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In recent years, BiCuSeO oxyselenides have been developed as a promising thermoelectric material. In this article, PbxBi1−xCu1−ySeO (x = y = 0, 0.02, 0.04, 0.06, and 0.08) are prepared by solid‐state reaction method and spark plasma sintering (SPS), and the combinatorial effects of Pb doping and Cu deficiencies on thermoelectric properties are investigated systematically. The transport properties are significantly enhanced due to the optimized carrier density, majorly contributing to the promotion of ZT values. As a result, the maximum ZT of 0.77 at 873 K and average ZT (from 300 to 873 K) of 0.50 are obtained for Pb0.06Bi0.94Cu0.94SeO sample. The values are 0.4 and 1.2 times, respectively, higher than that of pristine sample. [ABSTRACT FROM AUTHOR]

We offered a new and simple routine for significant reducing lattice thermal conductivity and improve the thermoelectric properties of Bi 2 Te 3 materials. Dense dislocations were introduced by means of adding excess Te into Bi 2 Te 3 powder by combining ball milling and spark plasma sintering (SPS). During the high temperature SPS process, excess Te spilled out of the die. The ultra-low lattice thermal conductivity of Bi 2 Te 3 was achieved due to the enhanced phonon scattering by dislocations. The highest ZT value of 0.7 at 398 K was obtained for a pure Bi 2 Te 3 bulk sample which is 175% higher than that of pristine Bi 2 Te 3 sample. [ABSTRACT FROM AUTHOR]

We report the effect of Bi 3+ doping on both electron and phonon transport properties of Bi x Cu 1.8- x S ( x = 0, 0.004, 0.01, 0.014, 0.02) superionic conductors. An enhanced ZT value in different degrees with x is mainly attributed to an improved electrical conductivity owing to an increased carrier mobility with an undegrated Seebeck coefficient when 0 ≤ x ≤ 0.01, and a reduced thermal conductivity to a low level (0.71–1.00 Wm −1 K −1 ) at x = 0.02 benefiting by the formation of the low-conductive Cu 3 BiS 3 and Cu 1.96 S second phases. The highest ZT value of 0.61 at 673 K obtained for the Bi 0.01 Cu 1.79 S ( x = 0.01) sample, which is twice as large as that of the pure Cu 1.8 S sample. Our result indicates that the introduction of Bi 3+ in thermoelectric materials is an effective and convenient strategy to improve ZT by improving the power factor and/or decreasing thermal conductivity. [ABSTRACT FROM AUTHOR]

Cu 1.8 Se 1− x S x (0 ≤ x ≤ 1) thermoelectric alloys were prepared by mechanical alloying (MA) combined with spark plasma sintering (SPS) technology. The phase structure and morphologies of all the samples were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The electrical conductivity, Seebeck coefficient, thermal conductivity were investigated for all the Cu 1.8 Se 1− x S x alloys with a special emphasis on the influence of the S doping. With the increasing of S contents, a phase transition of Cu 1.8 Se 1− x S x was occurred from cubic to hexagonal. The electrical and thermal transport properties of the samples changed accordingly. The Cu 1.8 Se 0.7 S 0.3 alloy achieves the highest ZT of 0.78 at 773 K due to both optimized electrical transport properties and thermal transport properties, which is 44% higher than that of pristine Cu 1.8 S (0.54 at 773 K) and 95% higher than that of pristine Cu 1.8 Se (0.4 at 773 K). [ABSTRACT FROM AUTHOR]

Thermoelectric (TE) materials can interconvert waste heat into electricity, thus are promising for power generation and solid-state refrigeration. The thermoelectric properties of a certain material strongly correlate with its chemical, structural and electronic features; therefore, a thorough characterization of these features is not only crucial to profoundly understand the material itself, but also helps to design new materials with desired properties. Under this circumstance, various electron microscopy (EM) techniques are developed, from micro-scale to atomic-scale, two-dimensional (2-D) to 3-D, and static to dynamic. In this review, we review advanced EM techniques already applied in and also look into the perspective of introducing more EM techniques into the field of thermoelectrics. Specifically, we firstly summarize “what have been done” involving: structural and chemical characterizations of all-scale “imperfectness”, electronic structure investigation, 3-D morphology and dynamic evolution of nanostructures, and atomic-scale mapping of Seebeck coefficient and defects; based on these characterized features, we then briefly review the calculations on electrical and thermal transport properties to illustrate the structure–property correlations. In what follows, we propose “what can be done” in TEs via EM techniques including: valence-electron distribution, quantitative measurement of atomic displacement, point defect characterization, local band gap measurement, phonon excitation detection, electrostatic potential determination, thermal stability of nanostructures, and in-situ observation and measurement of local TE effects. [ABSTRACT FROM AUTHOR]

