8 nm), which were generated with relatively small amounts of oleic acid, resulted in the formation of hybrid copper sulfide-copper indium disulfide nanocrystals as intermediates in the growth process of the nanorods, while smaller seeds (4 nm) obtained with relatively large amounts of oleic acid were gradually converted to copper indium sulfide nanorods. At longer reaction times, these nanorods formed network structures. The reaction between oleylamine and oleic acid at high temperature turned out to be the crucial factor to induce the attachment of nanorods to multipods and networks.

A nontoxic and low-cost hydrothermal route for synthesis of hierarchical Cu2ZnSnS4 particles

We explore a facile and nontoxic hydrothermal route for synthesis of a Cu2ZnSnS4 nanocrystalline material by using l-cysteine as the sulfur source and ethylenediaminetetraacetic acid (EDTA) as the complexing agent. The effects of the amount of EDTA, the mole ratio of the three metal ions, and the hydrothermal temperature and time on the phase composition of the obtained product have been systematically investigated. The addition of EDTA and an excessive dose of ZnCl2 in the hydrothermal reaction system favor the generation of kesterite Cu2ZnSnS4. Pure kesterite Cu2ZnSnS4 has been synthesized at 180°C for 12 h from the reaction system containing 2 mmol of EDTA at 2:2:1 of Cu/Zn/Sn. It is confirmed by Raman spectroscopy that those binary and ternary phases are absent in the kesterite Cu2ZnSnS4 product. The kesterite Cu2ZnSnS4 material synthesized by the hydrothermal process consists of flower-like particles with 250 to 400 nm in size. It is revealed that the flower-like particles are assembled from single-crystal Cu2ZnSnS4 nanoflakes with ca. 20 nm in size. The band gap of the Cu2ZnSnS4 nanocrystalline material is estimated to be 1.55 eV. The films fabricated from the hierarchical Cu2ZnSnS4 particles exhibit fast photocurrent responses under intermittent visible-light irradiation, implying that they show potentials for use in solar cells and photocatalysis.

Understanding the synthetic pathway of a single-phase quarternary semiconductor using surface-enhanced Raman scattering: a case of wurtzite Cu₂ZnSnS₄ nanoparticles

Single-phase Cu2ZnSnS4 (CZTS) is an essential prerequisite toward a high-efficiency thin-film solar cell device. Herein, the selective phase formation of single-phase CZTS nanoparticles by ligand control is reported. Surface-enhanced Raman scattering (SERS) spectroscopy is demonstrated for the first time as a characterization tool for nanoparticles to differentiate the mixed compositional phase (e.g., CZTS, CTS, and ZnS), which cannot be distinguished by X-ray diffraction. Due to the superior selectivity and sensitivity of SERS, the growth mechanism of CZTS nanoparticle formation by hot injection is revealed to involve three growth steps. First, it starts with nucleation of Cu(2-x)S nanoparticles, followed by diffusion of Sn(4+) into Cu(2-x)S nanoparticles to form the Cu3SnS4 (CTS) phase and diffusion of Zn(2+) into CTS nanoparticles to form the CZTS phase. In addition, it is revealed that single-phase CZTS nanoparticles can be obtained via balancing the rate of CTS phase formation and diffusion of Zn(2+) into the CTS phase. We demonstrate that this balance can be achieved by 1 mL of thiol with Cu(OAc)2, Sn(OAc)4, and Zn(acac)2 metal salts to synthesize the CZTS phase without the presence of a detectable binary/ternary phase with SERS.