Band Convergence Research Articles

Band Engineering Through Pb-Doping of Nanocrystal Building Blocks to Enhance Thermoelectric Performance in Cu3SbSe4.

Developing cost-effective and high-performance thermoelectric (TE) materials to assemble efficient TE devices presents a multitude of challenges and opportunities. Cu3SbSe4 is a promising p-type TE material based on relatively earth abundant elements. However, the challenge lies in its poor electrical conductivity. Herein, an efficient and scalable solution-based approach is developed to synthesize high-quality Cu3SbSe4 nanocrystals doped with Pb at the Sb site. After ligand displacement and annealing treatments, the dried powders are consolidated into dense pellets, and their TE properties are investigated. Pb doping effectively increases the charge carrier concentration, resulting in a significant increase in electrical conductivity, while the Seebeck coefficients remain consistently high. The calculated band structure shows that Pb doping induces band convergence, thereby increasing the effective mass. Furthermore, the large ionic radius of Pb2+ results in the generation of additional point and plane defects and interphases, dramatically enhancing phonon scattering, which significantly decreases the lattice thermal conductivity at high temperatures. Overall, a maximum figure of merit (zTmax) ≈ 0.85 at 653 K is obtained in Cu3Sb0.97Pb0.03Se4. This represents a 1.6-fold increase compared to the undoped sample and exceeds most doped Cu3SbSe4-based materials produced by solid-state, demonstrating advantages of versatility and cost-effectiveness using a solution-based technology.

Enhanced thermoelectric performance and mechanical strength in GeTe enable power generation and cooling

AbstractFinding a real thermoelectric (TE) material that excels in various aspects of TE performance, mechanical properties, TE power generation, and cooling is challenging for its commercialization. Herein, we report a novel multifunctional Ge0.78Cd0.06Pb0.1Sb0.06Te material with excellent TE performance and mechanical strength, which is utilized to construct candidate TE power generation and cooling devices near room temperature. Specifically, the effectiveness of band convergence, combined with optimized carrier concentration and electronic quality factor, distinctly boosts the Seebeck coefficient, thus greatly improving the power factor. Advanced electron microscopy observation indicates that complex multi‐scale hierarchical structures and strain field distributions lead to ultra‐low lattice thermal conductivity, and also effectively enhance mechanical properties. High ZT ~ 0.6 at 303 K, average ZTave ~ 1.18 from 303 to 553 K, and Vickers hardness of ~200 Hv in Ge0.78Cd0.06Pb0.1Sb0.06Te are obtained synchronously. Particularly, a 7‐pair TE cooling device with a maximum ΔT of ~45.9 K at Th = 328 K, and a conversion efficiency of ~5.2% at Th = 553 K is achieved in a single‐leg device. The present findings demonstrate a unique approach to developing superior multifunctional GeTe‐based alloys, opening up a promising avenue for commercial applications.image

Functionally separated electronic band engineering via multi-element doping plus high-density defects advances board-temperature-range thermoelectric performance in GeTe

GeTe has attracted widespread attention as an ideal mid-temperature thermoelectric (TE) material, but its peak performance within a narrow mid-temperature range limits the conversion efficiency improvement of future TE devices. Here, to achieve the overall enhancement of GeTe over a broad temperature range, especially near room temperature, we demonstrate the functionally separated electronic band engineering strategy (resonance energy levels and band convergence) coupling the construction of high-density defects by designing multi-element SnSe-In-Sb co-doping. Fundamentally, to distinguish the functions of selected elements, it was found that SnSe alloying mainly promotes the band convergence of GeTe in elevated temperatures, In doping can create the resonance energy level for enhancing the TE performance near room temperature, and Sb can optimize symmetry and the overall carrier concentration, thereby jointly improving the effective mass and Seebeck coefficient. Moreover, the construction of various phonon scattering centers including high-density Ge micro/nano-precipitates, van der Waals gaps, dislocations, and strong stress fields, strongly inhibits phonon transport. Benefiting from these synergistic effects, a peak ZT of ∼ 2.0 at 653 K, ZTave of ∼ 1.2 in the range from 303 to 803 K, and Vickers microhardness of ∼ 234 Hv are obtained in (Ge0.91In0.01Sb0.08Te)0.98(SnSe)0.02 sample. This study demonstrates a promising strategy to optimize thermoelectric performance by selectively co-doping functionally separated elements for developing high-performance TE materials.

