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Balancing the contradictory relationship between thermoelectric parameters, such as effective mass and carrier mobility, is a challenge to optimize thermoelectric performance. Herein, the exceptional thermoelectric performance is realized in GeTe through collaboratively optimizing the carrier and phonon transport via stepwise alloying Pb and CuSbSe2. The formation energy of Ge vacancy is efficiently bolstered by alloying Pb, which reduces carrier density and carrier scattering to maintain superior carrier mobility in GeTe. Additionally, CuSbSe2, acting as an n‐type dopant, further modulates carrier density and validly equilibrates carrier mobility and effective mass. Accordingly, the promising power factor of 45 µW cm−1 K−2 is achieved at 723 K. Meanwhile, point defects are found to significantly suppress phonons transport to descend lattice thermal conductivity by Pb and CuSbSe2 alloying, which barely impacts the carrier mobility. A combination with superior carrier mobility and lower lattice thermal conductivity, a maximum ZT of 2.2 is attained in Ge0.925Pb0.075Cu0.005Sb0.005TeSe0.01, which corresponds to a 100% promotion compared with that of intrinsic GeTe. This study provides a new indicator for optimizing carrier and phonon transport properties by balancing interrelated thermoelectric parameters. [ABSTRACT FROM AUTHOR]

Compared with p -type oxyselenide thermoelectric material, the corresponding n -type material research progress is slow. In this work, combining low thermal conductivity of BiCuSeO and high electron carrier concentration of n -type Bi 2 O 2 Se, a new-type two-dimensional layered oxyselenide Bi 6 Cu 2 Se 4 O 6 was synthesized. Through increasing electron carrier concentration via introducing transition metal elements (Ti, Zr, Ce), the electrical transport properties were enhanced and the peak ZT value ~ 0.16 at 873 K was obtained, which is 60 % higher than that in Bi 6 Cu 2 Se 3.6 Cl 0.4 O 6. This work indicates that transition metal element is an effective n -type dopant to enhance the thermoelectric performance of Bi 6 Cu 2 Se 4 O 6. The new-type 2D layered oxyselenide Bi 6 Cu 2 Se 4 O 6 can be synthesized by intercalating BiCuSeO and Bi 2 O 2 Se layers with a 1:2 ratio along the c -axis. Through introducing transition metal elements, a 60 % improvement of peak ZT value (~ 0.16 at 873 K) can be reached in Bi 5.9 Zr 0.1 Cu 2 Se 3.6 Cl 0.4 O 6. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work we investigated the thermoelectric transport behaviors of p -type PbS and n -type PbS with an emphasis on its contrasting electronic band structures. We found that the Seebeck coefficients of p -type PbS increased faster with rising temperature than that of n -type PbS with the same carrier concentration. The Density functional theory (DFT) calculation of the energy band structure of PbS as a function of temperature illustrates a significant contribution from multiple valence bands in K-doped p -type PbS. This work revealed one important information that manipulating electronic bands is also suitable in developing high-performance PbS thermoelectric systems. PbS possesses both multiple conduction bands and multiple valence bands. With rising temperature, valence bands illustrate a more pronounced converging trend than conduction bands, which results in higher Seebeck coefficients in p -type PbS at 523–823 K than that of n -type PbS with the same carrier concentration. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Tin sulfide (SnS), a typical IV–VI compound with low-cost, abundant-earth and eco-friendly elements, has aroused widespread attentions in the thermoelectric community due to its similar electron and phonon structures with SnSe. However, undoped SnS possesses the features of low carrier concentration and inferior band structures, which produces indecent thermoelectric performance. In this work, we successfully resolved these shortcomings of SnS through stepwise Na doping and Se alloying. Firstly, the carrier concentration of SnS was increased and optimized through Na doping, which leads to an enhancement both in electrical conductivity and Seebeck coefficients through activating multiple valance bands. Secondly, the electronic band structure of SnS was modified through Se alloying, both narrowing band gap and flatting valence band shape contribute excellent electrical transport properties, resulting in maximum power factor ∼6.0 μWcm−1K−2. After synergistically optimizing interdependent thermoelectric parameters through Na doping and Se alloying, a record high ZT of 0.70 at 873 K was obtained in polycrystalline SnS. Our work indicates that SnS is one of very promising earth-abundant thermoelectric materials for power generation in mediate-temperature range. • Power factor of p -type SnS was improved from 2.5 μWcm−1K−2 to 4.8 μWcm−1K−2 at 923 K through Na doping. • Power factor of p -type SnS was improved from 4.8 μWcm−1K−2 to 6.0 μWcm−1K−2 at 873 K through Se alloying. • ZT max of p -type SnS is distinctly enhanced from 0.25 to 0.70 at 873 K after Na doping and Se alloying. [ABSTRACT FROM AUTHOR]

