Phosphine free synthesis of copper telluride nanocrystals in 1D and 2D shapes using Dipehylditelluride (DPDTe) as an air-stable source.

In this paper, we have developed a 'phosphine-free' method for synthesising copper telluride nanocrystals using diphenyl ditelluride as an air-stable tellurium source. The diphenyl ditelluride is shown to have optimal reactivity for the colloidal synthesis of Cu2Te, allowing optimal control over the phase and morphology. Using this unexplored Te precursor for copper telluride synthesis, 1D nanorods of hexagonal phase (Cu2Te) were synthesised at a moderate temperature of 180 °C. The precise control over key parameters for this system results in Cu2-xTe nanocrystals forming with varied shapes (1D nanorods and 2D nanoplates), sizes, and crystal phases (hexagonal Cu2Te and orthorhombic Cu1.43Te).

Thermoelectric Performance of Surface-Engineered Cu1.5-xTe-Cu2Se Nanocomposites.

Cu2-xS and Cu2-xSe have recently been reported as promising thermoelectric (TE) materials for medium-temperature applications. In contrast, Cu2-xTe, another member of the copper chalcogenide family, typically exhibits low Seebeck coefficients that limit its potential to achieve a superior thermoelectric figure of merit, zT, particularly in the low-temperature range where this material could be effective. To address this, we investigated the TE performance of Cu1.5-xTe-Cu2Se nanocomposites by consolidating surface-engineered Cu1.5Te nanocrystals. This surface engineering strategy allows for precise adjustment of Cu/Te ratios and results in a reversible phase transition at around 600 K in Cu1.5-xTe-Cu2Se nanocomposites, as systematically confirmed by in situ high-temperature X-ray diffraction combined with differential scanning calorimetry analysis. The phase transition leads to a conversion from metallic-like to semiconducting-like TE properties. Additionally, a layer of Cu2Se generated around Cu1.5-xTe nanoparticles effectively inhibits Cu1.5-xTe grain growth, minimizing thermal conductivity and decreasing hole concentration. These properties indicate that copper telluride based compounds have a promising thermoelectric potential, translated into a high dimensionless zT of 1.3 at 560 K.

Bottom-Up Synthesis of SnTe-Based Thermoelectric Composites.

There is a need for the development of lead-free thermoelectric materials for medium-/high-temperature applications. Here, we report a thiol-free tin telluride (SnTe) precursor that can be thermally decomposed to produce SnTe crystals with sizes ranging from tens to several hundreds of nanometers. We further engineer SnTe-Cu2SnTe3 nanocomposites with a homogeneous phase distribution by decomposing the liquid SnTe precursor containing a dispersion of Cu1.5Te colloidal nanoparticles. The presence of Cu within the SnTe and the segregated semimetallic Cu2SnTe3 phase effectively improves the electrical conductivity of SnTe while simultaneously reducing the lattice thermal conductivity without compromising the Seebeck coefficient. Overall, power factors up to 3.63 mW m-1 K-2 and thermoelectric figures of merit up to 1.04 are obtained at 823 K, which represent a 167% enhancement compared with pristine SnTe.

Novel Nanoarchitectured Cu2Te as a Photocathodes for Photoelectrochemical Water Splitting Applications.

Designing photocathodes with nanostructures has been considered a promising way to improve the photoelectrochemical (PEC) water splitting activity. Cu2Te is one of the promising semiconducting materials for photoelectrochemical water splitting, the performance of Cu2Te photocathodes remains poor. In this work, we report the preparation of Cu2Te nanorods (NRs) and vertical nanosheets (NSs) assembled film on Cu foil through a vapor phase epitaxy (VPE) technique. The obtained nano architectures as photocathodes toward photoelectrochemical (PEC) performance was tested afterwards for the first time. Optimized Cu2Te NRs and NSs photocathodes showed significant photocurrent density up to 0.53 mA cm-2 and excellent stability under illumination. Electrochemical impedance spectroscopy and Mott-Schottky analysis were used to analyze in more detail the performance of Cu2Te NRs and NSs photocathodes. From these analyses, we propose that Cu2Te NRs and NSs photocathodes are potential candidate materials for use in solar water splitting.

Synthesis of Copper Telluride Thin Films by Electrodeposition and Their Electrical and Thermoelectric Properties.

Intermetallic copper telluride thin films, which are important in a number of electronics fields, were electrodeposited using a potentiostatic method in low-pH aqueous electrolyte baths with various ion-source concentrations, and the electrical properties of the formed films were investigated after exfoliation from the substrate. The films were electrochemically analyzed by cyclic voltammetry, while surface and cross-sectional morphologies, compositional ratios, and electrical properties were analyzed by scanning electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and Hall-effect experiments. The copper telluride thin films, which were synthesized at various potentials in each bath, exhibit different composition ratios and structures; consequently, they show a variety of electrical and thermoelectric properties, including different electrical conductivities, carrier concentrations, mobilities, and Seebeck coefficients. Among them, the thin film with a 1:1 Cu:Te ratio delivered the highest power factor due to carrier filtering at the interface between the two phases.