High power factor and ultra-low lattice thermal conductivity in Sn1−xWxTe alloys via interstitial defects modulation

SnTe, a potential substitute for excellent medium-temperature thermoelectric (TE) material PbTe, has recently attracted much attention in TE energy conversion. Herein, we demonstrate a rare and effective strategy to synergistically optimize the electrical and thermal transport properties of SnTe by introducing Tungsten(W) interstitial defects. Concretely, the formation energy of intrinsic Sn vacancy defects is reduced by introducing W-interstitial defects, thus increasing the hole carrier concentration and overall electrical conductivity. Meanwhile, the increase of band degeneracy (band flattening and valence band convergence) markedly enhances the Seebeck coefficient, which exhibits the high average power factor of ∼17.79 μWcm−1K−2. Moreover, the lattice thermal conductivity is significantly reduced to 0.46 Wm−1K−1, which arises from the enhancement of phonon scattering caused by various processes including dislocations, crystal defects and multiscale nanoprecipitation. These combined effects lead to a maximum ZT value of ∼0.79 at 823 K for Sn0.97W0.03Te, especially the average ZT value remarkably increased to 0.26. Conclusively, unlike conventional work to optimize electrical transport performance (reducing hole carrier concentration), this work provides an innovative strategy to significantly improve the electrical properties of SnTe through the modulation of W-interstitial defects.

Multifunctional GeMnTe2 Synergistically Optimizes Thermoelectric Properties of SnTe-In2Te3 Alloys.

SnTe-In2Te3 alloys ensure excellent electrical properties in the whole temperature region due to the resonant level. Nevertheless, temperature-sensitive resonance states and single phonon scattering restrict further improvement of thermoelectric performance. Consequently, it is anticipated that additional electrically independent scattering sources should be introduced to impede phonon transport. Here, the SnTe-In2Te3-GeMnTe2 alloy is prepared by further solidifying cubic GeMnTe2, which demonstrates multiple modulation effects. The highly redissolved Mn2+ promotes the valence band convergence, enhances the Seebeck coefficient at higher temperature, and balances the possible weakened resonance level effect at higher carrier concentrations, and a high average power factor (1.94 mW m-1 K-2) is realized over the entire temperature range. Additionally, compensatory vacancies, substitutions, and Ge/Mn precipitates are easily constructed with GeMnTe2 alloying, leading to a further reduction in lattice thermal conductivity, which reaches κl ∼ 0.6 W m-1 K-1 at 850 K. Ultimately, a high peak zT of ∼1.25 (850 K) and a zTave of 0.72 (300-850 K) are realized in (SnTe)2.91(In2Te3)0.03(Ge0.5Mn0.5Te)1.2, and the maximum thermoelectric conversion efficiency of ∼2.8% (ΔT ∼ 450 K) is achieved. The present results indicate multiple effects of GeMnTe2 in enhancing the thermoelectric performance of SnTe-In2Te3 alloys.

Dopant induced band convergence leading to high thermoelectric power factor in Mg2Sn

Band convergence is a common technique for enhancing the power factor of thermoelectric (TE) materials. This is usually achieved by solid solution formation in compounds having specific electronic band features. In this work, we show that a similar band convergence effect can be achieved in Mg2Sn by doping with small amounts of Bi. To identify this effect and the possible reason behind it, a detailed investigation of the electronic band structure (EBS) has been carried out using a recently developed multi-band refinement technique (MBRT). Nominal compositions of Mg2.2Sn1-xBix (x = 0,0.005, 0.01, 0.0125, 0.015, 0.02) have been synthesized by induction melting followed by compaction using uniaxial hot-pressing. Measurement of Seebeck coefficient (S), electrical conductivity (σ) and Hall Coefficient (RH) have been performed between 300K–700K and the data used for multi-band refinement. Results indicate changes in the inter-band separation of conduction bands with doping content and temperature. Significantly lower inter-band separation compared to reported undoped data is found even for the lowest doped composition, resulting in both conduction bands contributing to the power factor (S2σ). Further, for the heavily doped compositions (x = 0.0125, 0.015, 0.02) band-flipping between the conduction bands has been observed. Thus, the light conduction band is found to constitute the conduction band edge in the heavily doped compositions. This is contrary to the reported EBS of undoped Mg2Sn in which the heavy conduction band has a lower energy. Also, increasing temperature results in band convergence in the heavily doped compositions. A plausible cause for the band-flipping behaviour is provided based on merging of the impurity band with the light conduction band in heavily doped Mg2Sn. The band-flipping and the subsequent band convergence results in an even higher S2σ in the heavily doped compositions. The work highlights the beneficial influence of Bi doping on the TE properties of Mg2Sn and opens the possibility of utilizing dopants for achieving band convergence in TE materials.