Abstract SnSe crystals were reported to possess extraordinary thermoelectric performance, while the polycrystals were less marked due to the inferior carrier and phonon transport properties. Herein, we fully take advantage of the complex band structure and strong point scattering via alloying SnS. The carrier concentration and Seebeck coefficient were synergistically optimized via activating multiple valance bands and enlarging band effective mass, which contribute to a maximum power factor ∼7.53 μWcm−1K−2 at 793 K. Meanwhile, the lattice thermal conductivity was greatly reduced to ∼0.92 Wm−1K−1 due to the effective phonon scattering from point defects, as well demonstrated by the Callaway model. Combining a high power factor with low thermal conductivity, relatively high ZT of 1.2 at 793 K was obtained in polycrystalline Sn 0.98 Na 0.02 Se 0.9 S 0.1. Our work demonstrates that alloying is simple yet effective approach for enhancing thermoelectric performance for polycrystalline SnSe, and SnSe system is one of promising thermoelectric candidates. Graphical abstract SnSe crystals possess excellent thermoelectric performance and motivate us to enhance the thermoelectric properties of polycrystalline SnSe. Here, through band structure modification and strong point scattering in polycrystalline SnSe with Na doping and SnS alloying, we achieved a maximum ZT of ∼1.2 at 793 K in Sn 0.98 Na 0.02 Se 0.9 S 0.1 and theoretical prediction demonstrated higher thermoelectric performance with an optimum carrier concentration. Image 1 Highlights • Power factor of p -type polycrystalline SnSe was improved to ∼7.53 μWcm−1K−2 at 793 K through SnS alloying. • Lattice thermal conductivity of p -type polycrystalline SnSe was reduced to ∼0.92 Wm−1K−1 through SnS alloying. • ZT max of p -type polycrystalline SnSe was enhanced from ∼0.6 to ∼1.2 through SnS alloying. [ABSTRACT FROM AUTHOR]

Cubic SnSe has been recognized as one of the most promising mid-temperature thermoelectric candidates. Herein, the cubic-phase SnSe has been stabilized at room temperature by alloying NaSbSe 2 and NaSbTe 2 , respectively, and the contrasting thermoelectric properties of SnSe-NaSbSe 2 and SnSe-NaSbTe 2 were systematically investigated. NaSbTe 2 -alloyed SnSe demonstrates better performance with especially higher electrical properties. According to the DFT calculations, the introduction of NaSbTe 2 can bring the lattice parameter of cubic-phase SnSe closer to SnTe, leading to a lower cation vacancy formation energy and producing an ultra-high hole carrier concentration. Meanwhile, Te has a more developed charge density compared with that of Se, providing additional channels for charge transport when bonded to Sn atoms in cubic lattice. Limited by the electrical transport properties, the ZT max for SnSe-NaSbSe 2 only reaches ∼ 0.50 at 773 K, while the ZT max for SnSe-NaSbTe 2 approaches ∼ 0.95. Furthermore, sodium doping was utilized to tune the carrier mobility and carrier concentration of SnSe-NaSbTe 2. Resultantly, the PF max and ZT max values reach ∼ 11 μW cm−1 K−2 and ∼ 1.20 at 773 K in sodium-doped SnSe-NaSbTe 2 , 4.4 and 3.0 times higher than those of pure SnSe, respectively. Our study further promotes cubic-phase SnSe thermoelectrics for mid-temperature energy harvesting applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Oxygen-containing semiconductors are considered to be promising thermoelectric materials because of the high physicochemical stability. New layered oxyselenide Bi 6 Cu 2 Se 4 O 6 possesses intrinsic low lattice thermal conductivity and can be modulated to n -type semiconductor through halogen doping, which is considered as a potential n -type thermoelectric oxide. In this work, first-principles calculations are utilized to obtain the electronic and phonon band structures for deeply recognizing the transport features of intrinsic Bi 6 Cu 2 Se 4 O 6. Furthermore, Nb is selected as donor dopant in Bi 6 Cu 2 Se 3.6 Cl 0.4 O 6 , realizing a significantly improved power factor of ∼ 4.3 μV cm−1 K−2, which originates from the simultaneously optimized carrier concentration by effective doping and strengthened effective mass by inducing resonant levels around Fermi level. Meanwhile, the enhancement of phonon scattering are introduced, leading to a low lattice thermal conductivity of ∼ 0.68 W m−1 K−1. Finally, thanks to the effective doping of Nb and the introduction of resonant levels, a maximum ZT ∼ 0.4 at 873 K and an average ZT ∼ 0.21 from 303 to 873 K can be obtained in n -type Bi 5.91 Nb 0.09 Cu 2 Se 3.6 Cl 0.4 O 6. This study broadens the applicability of resonant levels to optimize performances of thermoelectric oxides, and promotes the potential application of n -type Bi 6 Cu 2 Se 4 O 6 -based thermoelectric materials in medium temperature range. [Display omitted] [ABSTRACT FROM AUTHOR]

