Thermoelectric materials allow for direct conversion between heat and electricity, offering the potential for power generation. The average dimensionless figure of merit ZT ave determines device efficiency. N-type tin selenide crystals exhibit outstanding three-dimensional charge and two-dimensional phonon transport along the out-of-plane direction, contributing to a high maximum figure of merit Z max of ~3.6 × 10 −3 per kelvin but a moderate ZT ave of ~1.1. We found an attractive high Z max of ~4.1 × 10 −3 per kelvin at 748 kelvin and a ZT ave of ~1.7 at 300 to 773 kelvin in chlorine-doped and lead-alloyed tin selenide crystals by phonon-electron decoupling. The chlorine-induced low deformation potential improved the carrier mobility. The lead-induced mass and strain fluctuations reduced the lattice thermal conductivity. Phonon-electron decoupling plays a critical role to achieve high-performance thermoelectrics.

Entropy engineering is one of the powerful approaches to suppress phase transitions.

Recent vast reinvestigations on GeTe, a promising thermoelectric material at medium temperature, have triggered enormous enthusiasm in the thermoelectric community again. Intrinsically, GeTe, as a p-type semiconductor, possesses plenty of Ge vacancies, resulting in extremely high carrier concentration. Meanwhile, because of the vast off-stoichiometric Ge, both concomitant Ge precipitates and Ge vacancies will influence the electrical and thermal transport properties caused by phonons and carriers scattering. Herein, we report one effective way to optimize the thermoelectric performance of GeTe through manipulating Ge vacancies and Ge precipitates via successive continuous steps. First, the optimization of carrier concentration through Bi counter-doping led to an optimum carrier concentration of ∼2.79 × 10 20 cm −3 . Second, the Ge phase aggregation was successfully suppressed by heat treatment, which enhanced the electrical properties due to improved carrier mobility. Additionally, the Ge precipitates were uniformly distributed by heat treatment, which provided all-scale phonons scattering and effectively reduced the lattice thermal conductivity. Finally, combined with the significantly increased power factor (PF) and the decreased thermal conductivity, the maximum ZT of ∼1.9 at 723 K was eventually obtained in Ge 0.94 Bi 0.06 Te just through optimizing Ge vacancies and manipulating Ge precipitates by means of heat treatment.

coefficient, σ represents electrical conductivity, T represents working temperature in Kelvin, κ ele denotes electronic thermal conductivity, and κ lat denotes lattice thermal conductivity. [4,5] Extensive efforts are devoted to decoupling these correlative parameters. [6] Electrically, the strategies of band convergence, [2] band alignment, [4,7] densityof-states (DOS) distortion, [8,9] modulation doping, [10] enhancing the symmetry of crystal [11] and quantum confinement [12] are successfully established to equilibrate the Seebeck coefficient (S) and the electrical conductivity (σ) in favor of a superior power factor (PF). [13] It is well known that the enhanced band degeneracy due to band convergence could increase the effective mass a bit without degrading the carrier mobility. And DOS distortion, which improves the band effective mass, is a feasible strategy with risks for deteriorating the carrier mobility. [14] It is clear that the optimal balance between the effective mass and the carrier mobility is beneficial for the electrical performance of TE materials. This relationship primarily depends on the weighted mobility, µW = μ H (m * /m e ) 3/2 , where μ H represents the carrier mobility, m * represents the DOS effective mass, and m e represents the unit electron mass.Thermally, intensifying the phonon scattering is considered to be an effective method to decrease the thermal conductivity (κ lat ), which is generally classified into incorporating extra phonon scattering centers [15] and seeking inherent low lattice thermal conductivity materials. [16,17] The latter representing materials might have a complex crystal structure, [1] heavy constituent elements, [18] intense lattice anharmonicity, [19] and soft chemical bonding. [20] And the extra phonon scattering sources include point defects, nanoprecipitates, grain boundaries, and so on. [21] To date, state-of-the-art TE materials, including Zintl phase, [22] half-Heusler, [23] skutterudite, [24] SiGe, [25] chalcogenides, [8,26] and Bi 2 Te 3 -based compounds, [27] etc., exhibit prominent thermoelectric performance.GeTe is proven to be an eminent mid-temperature thermoelectric material. [28,29] The well-recognized characters of GeTe are multiple valance bands, phase transition, ultrahigh carrier concentration, and high thermal conductivity, which diversify the degrees of freedom to tailor its TE performance. [30][31][32] Counter-doping using aliovalent elements, such as Bi, Sb, and In, [33,34] is a common method to achieve the optimal carrier Thermoelectric materials can achieve the direct conversion between electricity and heat, which has drawn extensive attention in recent decades. Understanding the chemical nature of band structure and microstructure is essential to boost the thermoelectric performance of given materials. Herein, CdSe alloying promotes the evolution of multiple valence bands in GeTe, resulting in the contemporaneous appearance of band convergence and density of state distortion, which benefits the sharply enhanced effective mass from ...

It is well known that the thermoelectric performance of GeTe is difficult to manipulate due to its intrinsic overhigh carrier concentration and phase transition. Herein, we achieve that electrical and...

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