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Mg3Sb2-based thermoelectric materials have recently received heightened attention due to their diverse merits of high band degeneracy, ultralow lattice thermal conductivity and high carrier mobility. However, the inherently low carrier concentration of pristine Mg3Sb2 seriously hinders the advancement of this material toward high thermoelectric performance. Therefore, searching for proper dopants to optimize the carrier concentration is one of the primary avenues to realize superior thermoelectric performance in Mg3Sb2-based materials. Herein, by considering the electronegativity difference Δχ and mass difference ΔM between the dopant and host elements, we theoretically and experimentally demonstrate lanthanide Gd as an effective dopant to tune the carrier concentration of Mg3Sb1.3Bi0.7 alloys. Owing to its high doping efficiency, a large carrier concentration up to 8.9 × 1019 cm−3 is realized through Gd doping, which is close to the optimal value. Moreover, the coarse grain size commendably mitigates the grain boundary effects and thus ensures high carrier mobility. Combining the greatly suppressed lattice thermal conductivity by point defect scattering, a maximum zT of 1.55 is achieved at 700 K in Mg3.065Sb1.3Bi0.7Gd0.015. [ABSTRACT FROM AUTHOR]

Coupling of a phase transition to electron and phonon transports provides extra degree of freedom to improve the thermoelectric performance, while the pertinent experimental and theoretical studies are still rare. Particularly, the impaction of chemical compositions and phase transition characters on the abnormal thermoelectric properties across phase transitions are largely unclear. Herein, by varying the Cu content x from 1.75 to 2.10, we systemically investigate the crystal structural evolution, phase transition features, and especially the thermoelectric properties during the phase transition for Cu x Se. It is found that the addition of over-stoichiometry Cu in Cu x Se could alter the phase transition characters and suppress the formation of Cu vacancies. The critical scatterings of phonons and electrons during phase transitions strongly enhance the Seebeck coefficient and diminish the thermal conductivity, leading to an ultrahigh dimensionless thermoelectric figure of merit of ∼1.38 at 397 K in Cu2.10Se. With the decreasing Cu content, the critical electron and phonon scattering behaviors are mitigated, and the corresponding thermoelectric performances are reduced. This work offers inspirations for understanding and tuning the thermoelectric transport properties during phase transitions. [ABSTRACT FROM AUTHOR]

Recently, a deformable and ductile inorganic semiconductor Ag2S has attracted intense attention due to its potential application in self-powered wearable and hetero-shaped electronics. However, the thermoelectric figure of merit (zT) of Ag2S is greatly limited by its extremely low carrier concentration. In this study, via doping I into Ag2S-based materials, we tune the carrier concentration into the optimal range as well as suppressing the lattice thermal conductivity. A maximum zT value of 0.26 is achieved for Ag2S0.7Se0.295I0.005 at 300 K, about three times higher than the matrix compound. More importantly, doping I has little effect on the ductility and deformability of Ag2S-based materials. Our study shows that I-doped Ag2S-based materials are good candidates for developing flexible thermoelectric technologies. [ABSTRACT FROM AUTHOR]

Cu2ZnSn(S,Se)4 are emerging as promising photovoltaic materials due to their outstanding photoelectrical performances, benign grain boundaries, and Earth‐abundant constituent elements. However, there are largely distributed cation‐disordering defects and defect clusters, which lead to an increase in recombination and a large open‐circuit voltage deficit and thus deteriorate device performance. Herein, defect control for a high‐efficiency Cu2ZnSn(S,Se)4 solar cell by atomic layer deposition of aluminum oxide (ALD‐Al2O3) on the precursor film is reporter. CuZn defects and Sn‐related deep defects are largely suppressed because of the decrease in Sn2+ and the increase in Sn4+ in the film by ALD‐Al2O3 on the precursor are found, and the crystallinity of absorber layer is improved from a double‐layer structure to a completely single‐layer structure. Furthermore, the carrier lifetime and recombination in the bulk and interface are significantly improved for devices with ultrathin Al2O3. Using this approach, the conversion efficiency increases from 8.8% to 11.0% and the open‐circuit voltage deficit decreases from 0.621 to 0.577 V. Herein, a deep understanding of the relationship between Al2O3 incorporation and high‐efficiency Cu2ZnSn(S,Se)4 devices and a new direction for controlling defects to further improve the performance of kesterite solar cells are provided. [ABSTRACT FROM AUTHOR]

Cu–Sn–S ternary compounds have attracted great attention in the thermoelectric community because they are composed of low-cost, earth-abundant, and non-toxic elements. Among them, Cu7Sn3S10 shows promising thermoelectric performance in the middle temperature range. In this work, through doping Br in Cu7Sn3S10, a peak dimensionless figure of merit (zT) around unity at 750 K has been achieved. Chemical composition analysis indicates that Br has a higher solubility in Cu7Sn3S10 than Cl. On one hand, the Br dopant introduces additional electrons and tunes the initial overhigh carrier concentration to the optimal range. On the other hand, the Br dopant creates strong strain field fluctuation to significantly suppress the lattice thermal conductivity to as low as 0.4 W m−1 K−1 at 750 K. Its synthetic effects advance the realization of high zT around unity in Br-doped Cu7Sn3S10. [ABSTRACT FROM AUTHOR]