BiSbSe 3 is a promising medium-temperature thermoelectric material on account of its intrinsically low thermal conductivity. To further enhance the thermoelectric performance in n -type BiSbSe 3 , we conduct Br doping at Se sites to optimize its carrier concentration and electrical conductivity, finally a maximum ZT of ∼0.8 in nanostructured BiSb(Se 0.94 Br 0.06) 3 is obtained at 700 K through mechanical alloying. Based on the optimal BiSb(Se 0.94 Br 0.06) 3 composition, we perform percolation effect with mixed grain sizes in nanoscale and microscale to enhance carrier mobility. It is found that carrier mobility is favorably improved by the addition of microscale grains (∼30 μm) in nanostructured BiSb(Se 0.94 Br 0.06) 3 matrix due to the reduced grain boundaries to carrier scattering, which benefits high electrical conductivity and power factor. Simultaneously, the BiSb(Se 0.94 Br 0.06) 3 matrix with mixed grain sizes still maintains very low thermal conductivity due to its intrinsically strong lattice anharmonicity. Owing to the optimized electrical properties and maintained low thermal conductivity, we obtain a maximum ZT value of ∼1.0 at 700 K in BiSb(Se 0.94 Br 0.06) 3 –4C matrix with 40% microscale grains. This work provides a feasible method to optimize thermoelectric performance by designing microstructure with percolation effect. • Carrier concentration was improved to ∼1.91 × 1020 cm−3 in n -type BiSbSe 3 by Br doping. • PF max of n -type BiSbSe 3 was significantly enhanced to ∼6.0 μW cm−1 K−2 at 700 K through improving carrier mobility via utilizing percolation. • ZT max of n -type BiSbSe 3 was enhanced from ∼0.1 to ∼1.0 at 700K. [ABSTRACT FROM AUTHOR]