Cu 1.97 Se- x wt. % In 2 O 3 (x = 0–1) bulk composites are fabricated by combining high-temperature melting and spark plasma sintering technology. The doping of In3+in Cu vacancies tunes the carrier concentration and modifies the band structure of Cu 1.97 Se. Additionally, excessive In 2 O 3 particles benefit the construction of multiple lattice defects to strengthen phonon scattering and suppress the long-range migration of Cu ions, resulting in obviously reduced thermal conductivity and improved service stability. Ultimately, a peak ZT value of 1.43 is obtained at 873 K for the Cu 1.97 Se-0.5 wt. % In 2 O 3 bulk specimen, which is almost 150% higher than that of pristine sample. The thermoelectric conversion efficiency and mechanical properties of the composites sample are also measured. The results suggest that Cu 1.97 Se-based nanocomposites offer potential for use in power generation device assembly. [ABSTRACT FROM AUTHOR]

P-type Cu1.8+xSe (x = 0, 0.16, 0.20) compounds were synthesized by mechanical alloying and spark plasma sintering technique. A 100% enhancement of the Seebeck coefficient was achieved in the whole temperature interval for x = 0.16 and x = 0.20 bulks compared with that of the x = 0 bulk. The thermal conductivity was all below 1.6 W m−1 K−1 in the whole temperature interval for x = 0.16 and x = 0.20 bulks, showing a pronounced reduction compared with that of the x = 0 bulk. The lowest thermal conductivity 0.69 W m−1 K−1 was achieved in the x = 0.16 sample at 773 K, whereby a maximum ZT value of 1.23 was obtained, revealing that optimizing Cu content in Cu1.8+xSe system is an effective method to improve the thermoelectric (TE) merit and indicating a great potential for TE application along with their nontoxicity and low cost. [ABSTRACT FROM AUTHOR]

Abstract: Bi2−x Ag3x S3 (x =0–0.06) polycrystals were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). The phase, microstructure, electrical and thermal transport properties were investigated with a special emphasis on the influence of Ag doping content. All the Bi2−x Ag3x S3 powders can be indexed as single phase with an orthorhombic symmetry, a second AgBi3S5 phase in SPSed bulks occurs as the doping contents x ≥0.02, which enhances the electrical conductivity, resulting in improvement of electrical transport properties for Bi2−x Ag3x S3 bulk samples. A maximum ZT value reached 0.23 at 573K for the Bi1.99Ag0.03S3 sample, which is 130% higher than that (0.11) of the pure Bi2S3. [Copyright &y& Elsevier]

Bi 2 S 3 with earth abundant elements has been considered as a potential thermoelectric material. However, it is challenging to make Bi 2 S 3 materials as a promising high-performance thermoelectric device due to its poor electrical transport properties and the coupling between its electrical and thermal transport properties. In this work, we present a new strategy that can significantly improve electrical transport properties, as well as reduce the lattice thermal conductivity by carrier modulation and introducing multi-nano-precipitates in PbBr 2 doped Bi 2 S 3 bulk samples. The electrical conductivity of Bi 2 S 3 was boosted more than one order magnitude higher than that of pristine Bi 2 S 3 after the introducing of Pb and Br, which is demonstrated as the replacement form at the sites of Bi and S, respectively. The resultant Bi 2 S 3 shows an enhanced high power factor of 690 μWm-1K-1 at 598 K, three times higher than that in pristine samples. Besides, the lattice thermal conductivity was reduced to 0.35 Wm-1K-1 at 673 K due to multi-nano-precipitates synergy, i.e., Bi 2 (S 1-x Br x) 3 and (Bi 1-y Pb y) 2 S 3 nanoprecipitates in the Bi 2 S 3 matrix. A high ZT of ~0.8 was therefore achieved at 673 K for Bi 2 S 3 with 1.5 mol% PbBr 2 , a record value in the state-of-the-art Bi 2 S 3 system. A record ZT value in the state-of-the-art Bi 2 S 3 system of ~0.8 was therefore achieved at 673 K for Bi 2 S 3 doped with 1.5 mol% PbBr 2. Image 1 • The Bi 2 S 3 specimens were fabricated via solid-state melting method followed by SPS. • The properties of Bi 2 S 3 was optimized by carrier modulation and introducing multi-precipitates. • Multi-nano-precipitates significantly reduce the lattice thermal conductivity of Bi 2 S 3. • A record ZT of 0.8 is obtained for Bi 2 S 3 doped with 1.5 mol% PbBr 2 at 673 K. [ABSTRACT FROM AUTHOR]

