It is generally deemed that doping is a must for polymeric materials to achieve their high thermoelectric performance. We herein present the first report that intrinsically metallic behaviors and ...high-performance thermoelectric power factors can coexist within doping-free linear-backbone conducting polymers, poly(nickel-ethylenetetrathiolate) and its analogs. On the basis of density functional calculations, we have corroborated that four crystalline π-d conjugated transition-metal coordination polymers, including poly(Ni-C2S4), poly(Ni-C2Se4), poly(Pd-C2S4) and poly(Pt-C2S4) exhibit intrinsically metallic behavior arising from the formation of dense intermolecular interaction networks between sulfur/selenium atoms. They show moderate carrier concentrations (1019–1021 cm–3) and decent conductivities (103–104 S cm–1), among which, poly(Ni-C2S4), poly(Ni-C2Se4) and poly(Pd-C2S4) possess high power factors (∼103 μW m–1 K–2).
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IJS, KILJ, NUK, PNG, UL, UM
Abstract
The best known thermoelectric material for near room temperature heat-to-electricity conversion is bismuth telluride. Amongst the possible fabrication techniques, electrodeposition has ...attracted attention due to its simplicity and low cost. However, the measurement of the thermoelectric properties of electrodeposited films is challenging because of the conducting seed layer underneath the film. Here, we develop a method to directly measure the thermoelectric properties of electrodeposited bismuth telluride thin films, grown on indium tin oxide. Using this technique, the temperature dependent thermoelectric properties (Seebeck coefficient and electrical conductivity) of electrodeposited thin films have been measured down to 100 K. A parallel resistor model is employed to discern the signal of the film from the signal of the seed layer and the data are carefully analysed and contextualized with literature. Our analysis demonstrates that the thermoelectric properties of electrodeposited films can be accurately evaluated without inflicting any damage to the films.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
In this work, we present an automated platform for trapping and stretching individual micro- and nanoscale objects in solution using electrokinetic forces. The platform can trap objects at the ...stagnation point of a planar elongational electrokinetic field for long time scales, as demonstrated by the trapping of <100 nm polystyrene beads and DNA molecules for minutes, with a standard deviation in displacement from the trap center <1 μm. This capability enables the stretching of deformable nanoscale objects in a high-throughput fashion, as illustrated by the stretching of more than 400 DNA molecules within ∼4 hours. The flexibility of the electrokinetic stretcher opens up numerous possibilities for complex manipulation, with sequential stretching of a molecule at different voltages and multiple stretch-relaxation cycles of the same molecule as examples. The platform described provides an automated, high-throughput method to track and manipulate objects for real-time studies of micro- and nanoscale systems.
An automated microfluidic platform for trapping and stretching individual micro- and nanoscale objects in solution using electrokinetic forces.
The abrupt first-order metal–insulator phase transition in single-crystal vanadium dioxide nanowires (NWs) is engineered to be a gradual transition by axially grading the doping level of tungsten. We ...also demonstrate the potential of these NWs for thermal sensing and actuation applications. At room temperature, the graded-doped NWs show metal phase on the tips and insulator phase near the center of the NW, and the metal phase grows progressively toward the center when the temperature rises. As such, each individual NW acts as a microthermometer that can be simply read out with an optical microscope. The NW resistance decreases gradually with the temperature rise, eventually reaching 2 orders of magnitude drop, in stark contrast to the abrupt resistance change in undoped VO2 wires. This novel phase transition yields an extremely high temperature coefficient of resistivity ∼10%/K, simultaneously with a very low resistivity down to 0.001 Ω·cm, making these NWs promising infrared sensing materials for uncooled microbolometers. Lastly, they form bimorph thermal actuators that bend with an unusually high curvature, ∼900 m–1·K–1 over a wide temperature range (35–80 °C), significantly broadening the response temperature range of previous VO2 bimorph actuators. Given that the phase transition responds to a diverse range of stimuliheat, electric current, strain, focused light, and electric fieldthe graded-doped NWs may find wide applications in thermo-opto-electro-mechanical sensing and energy conversion.
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Copper antimony sulfides are regarded as promising catalysts for photo‐electrochemical water splitting because of their earth abundance and broad light absorption. The unique photoactivity of copper ...antimony sulfides is dependent on their various crystalline structures and atomic compositions. Here, a closed‐loop workflow is built, which explores Cu–Sb–S compositional space to optimize its photo‐electrocatalytic hydrogen evolution from water, by integrating a high‐throughput robotic platform, characterization techniques, and machine learning (ML) optimization workflow. The multi‐objective optimization model discovers optimum experimental conditions after only nine cycles of integrated experiments–machine learning loop. Photocurrent testing at 0 V versus reversible hydrogen electrode (RHE) confirms the expected correlation between the materials’ properties and photocurrent. An optimum photocurrent of −186 µA cm−2 is observed on Cu–Sb–S in the ratio of 9:45:46 in the form of single‐layer coating on F‐doped SnO2 (FTO) glass with a corresponding bandgap of 1.85 eV and 63.2% Cu1+/Cu species content. The targeted intelligent search reveals a nonobvious CuSbS composition that exhibits 2.3 times greater activity than baseline results from random sampling.