Flexible electronics ushers in a revolution to the electronics industry in the 21st century. Ideally, all components of a flexible electronic device including the functional component shall comply with the deformation to ensure the structural and functional integrity, imposing a pressing need for developing room‐temperature strain‐tolerant semiconductors. To this end, there is a long‐standing material dilemma: inorganic semiconductors are typically brittle at room temperature except for size‐induced flexibility; by contrast, organic semiconductors are intrinsically soft and flexible but the electrical performance is poor. This is why the discovery of bulk plasticity in Ag2S at room temperature and ZnS in darkness is groundbreaking in solving this long‐standing material dilemma between the mechanical deformability and the electrical performance. The present review summarizes the background knowledge and latest advances in the emerging field of plastic inorganic semiconductors. At the outset, we argue that the plasticity of inorganic semiconductors is vital to strain tolerance of electronic devices, which has not been adequately emphasized. The mechanisms of plasticity are illustrated from the perspective of chemical bonding and dislocations. Plastic inorganic materials, for example, ionic crystals (insulators), ZnS in darkness, and Ag2S, are discussed in detail in terms of their prominent mechanical properties and potential applications. We conclude the article with several key scientific and technological questions to address in the future study. [ABSTRACT FROM AUTHOR]

Cu‐Fe‐S‐based compounds gain the interest from thermoelectric community because all the consisting elements, Cu, Fe, and S, are non‐toxic and earth‐abundant. Comparing with CuFeS2 and Cu5FeS4, the investigation on Cu9Fe9S16 is very rare. In this work, a series of Cu9–xFe9+xS16 samples were fabricated by means of melting‐annealing process. Their phase composition, microstructure, electrical and thermal transport properties were systematically investigated. X‐ray measurement confirms that all samples are phase pure. Transmission electron microscopy characterization indicates that the fabricated Cu9Fe9S16 has a natural nanostructure. Cu9Fe9S16 shows semiconducting‐like electrical transport behavior and intrinsically low lattice thermal conductivity. Beyond the numerous boundaries between nanosized grains, the existence of low‐frequency optical phonons is also responsible for the intrinsically low lattice thermal conductivity. Doping Fe at the Cu‐sites in Cu9Fe9S16 significantly alters the electrical transport properties by introducing extra carriers. A peak dimensionless figure of merit zT value of 0.21 is obtained at 800 K for pure Cu9Fe9S16, which is comparable with that for CuFeS2. [ABSTRACT FROM AUTHOR]

Cu‐Fe‐S‐based compounds gain the interest from thermoelectric community because all the consisting elements, Cu, Fe, and S, are non‐toxic and earth‐abundant. Comparing with CuFeS2 and Cu5FeS4, the investigation on Cu9Fe9S16 is very rare. In this work, a series of Cu9–xFe9+xS16 samples were fabricated by means of melting‐annealing process. Their phase composition, microstructure, electrical and thermal transport properties were systematically investigated. X‐ray measurement confirms that all samples are phase pure. Transmission electron microscopy characterization indicates that the fabricated Cu9Fe9S16 has a natural nanostructure. Cu9Fe9S16 shows semiconducting‐like electrical transport behavior and intrinsically low lattice thermal conductivity. Beyond the numerous boundaries between nanosized grains, the existence of low‐frequency optical phonons is also responsible for the intrinsically low lattice thermal conductivity. Doping Fe at the Cu‐sites in Cu9Fe9S16 significantly alters the electrical transport properties by introducing extra carriers. A peak dimensionless figure of merit zT value of 0.21 is obtained at 800 K for pure Cu9Fe9S16, which is comparable with that for CuFeS2. [ABSTRACT FROM AUTHOR]

Thermal conductivity is one of the most fundamental properties of materials with the value being determined by nearly all-scale structural features and multiple physical processes. Rapidly judging material's thermal conductivity is extremely important but challenging for the applications. The material genome paradigm offers a revolutionary way to efficiently screen and discover materials with designed properties by using accessible indicators. But such a performance indicator for thermal conductivity is quite difficult to propose due to the existence of multiple mechanisms and processes, especially for the materials with complex structures such as chalcogenides. In this study, the number mismatch between cations and anions is proposed as a practical performance indicator for lattice thermal conductivity in complex copper and silver chalcogenides, which can be used to explain the observed experimental data and find new low thermal conductivity materials. Such a number mismatch brings about rich phenomena to affect thermal conductivity including the complication of the unit cell and the creation of chemical hierarchy, point defects, rattling modes and lone-pair electrons. It is expected that this rich-connotation performance indicator can be also extended to other complex materials to discover designed thermal conductivities. [ABSTRACT FROM AUTHOR]

Copper sulfides have attracted great attention recently in the thermoelectric community due to the liquid-like behavior of Cu ions. Among the numerous copper sulfides, digenite Cu1.80S has a poorer thermoelectric performance but better stability than the state-of-the-art binary copper sulfide Cu1.97S. In this study, good stability and high thermoelectric performance were simultaneously obtained in Fe-doped Cu1.80S. Because Fe ions will not form a concentration gradient under an external field to change the critical voltage, Fe-doped Cu1.80S samples inherit the good stability of the pristine Cu1.80S. The critical voltage for Cu1.80Fe0.064S is 0.16 V at 750 K, which has been the largest value reported so far. Likewise, the Fe dopants can significantly improve the thermoelectric performance by suppressing the too high electrical conductivity of Cu1.80S. The peak dimensionless figure of merit (zT) for Cu1.80Fe0.064S is around 0.8 at 750 K, about four times that of Cu1.80S. The average zT for Cu1.80Fe0.064S is 0.40 in 300–750 K, which is amongst the highest values in reported thermoelectric sulfides. Combining the good stability and high thermoelectric performance, the present Cu1.80Fe0.064S has great potential to be used in the application of waste heat harvesting in the middle temperature range. [ABSTRACT FROM AUTHOR]