Rattling-like behavior and band convergence induced ultra-low lattice thermal conductivity in MgAl2Te4 monolayer

Inspired by the excellent stability exhibited by experimentally synthesized two-dimensional (2D) MoSi2N4 layered material, the thermal and electronic transport, and thermoelectric (TE) properties of MgAl2Te4 monolayer are systematically investigated using the First-principles calculations and Boltzmann transport theory. The mechanical stability, dynamic stability, and thermal stability (900 K) of the MgAl2Te4 monolayer are demonstrated, respectively. The MgAl2Te4 monolayer exhibits a bandgap of 1.35 eV using the HSE06 functional in combination with spin-orbit coupling (SOC) effect. Band convergence in the valence band is favorable to improve the thermoelectric properties. The rattling thermal damping effect caused by the weak bonding of MgTe bonds in MgAl2Te4 monolayer leads to ultra-low lattice thermal conductivity (0.95/0.38 W/(m·K)@300 K along the x-/y-direction), which is further demonstrated by the phonon group velocities, phonon relaxation time, Grüneisen parameters, and scattering mechanisms. The optimal zT of 3.28 at 900 K is achieved for the p-type MgAl2Te4 monolayer, showing the great promising prospect for the excellent p-type thermoelectric material. Our current work not only reveals the underlying mechanisms responsible for the excellent TE properties, but also elaborates on the promising thermoelectric application of MgAl2Te4 monolayer material at high temperature.

Weakening the spin–orbital coupling for band convergence

Band convergence is a favorable strategy that is utilized to improve the thermoelectric performance in experiment, whereas a theoretical guidance for this purposive design is rare. With high-level first-principles treatment of electronic and transport properties in the emerging ABX (A = Ca, Sr, Ba; B = Cu, Ag; X = P, As, Sb) Zintl systems, a principled scheme via weakening the spin–orbital coupling is proposed based on symmetry and orbital analysis to promote the band convergence. This given rule is numerically confirmed in BaAgX alloys. Despite the intensified intervalley electron–phonon scattering, the alloying of BaAgP in BaAgSb prominently triggers the band convergence and contributes to much larger density of state effective mass, which eventually results in a ∼40% improvement in zT values. This work offers an applicable principle for designing band convergence, which also broads the compositions of thermoelectrics to light and earth-abundant elements.

Dilute Sc/Y doping in SnTe for efficient charge transport modulation and high thermoelectric performance

As a highly potential environmental-friendly medium-temperature thermoelectric material, pure SnTe exhibits relatively poor performance due to its intrinsic high carrier concentration and large energy offset between the two valence bands. In the present work, dilute Sc/Y doping is innovatively adopted to synergistically decrease carrier concentration and achieve strong band convergence. The Hall measurement results indicate that 3 % Y doping realizes the lowest carrier concentration of 2.6 × 1019 cm−3 in SnTe. Sc and Y have similar effects in promoting band convergence, with their effects second only to toxic Hg elements at the same doping concentration. The effective decoupling of electrical and thermal transport parameters results in a high average ZT of 0.453 for Sn0.975Sc0.025Te sample, which is 103 % higher than that of pure SnTe. In addition, with Li2Te alloying to regulate carrier concentration, high-performance temperature range could be adjusted, which is more conducive to dealing with different temperature scenarios. The role of Sc/Y doping disclosed in this work provides more options for further improving the performance of SnTe-based materials.

Enhancement on thermoelectric performance by Ti doping and vacancies

Due to the exceptionally low lattice thermal conductivity, AgSbTe2 has emerged as a promising thermoelectric material. However, unlike other IV-VI compounds, most reported AgSbTe2 samples exhibit relatively poor electrical performance due to low carrier concentration. Herein, an unusually strategy of introducing dopants and vacancies on the same site of Sb is adopted, which significantly improves the electrical performance of AgSbTe2. It is found that Ti doping on Sb site can increase the carrier concentration and promote band convergence, based on which the introduction of Sb vacancy further enlarges the carrier concentration to approach the optimal value without affecting the carrier mobility. Consequently, an excellent average power factor of 1.4 mW m−1K−2 is achieved in AgSb0.94 Ti0.05Te2 from 323 K to 623 K. Combining with reduced thermal conductivity due to strengthened phonon scattering induced by the abundant lattice defects, a peak zT of 1.8 and a high average zT of 1.3 are attained. These results provide some new insights for improving the thermoelectric performance of AgSbTe2 based compounds.