A closed‐loop workflow combining synthesis, deposition, characterization is used to explore Cu–Sb–S oxide films for efficient water reduction. The workflow narrows down optimal conditions for high photo‐electrocatalytic activity by optimizing for proxy objectives, including bandgap, Cu1+/Cu ratio, and film uniformity. This results in the successful identification of an optimal material composition through multi‐objective constrained optimization techniques.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Effective mass has been touted as an important descriptor in thermoelectric transport. Based on theoretical intuition, some reports demonstrate that low effective mass is preferable in ...thermoelectrics, while others propose that a large density of states effective mass for high Seebeck is the pathway to better thermoelectric materials. Leveraging on the available data from Materials Project, we present a data-driven conclusion that corroborates the central role of effective mass in high-throughput thermoelectric materials screening. The efficacy of the Fermi surface complexity factor in enhancing power factor is analyzed in relation to the effective mass for a large number of compounds. Here, we show that starting with a low inertial effective mass material, any changes in Fermi surface complexity factor will have a pronounced effect on its thermoelectric power factor and verify this strategy in recently discovered thermoelectric materials. This can be accomplished by employing band engineering using doping, or symmetry distortion, and starting with a base material that intrinsically possesses a low inertial effective mass.
The strongly correlated thermoelectric properties have been a major hurdle for high-performance thermoelectric energy conversion. One possible approach to avoid such correlation is to suppress phonon ...transport by scattering at the surface of confined nanowire structures. However, phonon characteristic lengths are broad in crystalline solids, which makes nanowires insufficient to fully suppress heat transport. Here, we employed Si–Ge alloy as well as nanowire structures to maximize the depletion of heat-carrying phonons. This results in a thermal conductivity as low as ∼1.2 W/m-K at 450 K, showing a large thermoelectric figure-of-merit (ZT) of ∼0.46 compared with those of SiGe bulks and even ZT over 2 at 800 K theoretically. All thermoelectric properties were “simultaneously” measured from the same nanowires to facilitate accurate ZT measurements. The surface-boundary scattering is prominent when the nanowire diameter is over ∼100 nm, whereas alloying plays a more important role in suppressing phonon transport for smaller ones.
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Phosphide-based thermoelectrics are a relatively less studied class of compounds, primarily due to the presence of light elements, which result in high thermal conductivity and inherent stability ...problems. In this work, we present a stable phosphide–tetrahedrite, Ag6Ge10P12, which possesses the highest zT (∼0.7) among all known phosphides at intermediate temperatures (750 K). We examine the intrinsic electronic and thermal transport properties of this compound by expressing the transport properties in terms of weighted mobility (μW), transport coefficient (σE0 ), and material quality factor (B), from which we are able to elucidate that the origin of its high zT can be attributed to the platelike Fermi surface and high level of band multiplicity related to its complex band structure. Finally, we discuss the origin of the low lattice thermal conductivity observed in this compound using experimental sound velocity, elastic properties, and Debye–Callaway model, thus laying the foundation for similar stable phosphides as potentially earth-abundant and nontoxic intermediate-temperature thermoelectric materials.
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IJS, KILJ, NUK, PNG, UL, UM
A new strategy of tuning the scattering mechanism to decouple electric conductivity with Seebeck coefficient for high‐performance thermoelectrics is realized by Jing Wu, Junpeng Lu, Zhenhua Ni, and ...co‐workers, as described in article number 2004786. By applying a gate voltage on a 2D Bi2O2Se‐based field‐effect transistor, a high thermoelectric power factor over a wide temperature range is achieved due to persistently high mobility arising from the highly gate‐tunable scattering mechanism.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A computationally efficient first-principles approach to predict intrinsic semiconductor charge transport properties is proposed. By using a generalized Eliashberg function for short-range ...electron–phonon scattering and analytical expressions for long-range electron–phonon and electron–impurity scattering, fast and reliable prediction of carrier mobility and electronic thermoelectric properties is realized without empirical parameters. This method, which is christened “Energy-dependent Phonon- and Impurity-limited Carrier Scattering Time AppRoximation (EPIC STAR)” approach, is validated by comparing with experimental measurements and other theoretical approaches for several representative semiconductors, from which quantitative agreement for both polar and non-polar, isotropic and anisotropic materials is achieved. The efficiency and robustness of this approach facilitate automated and unsupervised predictions, allowing high-throughput screening and materials discovery of semiconductor materials for conducting, thermoelectric, and other electronic applications.
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