p-Type and n-type thermoelectric semiconductor materials with compatible performance are key components for thermoelectric devices. Great improvement in thermoelectric performance has been achieved in p-type PbTe, whereas the n-type counterpart still shows much inferior thermoelectric performance compared to that of the p-type PbTe. This inspires many strategies focused on advancing n-type PbTe thermoelectrics. Herein, not only effective mass engineering, resonance states, point defects, and nanostructures but also newly developed concepts including dynamic doping for stabilizing the optimal carrier concentration and introducing dislocations for reducing lattice thermal conductivity are summarized. In addition, the synergistic effects for further enhancing the thermoelectric performance are outlined, together with a discussion and outlook for boosting the advancement in n-type PbTe thermoelectric materials. Strategies discussed here are expected to be applicable to other thermoelectric materials.

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Most achievements on remarkable thermoelectric performance have been made in the intermediate-temperature p-type PbTe. However, the n-type PbTe exhibits a relatively poor figure of merit ZT, which is urgently expected to be enhanced and compatible with the p-type counterpart. Here, we report that the introduction of excessive Pb can effectively eliminate cation vacancies in the n-type Pb1+xTe−0.4%I, leading to a considerable improvement of carrier mobility μ. Moreover, further Ge doping induces a large enhancement of thermoelectric properties due to the combined effect of improved electrical transport properties and increased phonon scattering in the n-type Pb1.01Te−0.4%I−y%Ge. The Ge doping not only contributes to the increase of the Seebeck coefficient owing to the increased effective mass m∗, but also gives rise to the dramatic decrease of lattice thermal conductivity due to the strengthened point defects scattering. As a result, a tremendous enhancement of the ZT value at 723 K reaches ∼1.31 of Pb1.01Te−0.4%I−3%Ge. Particularly, the average ZTave value of ∼0.87 and calculated conversion efficiency η∼13.5% is achieved by Ge doping in a wide temperature range from 323 to 823 K. The present findings demonstrate the great potential in the n-type Pb1.01Te−0.4%I−y%Ge through a synergistic tuning of carrier mobility, effective mass, and point defects engineering strategy.

Texturization tuning is of crucial significance for designing and developing high-performance thermoelectric materials and devices. Here, we report for the first time that a strong texturization effect induces an in-plane high-performance thermoelectric and an out-of-plane low lattice thermal conductivity in Sb-substituted misfit-layered (SnS)1.2(TiS2)2 alloys. In the in-plane direction, the oriented texture promotes a high carrier mobility, contributing to the maximization of the power factor (∼0.90 mW K–2 m–1). Moreover, the in-plane lattice thermal conductivity dramatically reduces deriving from the point defects due to the Sb substitution and weakened transverse sound velocity owing to the softening of bonding, ultimately leading to one of the highest thermoelectric performances ever reported among misfit-layered chalcogenides. In particular, in the out-of-plane direction, the texturization triggers the lowest lattice thermal conductivity (∼0.39 W K–1 m–1), exceeding the theoretical limit of the Debye–Cahill model, which provides a precious opportunity to investigate this real Sb-substituted (SnS)1.2(TiS2)2 material. The present finding in misfit-layered chalcogenides provides a novel strategy for manipulating thermoelectrics via texturization engineering.

The enhancement of thermoelectric performance is directly triggered by a Co- and Cu-substituted alloying effect in misfit-layered (SnS)1.2(TiS2)2.

Numerous endeavors have been made to advance thermoelectric SnTe for potential applications. Effective strategies focus on the manipulation of transport properties, including valence band convergence, resonate state, and defect engineering. It has been demonstrated that alloying trivalent Bi or chalcogenide SnSe alone in SnTe can trigger an inherent enhancement of thermoelectric performance. However, what the critical role in the transport valence band co-doping Bi and Se in SnTe plays is still unclear. Particularly, fully evaluating the effect of band convergence on the carrier concentration-dependent weighted mobility, which dominates the electronic performance, is primary and essential for designing excellent thermoelectric materials. Here, we report that Bi doping in SnTe–SnSe alloys can derive a distinct decrease in the energy offset between the two valence bands, thus improving the density-of-state effective mass by only slightly deteriorating the mobility. The well-established theoretical model reveals that the Bi-doping-induced band convergence and the optimized carrier concentration actually enhance the weighted mobility, contributing to the improvement of electronic performance. Moreover, the Debye–Callaway model demonstrates the origin of the reduced lattice thermal conductivity. The present results confirm the potential of transport engineering in promoting thermoelectric performance.

The fundamental challenge for enhancing the thermoelectric performance of n-type PbTe to match p-type counterparts is to eliminate the Pb vacancy and reduce the lattice thermal conductivity. The Cu atom has shown the ability to fill the cationic vacancy, triggering improved mobility. However, the relatively higher solubility of Cu2Te limits the interface density in the n-type PbTe matrix, leading to a higher lattice thermal conductivity. In particular, a quantitative relationship between the precipitate scattering and the reduction of lattice thermal conductivity in the n-type PbTe with low solubility of Cu2Te alloys still remains unclear. In this work, trivalent Sb atoms are introduced, aiming at decreasing the solubility of Cu in PbTe for improving the precipitate volumetric density and ensuring n-type degenerate conduction. Benefiting from the multiscale hierarchical microstructures by Sb and Cu codoping, the lattice thermal conductivity is considerably decreased to 0.38 W m–1 K–1. The Debye–Callaway model quantifies the contribution from point defects and nano/microscale precipitates. Moreover, the mobility increases from 228 to 948 cm2 V–1 s–1 because of the elimination of cationic vacancies. Consequently, a high quality factor is obtained, enabling a superior peak figure of merit ZT of ∼1.32 in n-type Pb0.975Sb0.025Te by alloying with only ∼1.2% Cu2Te. The present finding demonstrates the significant role of low-solubility Cu2Te in advancing thermoelectrics in n-type PbTe.

Small-bandwidth n-type PbTe–MnTe alloys effectively modify the valley shape, while it also inevitably aggravates the deterioration of carrier mobility as nonpolar phonons dominate the scattering. It is found that a trace amount of Cu doping can alleviate the compromises among thermoelectric parameters, thereby significantly optimizing the electrical-transport performance near room temperature of n-type PbTe–MnTe alloys. The single-Kane model reveals that the physical origin of performance improvement lies in the carrier mobility enhancement and self-optimization of carrier concentration. The Debye–Callaway model further quantifies the contribution of copper defect scattering to the lattice thermal conductivity. Notably, the high thermoelectric quality factor obtained in this work rationalizes their superior properties and reveals immense potential for achieving higher zT. Herein, an extremely high zT of ∼0.52 at room temperature and a maximum zTmax of ∼1.2 at 823 K are achieved in 0.3% Cu-intercalated n-type PbTe–MnTe. The mechanism in balancing compromise elaborated in principle contributes to an improvement of thermoelectric properties of the n-type PbTe alloys in a broad temperature range.