Two-step phase manipulation by tailoring chemical bonds results in high-performance GeSe thermoelectrics

In thermoelectrics, phase engineering serves a crucial function in determining the power factor by affecting the band degeneracy. However, for low-symmetry compounds, the mainstream one-step phase manipulation strategy, depending solely on the valley or orbital degeneracy, is inadequate to attain a high density-of-states effective mass and exceptional zT. Here, we employ a distinctive two-step phase manipulation strategy through stepwise tailoring chemical bonds in GeSe. Initially, we amplify the valley degeneracy via CdTe alloying, which elevates the crystal symmetry from a covalently bonded orthorhombic to a metavalently bonded rhombohedral phase by significantly suppressing the Peierls distortion. Subsequently, we incorporate Pb to trigger the convergence of multivalence bands and further enhance the density-of-states effective mass by moderately restraining the Peierls distortion. Additionally, the atypical metavalent bonding in rhombohedral GeSe enables a high Ge vacancy concentration and a small band effective mass, leading to increased carrier concentration and mobility. This weak chemical bond along with strong lattice anharmonicity also reduces lattice thermal conductivity. Consequently, this unique property ensemble contributes to an outstanding zT of 0.9 at 773 K for Ge0.80Pb0.20Se(CdTe)0.25. This work underscores the pivotal role of the two-step phase manipulation by stepwise tailoring of chemical bonds in improving the thermoelectric performance of p-bonded chalcogenides.

Realizing ultrahigh room-temperature seebeck coefficient and thermoelectric properties in SnTe-based alloys through carrier modulation and band convergence

Seebeck coefficient is a crucial parameter in the field of thermoelectricity as it directly impacts the output power of thermoelectric devices. Intrinsic SnTe thermoelectrics exhibit excellent electrical conductivity but suffer from its low Seebeck coefficient, significantly impeding the advancement of the performance in both materials and devices. Herein, we focus on improving the Seebeck coefficient to favor the output voltage and power of SnTe thermoelectrics. Through a stepwise optimization strategy involving carrier concentration modulation and energy band convergence, we have substantially improved the performance of p-type SnTe thermoelectrics and enhanced the Seebeck coefficient across the entire temperature range. An ultrahigh Seebeck coefficient exceeding 103 μV K−1 at ambient temperature, a highest ZT value of 1.3 at 823 K, and a maximum ZTave of ∼ 0.7 among 300–823 K were obtained in the Sn0.82Mn0.18Bi0.03Te0.91I0.09 sample. Our study provides a universal strategy for advancing SnTe-based thermoelectrics and enhancing the power generation performance, which can be well broadened and implemented in various thermoelectric systems.

Experimental verification of band convergence in Sr and Na codoped PbTe

Experimental verification of band convergence in Sr and Na codoped PbTe

Achieving Ultralow Lattice Thermal Conductivity and High Thermoelectric Performance in SnTe by Alloying with MnSb2Se4.

The manipulation of defect chemistry is crucial in the design of high-performance thermoelectric materials. Studies have demonstrated that alloying compounds within the I-V-VI2 family, such as AgSbTe2, NaSbTe2, etc., can effectively enhance the thermoelectric performance of SnTe by controlling the hole concentration and reducing the lattice thermal conductivity. In this paper, samples of SnTe alloyed with MnSb2Se4 were prepared, and the microstructure, electrical properties, and thermal properties were thoroughly investigated. Based on SEM and TEM analysis, it was observed that MnSb2Se4 can dissolve into SnTe during the preparation of the samples, which leads to the formation of various secondary phases with different compositions and point defects. Consequently, the lattice thermal conductivity is reduced to 0.44 W m-1 K-1 at 800 K, approaching the amorphous limit. Furthermore, the diffusion of the Mn and Sb elements leads to a significant improvement in the Seebeck coefficient through valence band convergence. The vacancy concentration in SnTe can also be modulated by alloying with MnSb2Se4. The findings indicated that MnSb2Se4 alloying can enhance the thermoelectric performance of SnTe through increasing the vacancy concentration, promoting valence band convergence, and introducing secondary phases. Consequently, a ZT value of 1.36 at 800 K for Sn1.03Te-5%MnSb2Se4 can be achieved.