Digenite (Cu 1.8 S) has attracted extensive attention as a candidate for use in thermoelectric applications owing to its low cost and low toxicity, but its thermoelectric (TE) properties are still poor. In this study, Pb doping was used to improve the TE properties of Cu 1.8 S polycrystalline materials. Pb-doped Cu 1.8 S was fabricated using mechanical alloying (MA) and the spark plasma sintering (SPS) technique. The effects of Pb doping on the TE properties of Cu 1.8 S were investigated in detail. The power factor of Cu 1.8 S was maintained upon the introduction of Pb owing to an improved Seebeck coefficient and slightly reduced electrical conductivity. A maximum TE figure of merit (ZT) value of 0.77 was attained at 773 K for a Pb 0.01 Cu 1.79 S sample, which was 1.57 times higher than that of a pristine Cu 1.8 S sample. Image 1 • Pb doped Cu 1.8 S samples were fabricated by MA + SPS method. • Pb doping introduced electrons to the Cu 1.8 S matrix. • PbS second phase in Cu 1.8 S benefits to reduce the thermal conductivity. • A maximum ZT of 0.77 was attained at 773 K for a Pb 0.01 Cu 1.79 S sample. [ABSTRACT FROM AUTHOR]

Digenite (Cu 1.8 S) has attracted extensive attention as candidate for use in thermoelectric applications due to its low-cost, low-toxicity characteristics, but the thermoelectric (TE) property is still not good. In this work, PbS was used for improving TE properties of polycrystalline Cu 1.8 S bulk. Cu 1.8 S+ x wt% PbS ( x  = 0, 0.5, 1, 2, 3) bulk samples were fabricated via mechanical alloying (MA) and spark plasma sintering (SPS) techniques. The effects of adding PbS on the TE performance of Cu 1.8 S were investigated in detail at the temperature between 323 K and 773 K. According to the results, introducing PbS is an efficient approach for optimizing the TE properties of Cu 1.8 S, which is mainly due to the maintained electrical transport properties by the regulated hole carrier concentration and the modified band structure, as well as the reduced the thermal conductivity by the generated point defect and additional interfaces. An optimum thermoelectric figure of merit ( ZT ) value of 1.1 was obtained at 773 K for the Cu 1.8 S sample with 2 wt% PbS, which is 2.2 times higher than that of the pristine Cu 1.8 S (0.49 at 773 K). [ABSTRACT FROM AUTHOR]

The electrical conductivity, Seebeck coefficient and thermal conductivity of the Cu 1−x In 1−y Se 2.05 alloys were investigated, which were synthesized by solid-state reaction method combined with spark plasma sintering (SPS) technique. With the increasing of vacancy contents, the electron and phonon scattering were enhanced. The electrical and thermal transport properties of the samples changed accordingly. The Cu 0.99 InSe 2.05 bulk sample achieves the highest ZT value of 0.31 at 773 K due to optimized electrical and thermal transport properties, which is 3 times higher than that of pristine CuInSe 2.05 . Moreover, it is the highest ZT value in CuInSe 2 system in all of previous literatures. [ABSTRACT FROM AUTHOR]

