We report the high thermoelectric performance of p-type polycrystalline SnSe obtained by the synergistic tailoring of band structures and atomic-scale defect phonon scattering through (Na,K)-codoping. The energy offsets of multiple valence bands in SnSe are decreased after Na doping and further reduced by (Na,K)-codoping, resulting in an enhancement in the Seebeck coefficient and an increase in the power factor to 492 μW m K. The lattice thermal conductivity of polycrystalline SnSe is decreased by the introduction of effective phonon scattering centers, such as point defects and antiphase boundaries. The lattice thermal conductivity of the material is reduced to values as low as 0.29 W m K at 773 K, whereas ZT is increased from 0.3 for 1% Na-doped SnSe to 1.2 for 1% (Na,K)-codoped SnSe.

State-of-the-art halide perovskite solar cells have bandgaps larger than 1.45 eV, which restricts their potential for realizing the Shockley-Queisser limit. Previous search for lowbandgap (1.2 to 1.4 eV) halide perovskites has resulted in several candidates, but all are hybrid organic-inorganic compositions, raising potential concern regarding device stability. Here we show the promise of an inorganic low-bandgap (1.38 eV) CsPb 0.6 Sn 0.4 I 3 perovskite stabilized via interface functionalization. Device efficiency up to 13.37% is demonstrated. The device shows high operational stability under one-sun-intensity illumination, with T 80 and T 70 lifetimes of 653 h and 1045 h, respectively (T 80 and T 70 represent efficiency decays to 80% and 70% of the initial value, respectively), and long-term shelf stability under nitrogen atmosphere. Controlled exposure of the device to ambient atmosphere during a long-term (1000 h) test does not degrade the efficiency. These findings point to a promising direction for achieving low-bandgap perovskite solar cells with high stability.

Bismuth sulfide (BiS) has been of high interest for thermoelectric applications due to the high abundance of sulfur on Earth. However, the low electrical conductivity of pristine BiS results in a low figure of merit (ZT). In this work, BiS@Bi core-shell nanowires with different Bi shell thicknesses were prepared by a hydrothermal method. The core-shell nanowires were densified to Bi/BiS nanocomposite by spark plasma sintering (SPS), and the structure of the nanowire was maintained as the nanocomposite due to rapid SPS processing and low sintering temperature. The thermoelectric properties of bulk samples were investigated. The electrical conductivity of a bulk sample after sintering at 673 K for 5 min using BiS@Bi nanowire powders prepared by treating BiS nanowires in a hydrazine solution for 3 h is 3 orders of magnitude greater than that of a pristine BiS sample. The nanocomposite possessed the highest ZT value of 0.36 at 623 K. This represents a new strategy for densifying core-shell powders to enhance their thermoelectric properties.

SnSe has attracted much attention due to the excellent thermoelectric (TE) properties of both p-and n-type single crystals. However, the TE performance of polycrystalline SnSe is still low, especially in n-type materials, because SnSe is an intrinsic p-type semiconductor. In this work, a three-step doping process is employed on polycrystalline SnSe to make it n-type and enhance its TE properties. It is found that the Sn 0.97 Re 0.03 Se 0.93 Cl 0.02 sample achieves a peak ZT value of ≈1.5 at 798 K, which is the highest ZT reported, to date, in n-type polycrystalline SnSe. This is attributed to the synergistic effects of a series of point defects: × × V V , Cl , ,Re ,Re Se .. Se . Sn ,, Sn 0 . In those defects, the V Se .. compensates for the intrinsic Sn vacancies in SnSe, the Cl Se .acts as a donor, the V Sn ,, acts as an acceptor, all of which contribute to optimizing the carrier concentration. Rhenium (Re) doping surprisingly plays dual-roles, in that it both significantly enhances the electrical transport properties and largely reduces the thermal conductivity by introducing the point defects, × × Re , Re Sn 0 . The method paves the way for obtaining high-performance TE properties in SnSe crystals using multipoint-defect synergy via a step-by-step multielement doping methodology.

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Thermal barrier coatings (TBCs) are one of the most important materials in gas turbine to protect the high temperature components. RETa3O9 compounds have a defect‐perovskite structure, indicating that they have low thermal conductivity, which is the critical property of TBCs. Herein, dense RETa3O9 bulk ceramics were fabricated via solid‐state reaction. The crystal structure was characterized by X‐ray diffraction (XRD) and Raman Spectroscope. Scanning electron microscope (SEM) was used to observe the microstructure. The thermophysical properties of RETa3O9 were studied systematically, including specific heat, thermal diffusivity, thermal conductivity, thermal expansion coefficients, and high‐temperature phase stability. The thermal conductivities of RETa3O9 are very low (1.33‐2.37 W/m·K, 373‐1073 K), which are much lower than YSZ and La2Zr2O7; and the thermal expansion coefficients range from 4.0 × 10−6 K−1 to 10.2×10−6 K−1 (1273 K), which is close to La2Zr2O7 and YSZ. According to the differential scanning calorimetry (DSC) curve there is not phase transition at the test temperature. Due to the high melting point and excellent high‐temperature phase stability with these oxides, RETa3O9 ceramics were promising candidate materials for TBCs.

Digenite (Cu1.8S) as a potential p-type thermoelectric (TE) material has attracted extensive attention due to its environmental-friendliness and low toxicity.

α-Mg 3 Sb 2 is an excellent thermoelectric material through excess-Mg addition and n-type impurity doping to overcome its persistent p-type behavior. It is generally believed that the role of excess-Mg is to compensate the single Mg vacancy to realize n-type carrier conduction. In contrary to this belief, the present work indicates that the role of excess-Mg is to compensate the electronic charge of defect complex (V Mg(2) + Mg I ) 1− . The Mg solubility in α-Mg 3+x Sb 2 is quite small when only considering a single defect, but it enlarged up to x = 0.011 with the defect complex (V Mg(2) + Mg I ) 1− , which is more reasonable as supported by experiments. Under Mg-poor conditions, V Mg(1) 2− and V Mg(2) 2− are the dominant defects, and their concentrations can reach (1.05−1.18) × 10 19 cm −3 at 1200 K. Under Mg-rich conditions, (V Mg(2) + Mg I ) 1− is found to be the dominant reason for strong p-type behavior, and their concentrations can reach as high as 3.5 × 10 20 cm −3 , which shifts the Fermi level closer to the valence band maximum. The predicted carrier concentrations in the range 10 17 −10 20 cm −3 are in the same range found experimentally for pure p-type α-Mg 3 Sb 2 .