Band engineering enhances thermoelectric performance of Ag-doped Sn0.98Se

Ag doping can effectively increase the carrier concentration of p-type SnSe polycrystalline, thereby enhancing the thermoelectric (TE) performance. However, the key role of the transport valence band in Ag-doped SnSe remains unclear. Particularly, understanding the influence of evaluating the optimal balance between band convergence and carrier mobility on weighted mobility is a primary consideration in designing high-performance TE materials. Here, we strongly confirm through theoretical and experimental evidence that Ag-doped Sn0.98Se can promote the evolution of valence bands and achieve band convergence and density of states distortion. The significantly increased carrier concentration and effective mass result in a dramatic increase in weighted mobility, which favors the achievement of superior power factors. Furthermore, the Debye model reveals the reasons for the evolution of lattice thermal conductivity. Eventually, a superior average power factor and average zT value are obtained in the Ag-doped samples in both directions over the entire test temperature range. This strategy of improving TE performance through band engineering provides an effective way to advance TEs.

Suppression of intervalley scattering and enhanced phonon anharmonic interactions in 2D Bi2TeSe2: Crystal-field symmetry and band convergence

The electron-phonon (el-ph) and phonon-phonon interactions play a key role in determining electronic and thermal transport properties, respectively, in promising two-dimensional (2D) semiconductor devices. In this study, we investigated el-ph interactions using Wannier-Fourier interpolation method and renormalized phonon scattering considering finite-temperature effects in Bi2TeSe2 monolayer. The results show that the optical phonon modes dominate the carrier scattering, where level repulsion induced by crystal field splitting and spin-orbit coupling (SOC) effect effectively suppresses intervalley scattering, leading to high hole mobility. Moreover, the strong anharmonicity in Bi2TeSe2 monolayer results in the temperature-dependent softening of its optical phonons, along with a corresponding variation in interatomic force constants (IFCs). As a result, the lattice thermal conductivity is remarkably low and exhibits weak temperature dependence. Finally, the predicted dimensionless thermoelectric figure of merit exceeds unity in the range of 200–800 K, indicating the potential of Bi2TeSe2 monolayer for thermoelectric applications. This work provides new insights into the elimination of intervalley scattering by crystal field splitting and SOC effects, and paves the way for the evaluation of thermoelectric properties of materials with complex scattering mechanisms and strong anharmonicity.

The origin of shifted fermi level and improved thermoelectric performance of monolayer BiCuSeO under pressures

The layered BiCuSeO has been widely investigated because of high thermoelectric (TE) performance. However, there is few reports about the TE property of two-dimensional (2D) BiCuSeO so far. In this work, it is found that the Fermi level passes through the conduction band of [Bi2O2]2+ layer and the valence band of [Cu2Se2]2- layer simultaneously. Therefore, there is no band gap appeared for monolayer BiCuSeO, which would lead to very poor TE performance. First-principles calculation shows that negative hydrostatic pressure could weaken the intra-layer bonding and enhance the inter-layer coupling. Thus, the Fermi level would gradually get out of conduction and valence bands along with the increased pressure. To improve the TE performance of monolayer BiCuSeO, negative hydrostatic pressures are applied and successfully increased its band gap values from 0 eV to 0.85 eV. At the same time, an obvious band convergence near conduction band minimum (CBM) is found under the −2.22 GPa pressure. Besides, the band convergence near the Fermi level under negative pressure will greatly improve the TE performance of n- and p-type monolayer BiCuSeO.

Unravelling the regulating role of strain engineering on the phonon dispersion, mechanical behavior, and electronic transport properties of pentagonal PtTe2 monolayer