Copper selenide can be used in thermoelectric applications since it has the features of a superionic conductor. Nevertheless, improving its electrical and thermal transport properties using facile fabrication is challenging. Herein, a one-stone and three-bird strategy was proposed for enhancing the thermoelectric performance of Cu 2 Se-based composites. Natural verdigris was used as an additive to construct a porous structure simultaneously while introducing Cu vacancies and multiscale Cu 2 O precipitates in the Cu 2-x Se material. The carrier concentration was tailored to optimize the electrical transport properties of the bulk composites. Additionally, multiple lattice defects were generated in the bulk composites, benefiting the significantly reduced thermal conductivity. Ultimately, the Cu 2 Se-based composite achieved a peak ZT value of 1.25 at 873 K. This study provided a simple approach of adding a natural mineral to regulate the composition and microstructure of the material, which may be worth promoting in other systems. [Display omitted] • The strategy of adding natural verdigris is proposed. • The generated multiscale pores and precipitates reduce the lattice thermal conductivity. • The introduced Cu vacancies increase the carrier concentration of bulk composites. • Thermoelectric figure of merit of the bulk composite is 140 % higher than that of the pure Cu 2 Se. [ABSTRACT FROM AUTHOR]

Digenite (Cu 1.8 S), one of superionic conductors, possesses the exceptional electrical transports performance but unsatisfactory thermal transport properties, which desiderates to be improved to become the candidate for use in the field of thermoelectric application. The porous Cu 1.8 S based composites with Na 2 S polycrystalline bulk samples were prepared via the incorporation of mechanical alloying (MA) and spark plasma sintering (SPS) technique by employing Na 2 S·9H 2 O as a addictive. The hydrate assists to create a porous structure and to refine grains during the fabrication procedure. Benefiting from the strengthened phonons scattering by additional multiscale pores after introducing Na 2 S, the thermal conductivity was dramatically decreased which results in an overall increased thermoelectric efficiency. The optimal thermoelectric figure of merit (ZT) of 0.78 at 773 K is obtained for Cu 1.8 S+2 wt % Na 2 S sample, which is 60% higher than that (0.49) of pristine Cu 1.8 S. [ABSTRACT FROM AUTHOR]

Thermoelectric technology has been applied in the fields of industrial waste heat power generation, special spatial power supply, semiconductor chip cooling, advanced refrigeration, etc. Comparing to other thermoelectric material systems, bismuth telluride (Bi 2 Te 3) based thermoelectric materials are widely used in industrial and commercial fields due to their stable zT values and relatively high conversion efficiencies at room temperature range. However, the low hardness and easy dissociation of Bi 2 Te 3 materials lead to the waste of raw materials in industrial processing. Therefore, substantial efforts have been made to find a balance between the zT value and the hardness of bismuth telluride. In this study, the mechanical properties of commercial Bi 2 Te 3 were significantly enhanced by dispersing the second phase of the SiC particles in the matrix via a combined process of mechanical alloying (MA) and spark plasma sintering (SPS). Although the zT value of the composite was slightly decreased, the average hardness was increased from ~1.2 to 1.7 GPa, and the modulus of the composite was also improved. The thermal expansion rate and thermal expansion coefficients were also measured. The mechanism of the enhanced mechanical properties of the Bi 2 Te 3 was discussed in detail. This work offered a simple strategy for improving the machinability of commercial Bi 2 Te 3 , which is of high importance for the large scale industrial application of thermoelectric materials. [ABSTRACT FROM AUTHOR]

• The thermoelectric properties of natural chalcopyrite were investigated for the first time. • The TE properties of chalcopyrite were highly enhanced by vacuum annealing. • The natural chalcopyrite is a promising thermoelectric material. This paper focuses on the thermoelectric properties of natural chalcopyrite and provides methods for optimizing its thermoelectric properties. Natural chalcopyrite shows obvious anisotropic thermoelectric properties. Although the thermoelectric properties of natural chalcopyrite are low, they are found to be significantly enhanced by vacuum annealing. Natural chalcopyrite was proven to be feasible and potential thermoelectric materials. [ABSTRACT FROM AUTHOR]