Structural Modularization of Cu2 Te Leading to High Thermoelectric Performance near the Mott-Ioffe-Regel Limit.

To date, thermoelectric materials research stays focused on optimizing the material's band edge details and disfavors low mobility. Here, the paradigm is shifted from the band edge to the mobility edge, exploring high thermoelectricity near the border of band conduction and hopping. Through coalloying iodine and sulfur, the plain crystal structure is modularized of liquid-like thermoelectric material Cu2 Te with mosaic nanograins and the highly size mismatched S/Te sublattice that chemically quenches the Cu sublattice and drives the electronic states from itinerant to localized. A state-of-the-art figure of merit of 1.4 is obtained at 850 K for Cu2 (S0.4 I0.1 Te0.5 ); and remarkably, it is achieved near the Mott-Ioffe-Regel limit unlike mainstream thermoelectric materials that are band conductors. Broadly, pairing structural modularization with the high performance near the Mott-Ioffe-Regel limit paves an important new path towards the rational design of high-performance thermoelectric materials.

Preparation and Characterization of Te/Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate)/Cu7Te4 Ternary Composite Films for Flexible Thermoelectric Power Generator.

In this work, Te/poly(3,4-ethylenedioxythiophene) (PEDOT):poly(styrenesulfonate) (PSS)/Cu7Te4 ternary thermoelectric (TE) nanocomposite films were successfully fabricated by physical mixing and then drop casting. An optimum power factor of 65.3 µW/mK2 was acquired from a composite film containing 95 wt % PEDOT:PSS-coated Te (PC/Te) nanorods at 300 K, which was about 5 times as large as that of the PC/Cu7Te4 nanorod film and about 3 times as large as that of the PC/Te nanorod film. The power factor reached 112.3 µW/mK2 when the temperature was 380 K. Scanning transmission electron microscopy (STEM) and high-resolution STEM were used to observe the detailed internal microstructure of the composite film, revealing that the Te nanorods were single crystalline and the Cu7Te4 rods polycrystalline. The composite film was in fact a three-dimensional network interconnected with the PC/Te and PC/Cu7Te4 nanorods. The enhancement of the TE properties was ascribed to the synergetic effect of the two kinds of nanorods and the double-carrier filtering effect at the two heterointerfaces of Te/PEDOT:PSS and Cu7Te4/PEDOT:PSS. An eight single-leg flexible TE device consisting of the optimized composite film was fabricated, which produced a voltage of 31.2 mV and a maximum output power of 94.7 nW at a temperature gradient of 39 K.

Effective performance for undoped and boron-doped double-layered nanoparticles-copper telluride and manganese telluride on tungsten oxide photoelectrodes for solar cell devices.

This work demonstrates the synthesis of a novel double-layered Cu2-xTe/MnTe structure on a WO3 photoelectrode as a solar absorber for photovoltaic devices. Each material absorber is synthesized using a successive ionic layer adsorption and reaction (SILAR) method. The synthesized individual particle sizes are Cu2-xTe(17) ∼5-10nm and MnTe(3) ∼2nm, whereas, the aggregated particle sizes of undoped and boron-doped Cu2-xTe(17)/MnTe(11) are ∼50 and 150nm, respectively. The larger size after doping is due to the interconnecting of nanoparticles as a network-like structure. A new alignment of the energy band is constructed after boron/MnTe(11) is coated on boron/Cu2-xTe nanoparticles (NPs), leading to a narrower Eg equal to 0.58eV. Then, the valence band maximum (VBM) and conduction band minimum (CBM) with a trap state are also up-shifted to near the CBM of WO3, leading to the shift of a Fermi level for ease of electron injection. The best efficiency of 1.41% was yielded for the WO3/boron-doped [Cu2-xTe(17)/MnTe(11)] structure with a photocurrent density (Jsc)=16.43mA/cm(2), an open-circuit voltage (Voc)=0.305V and a fill factor (FF)=28.1%. This work demonstrates the feasibility of this double-layered structure with doping material as a solar absorber material.

Photovoltaic performances of Cu2-xTe sensitizer based on undoped and indium(3+)-doped TiO2 photoelectrodes and assembled counter electrodes.

Novel binary Cu2-xTe nanoparticles based on undoped and indium-doped TiO2 photoelectrodes were synthesized using a successive ionic layer adsorption and reaction (SILAR) technique as a sensitizer for liquid-junction solar cells. A larger diameter of TiO2 promoted a narrower energy band gap after indium doping, attributing to yield a broader absorption range of nanoparticle sensitizer due to the increasing amount of Cu2-xTe NPs on TiO2 surface. The atomic percentages showed the stoichiometric formation of Cu2Te incorporated in a Cu2-xTe structure. The best photovoltaic performance with the lower SILAR cycle, i.e., n=13 was performed after indium doping in both of carbon and Cu2S CEs and revealed that the efficiency of 0.73% under the radiant 100mW/cm(2) (AM 1.5G). The electrochemical impedance spectroscopy (EIS) was used to investigate the electrical properties via effect of material doping and counter electrodes with a lower charge-transfer resistance (Rct) and it was also found that the electron lifetime was improved after the sample doped with indium and assembled with carbon CE.