Inspired by the experimental synthesis of PdSe2 monolayer with a novel buckling configuration, the mechanical property, phonon dispersion curve, electronic structure, and carrier mobility of anisotropic pentagonal PtTe2 monolayer under strain engineering are systematically investigated by first-principles calculations and deformation potential (DP) theory. Ab initio molecular dynamics (AIMD) simulations show that the pentagonal PtTe2 monolayer is thermally stable at 300 and 600 K. Further phonon dispersion investigation verifies the dynamic stability of pentagonal PtTe2 monolayer under tensile strain, as evidenced by the absence of imaginary frequency. When subjected to tensile strains ranging from 2% to 4% in uniaxial (a- and b-direction) and biaxial directions, the mechanical properties and electronic band structures of pentagonal PtTe2 monolayer exhibit significant changes, leading to the electronic band convergence and decreasing bandgap. The effective mass, elastic constant, deformation potential, and carrier mobility also vary considerably under tensile strains, and a high hole mobility of 3618.51 cm2/V·s is discovered along the a-direction with 3% strain applied in the y-axis. Specifically, the hole mobility of pentagonal PtTe2 monolayer shows large anisotropy ratio, reaching up to 13.99 under 2% tensile strain in the y-axis. Our current work not only unravels the fundamental understanding of the anisotropic mechanical properties, phonon dispersion and electronic transport properties of pentagonal PtTe2 monolayer under strain engineering, but also provides theoretical guidance for applying strain engineering to tune the unique physical properties of two-dimensional materials with pentagonal configurations.

Surface Chemistry and Band Engineering in AgSbSe2: Toward High Thermoelectric Performance.

AgSbSe2 is a promising thermoelectric (TE) p-type material for applications in the middle-temperature range. AgSbSe2 is characterized by relatively low thermal conductivities and high Seebeck coefficients, but its main limitation is moderate electrical conductivity. Herein, we detail an efficient and scalable hot-injection synthesis route to produce AgSbSe2 nanocrystals (NCs). To increase the carrier concentration and improve the electrical conductivity, these NCs are doped with Sn2+ on Sb3+ sites. Upon processing, the Sn2+ chemical state is conserved using a reducing NaBH4 solution to displace the organic ligand and anneal the material under a forming gas flow. The TE properties of the dense materials obtained from the consolidation of the NCs using a hot pressing are then characterized. The presence of Sn2+ ions replacing Sb3+ significantly increases the charge carrier concentration and, consequently, the electrical conductivity. Opportunely, the measured Seebeck coefficient varied within a small range upon Sn doping. The excellent performance obtained when Sn2+ ions are prevented from oxidation is rationalized by modeling the system. Calculated band structures disclosed that Sn doping induces convergence of the AgSbSe2 valence bands, accounting for an enhanced electronic effective mass. The dramatically enhanced carrier transport leads to a maximized power factor for AgSb0.98Sn0.02Se2 of 0.63 mW m-1 K-2 at 640 K. Thermally, phonon scattering is significantly enhanced in the NC-based materials, yielding an ultralow thermal conductivity of 0.3 W mK-1 at 666 K. Overall, a record-high figure of merit (zT) is obtained at 666 K for AgSb0.98Sn0.02Se2 at zT = 1.37, well above the values obtained for undoped AgSbSe2, at zT = 0.58 and state-of-art Pb- and Te-free materials, which makes AgSb0.98Sn0.02Se2 an excellent p-type candidate for medium-temperature TE applications.

Anionic regulation and valence band convergence boosting the thermoelectric performance of Se-alloyed GeSb2Te4 single crystal

GeSb2Te4, a layer-structured pseudo-binary chalcogenide, is a promising thermoelectric material with low lattice thermal conductivity ensured by the van de Waals gap. However, its excessive hole concentration leads to low Seebeck coefficient and limited thermoelectric performance. Herein, GeSb2(Te1-xSex)4 (x = 0, 0.05, 0.07, 0.1, and 0.15) single crystals were grown via Bridgman method for thermoelectric performance investigation, with single crystals to utilize the anisotropic low lattice thermal conductivity, and Se-alloying as the strategy to optimize the thermoelectric performance. It was found that Se alloying increases the Seebeck coefficients, deriving from the reduced carrier concentrations due to the enlarged formation energy of intrinsic GeSb(A1), GeSb(A2), and VGe(A2) defects, as well as the simultaneous enhancement of density-of-states effective mass from a facilitated valence band convergence. Besides, Se-alloying also contributes to the reduction of the lattice thermal conductivity. With the forementioned benefits, a high figure of merit of 1.02 is obtained at 723 K in the out-of-plane direction of the crystal sample GeSb2(Te0.9Se0.1)4, and a 74% improvement on average zT is gained. The study of anionic regulation and valence band convergence in GeSb2Te4-based single crystal provides an effective pathway for performance optimization in related layer-structured thermoelectric materials.