Abstract A new approach was developed for enhancing the thermoelectric performance of In 2 O 3 (ZnO) 5 ceramics. Ni coating layer on the surface of In 2 O 3 (ZnO) 5 powders was prepared by chemical plating. The Ni-Coated In 2 O 3 (ZnO) 5 powders was densified to composite bulk with Ni enrichment in the grain boundaries. The composite sample obtained a remarkably enhanced dimensionless thermoelectric figure of merit (ZT) of 0.39 at 973 K, which is 3.6 times higher than that of a pristine In 2 O 3 (ZnO) 5 sample. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Copper Sulfide as a type of environmentally friendly and low-cost thermoelectric material has attracted extensive attention in the last few years. However, the thermoelectric performance and stability of pristine copper sulfides are poor because of the excessive hole concentration and Cu-ion migration behavior in the high temperature, which are the key reason why this material system can't become the candidate of commercial application. In this paper, carbon nanotubes (CNTs) were coated with CuO by ultrasonic spraying pyrolysis, and then waiting to be compounded with Cu 1.8 S material. A series of copper sulfide-based composites were produced by combining with solid-state reaction (SSR) and spark plasma sintering (SPS) technique. The effect of dispersing CNT/CuO on optimizing thermoelectric properties of copper sulfide was investigated in detail in the temperature range from 323 K to 773 K. Carrier concentration of copper sulfides was tuned by carefully regulating Cu vacancies, resulting in the significantly improved Seebeck coefficient. Meanwhile, the thermal conductivity was drastically decreased owing to the introduced pores and weakened contribution from electrical conductivity. A maximum thermoelectric figure of merit (ZT) value of 1.05 was obtained at 773 K for the copper sulfide-based bulk composite, namely Cu 1.8 S-5 wt. % CNT/CuO, which was twice as higher as the pristine Cu 1.8 S specimen. This bulk composite also exhibits a relatively stable thermoelectric performance in the cycling test. • Copper sulfide and CNT/CuO composites were fabricated by SSR and SPS. • The S values of the composites were enhanced from 102 μVK-1–206 μVK-1 compared to the pristine sample. • A peak ZT reached 1.05 at 773 K for the Cu1.8S bulk sample with 5 wt% CNT/CuO. • The stability of composites was improved compared to the pristine sample. [ABSTRACT FROM AUTHOR]

Both single crystal and polycrystalline SnSe have been widely investigated due to their superior thermoelectric properties in the medium temperature range. Due to its poor mechanical properties and complex and time-consuming synthesis process, single crystal SnSe is difficult to apply commercially. In this work, n-type polycrystalline SnSe with high thermoelectric properties was fabricated by LaCl 3 doping via the melting method combined with the spark plasma sintering (SPS) technique. Surprisingly, it was found that the different doping processes affect the electrical behavior of LaCl 3 -doped polycrystalline SnSe. The sample of LaCl 3 -doped SnSe was p-type when ball milling and the SPS technique were employed in our previous work, and the sample was n-type when the melting method and SPS were employed in this work. The doping mechanism was investigated in detail in this work. [Display omitted] • LaCl 3 -doped SnSe was fabricated via the melting method and SPS. • The dopant atom position in SnSe lattice depends on the synthesis process. • Power factor of 562 ​μWm−1K−2 ​at 773 ​K was achieved in n-type polycrystalline SnSe. • The highest ZT of 0.85 ​at 773 ​K was achieved in SnSe 0.95 +1 ​wt% LaCl 3 at 773 ​K. [ABSTRACT FROM AUTHOR]

[Display omitted] • Temperature gradient cooling technique can suppress the intrinsic Ge vacancies. • Bi-Sb co-doping can suppress intrinsic Ge vacancies and realize band convergence. • Pristine GeTe shows a fairly high ZT of 1.36 at 700 K. • An enhanced maximum ZT of 1.9 at 753 K is achieved in Ge 0.91 Bi 0.06 Sb 0.03 Te. GeTe-based alloys have drawn increasing attention because of the excellent thermoelectric (TE) performance and potential applications in mid-temperature range. Although reducing carrier concentration by aliovalent doping plays an important role in maximizing the TE performance of GeTe alloys, modulating the intrinsic Ge vacancies is also indispensable. In this work, the intrinsic Ge vacancies of GeTe crystals were suppressed by the synthesis process of temperature gradient cooling technique (TGCT) and Bi-Sb co-doping. The later aliovalent doping also derives a facilitated band convergence, enhanced density-of-state effective mass, and maintained carrier mobility with optimized carrier concentration, along with enhanced phonon scattering from the fluctuations of mass and strain. Benefiting from enhanced electrical properties and reduced thermal conductivity, Ge 0.91 Bi 0.06 Sb 0.03 Te achieved a maximum ZT of 1.9 at 753 K, together with a comparable average ZT of 1.14 at 300–773 K. The results reveal the potential of the TGCT fabrication and Bi-Sb co-doping on enhancing TE performance of GeTe-based alloys with a strengthened suppression of Ge vacancies. [ABSTRACT FROM AUTHOR]