The n -type PbTe still maintains relatively low thermoelectric performance compared with its p -type counterpart. Thus, to promote its performance in n -type PbTe, we conduct successive strategies that firstly suppressing the lattice thermal conductivity (κ lat) through alloying with ternary compound AgSbSe 2 , and then optimizing carrier density with Sb, Bi or I doping. In AgSbSe 2 -alloyed PbTe samples, the κ lat can be evidently reduced, and the minimum κ lat decreases from ∼1.1 Wm−1K−1 in undoped PbTe to ∼0.8 Wm−1K−1 in PbTe–5%AgSbSe 2. Based on PbTe–5%AgSbSe 2 matrix, several dopants (Sb, Bi or I) are used to optimize its carrier density, and found that I element is verified to be the most effective dopant to enhance its electrical transport properties. In I-doped PbTe–5%AgSbSe 2 samples, the carrier density raises from ∼2.49 × 1016 cm−3 in PbTe–5%AgSbSe 2 to ∼1.15 × 1019 cm−3 in PbTe 0.992 I 0.008 -5%AgSbSe 2 , which contributes to the maximum power factor ∼14.8 μWcm−1K−2. Combining the reduced lattice thermal conductivity and improved power factor, the maximum ZT max and average ZT ave values in PbTe 0.992 I 0.008 -5%AgSbSe 2 are boosted to ∼1.0 at 723 K and ∼0.77 at 300–823 K, respectively. This work points out a valid avenue to improve thermoelectric transport property in n -type PbTe with separately successive strategies to adjust its thermal and electrical performance. • κ min ∼0.8 Wm−1K−1 was achieved in n -type PbTe through introducing AgSbSe 2. • PF max of n -type PbTe was significantly enhanced from ∼3.4 μWcm−1K−2 to ∼14.8 μWcm−1K−2 by I doping. • ZT max of n -type PbTe was enhanced from ∼0.45 to ∼1.00. [ABSTRACT FROM AUTHOR]

In this work, the thermoelectric performance of p -type PbS was boosted remarkably through Na doping and introducing Cu 2 S. Firstly, the electrical transport properties (power factor) of p -type PbS was optimized via Na doping, and the maximum ZT ∼ 0.67 was achieved in Pb 0.98 Na 0.02 S. Secondly, the total thermal conductivity of Pb 0.98 Na 0.02 S was suppressed through introducing Cu 2 S by means of significantly reducing the electronic thermal conductivity by 80% at 823 K through Cu counter-doping, meanwhile, the power factor of Pb 0.98 Na 0.02 S was further enhanced through optimizing carrier concentrations via introducing Cu. The combination of decreasing total thermal conductivities and the optimizing power factors leads to peak ZT ∼1.2 at 823 K in p -type Pb 0.98 Na 0.02 S–2%Cu 2 S. Present results illustrate that introducing Cu 2 S is an effective method to enhance the thermoelectric performance of p -type PbS through decreasing the electronic thermal conductivity which also has great potential in other thermoelectric materials system. • Thermoelectric performance of p -type PbS was remarkably boosted by reducing electronic thermal conductivity κ ele. • κ ele of p -type Pb 0.98 Na 0.02 S was reduced by 80% from ∼0.53 W m−1K−1 to ∼ 0.11 W m−1K−1 at 823 K with introducing Cu 2 S. • The maximum ZT ∼1.2 at 823 K was realized in p -type Pb 0.98 Na 0.02 S–2%Cu 2 S. [ABSTRACT FROM AUTHOR]

PbTe-based thermoelectric materials are considered to be a medium-temperature thermoelectric candidates and the high-performance n -type PbTe is urgently to be developed to match its p -type counterpart on account of practical application. Herein, we firstly optimized the carrier density of n -type PbTe through Sb doping, and obtained a maximum ZT value of ∼1.0. Then, based on the optimized carrier density, we introduced ternary compounds AgSb(Se, Te) 2 to suppress the lattice thermal conductivity. Minimum lattice thermal conductivity of n -type PbTe was reduced as low as ∼0.53 W m−1K−1 and ∼0.62 Wm−1K−1 through introducing AgSbSe 2 and AgSbTe 2 , respectively. Combining the maintained electrical properties with suppressed thermal conductivity, maximum ZT values ∼1.2 and ∼1.3 were obtained in PbTe+2%AgSbSe 2 and PbTe+2%AgSbTe 2 , respectively. This work provides an effective strategy of synergistically balancing charge and phonon transports in n -type PbTe with ternary AgSb(Se, Te) 2 compounds. • κ min of n -type PbTe was reduced to ∼ (0.53–0.62) Wm−1K−1 through introducing AgSb(Se, Te) 2. • Power factor ∼20.0 μWcm−1K−2 was realized in n -type PbTe through maintaining carrier mobility. • ZT max of n -type PbTe was enhanced from ∼1.0 to ∼ (1.17–1.25). [ABSTRACT FROM AUTHOR]