The decrease in lattice thermal conductivity is one of the most effective methods for enhancing thermoelectric properties. Achieving lattice thermal conductivity close to the theoretical limit is extremely difficult while maintaining an impressive power factor. By introducing ultrafine bismuth sulfide nanograins, strong phonon scattering was generated by associated multiscale lattice defects to further gain a low lattice thermal conductivity of 0.244 W/m/K approaching Clarke's limitation of 0.242 W/m/K. Simultaneously, the electrical conductivity was increased by S diffusion and suppression of the antisite defects, and a high power factor was maintained to produce an improved ZT peak of 1.2 at 473 K for the Bi 2 Te 2.7 Se 0.3 + 1 wt % Bi 2 S 3 #2 sample. This sample was used to fabricate a small device with a p-leg, and the direct conversion efficiency reached 4.39%. Inverse changes in hardness and Young's modulus in conjunction with Bi 2 S 3 content are first reported in thermoelectric materials, which has potential assistance in synchronously improving their mechanical and thermoelectric properties. [Display omitted] [ABSTRACT FROM AUTHOR]

• PbBr 2 doped n -type polycrystalline SnSe that forms multi-nanoprecipitates. • The carrier concentration increased to 1.79 × 1019 cm−3 at room temperature. • The thermal conductivity decreased to 0.32 Wm−1K−1 at 773 K. • A ZT peak reaches 1.1 at 773 K along the parallel to SPS pressure direction. Both p - and n -type SnSe single crystals have been reported to possess high thermoelectric performances, thus highlighting the possibility for commercialization. Polycrystalline SnSe that has better mechanical properties however possesses inferior thermoelectric properties compared to single crystal SnSe. In this work, n -type polycrystalline SnSe 0.95 + x wt% PbBr 2 (x = 0, 0.5, 1, and 1.5) samples were synthesized by combining mechanical alloying and spark plasma sintering technology. The effects of PbBr 2 doping on thermoelectric performance of SnSe were studied in detail. The results show that the carrier concentration was dramatically increased from 2.51 × 1017 cm−3 in pure SnSe 0.95 to 1.79 × 1019 cm−3 in SnSe 0.95 + 1.5 wt% PbBr 2 , further resulting in an enhanced electrical conductivity. Multi-nanoprecipitates are present in the samples, including SnO, SnPb and SnBr x O y , which possibly affect the Seebeck coefficient and the lattice thermal conductivity. A peak ZT value of 1.1 was obtained at 773 K for the SnSe 0.95 + 1.0 wt% PbBr 2 sample. This work highlights that PbBr 2 is an effective dopant to improve the TE performance of n -type polycrystalline SnSe. [ABSTRACT FROM AUTHOR]

Bi 2 S 3 is considered a potential thermoelectric material owing to its non-toxic and earth-abundant components and intrinsically low thermal conductivity. However, owing to its low electrical conductivity and the coupling relationship between the electric transport properties and thermal transport properties, achieving a high ZT value for polycrystalline Bi 2 S 3 is a major challenge. In this work, a high-valence halogen compound, NbCl 5 , was employed to enhance the thermoelectric properties of polycrystalline Bi 2 S 3 fabricated by the melting method combined with the spark plasma sintering technique. The enhanced electrical conductivity of polycrystalline Bi 2 S 3 is derived from the increased carrier concentration, which is caused by the substitution of Nb and Cl ions into Bi and S sites, respectively. A peak power factor of 363 μWm−1K‒2 was obtained for Bi 2 S 3 with 1.0 ​wt% NbCl 5 doping at 623 ​K. Finally, a maximum ZT of ~0.28, which is approximately four times higher than that of the pristine Bi 2 S 3 sample, was obtained. This work proves that NbCl 5 is an effective n-type dopant for the Bi 2 S 3 system, and indicates that high thermoelectric performance can be realized for Bi 2 S 3 with environmentally friendly and low-cost elements. [Display omitted] • The Bi 2 S 3 specimens were fabricated via melting method followed by SPS. • The NbCl 5 as donor dopant is effectively improve the electric conductivity of Bi 2 S 3. • A peak ZT value of 0.28 is obtained for Bi 2 S 3 doped with 1.0 ​wt% NbCl 5 at 623 ​K. [ABSTRACT FROM AUTHOR]