Room Temperature Seebeck Coefficient Research Articles

Optimization of Thermoelectric Properties and Physical Mechanisms of Cu2Se-Based Thin Films via Heat Treatment.

Cu2Se is an attractive thermoelectric material due to its layered structure, low cost, environmental compatibility, and non-toxicity. These traits make it a promising replacement for conventional thermoelectric materials in large-scale applications. This study focuses on preparing Cu2Se flexible thin films through in situ magnetron sputtering technology while carefully optimizing key preparation parameters, and explores the physical mechanism of thermoelectric property enhancement, especially the power factor. The films are deposited onto flexible polyimide substrates. Experimental findings demonstrate that films grown at a base temperature of 200 °C exhibit favorable performance. Furthermore, annealing heat treatment effectively regulates the Cu element content in the film samples, which reduces carrier concentration and enhances the Seebeck coefficient, ultimately improving the power factor of the materials. Compared to the unannealed samples, the sample annealed at 300 °C exhibited a significant increase in room temperature Seebeck coefficient, rising from 9.13 μVK-1 to 26.73 μVK-1. Concurrently, the power factor improved from 0.33 μWcm-1K-2 to 1.43 μWcm-1K-2.

High thermoelectric performance of GeTe-MnTe alloy driven by spin degree of freedom

GeTe has been known as an excellent thermoelectrics, whereas its realistically application is limited by its structural phase transition near 700 K. Here, we show that the temperature of phase transition can be suppressed below 300 K by alloying 35% MnTe. The GeTe-MnTe alloy exhibits the much different transport properties from GeTe. Its room-temperature Seebeck coefficient is close to that of optimized GeTe, while its carrier concentration is one order higher. The increase of Seebeck coefficient of GeTe-MnTe is found to be accompanied with the decrease of magnetic susceptibility, while GeTe shows the opposite trend. By optimizing the carrier concentration with Bi doping and Bi/Sb co-doping, the peak figure of merit of GeTe-MnTe reaches 1.46 at 823 K. Our study reveals that GeTe-MnTe alloy is a novel and promising thermoelectric material.

Phase composition and thermoelectric properties of Cu–Ag–Se films with different Ag content

In this study, a series of Cu–Ag–Se films were prepared on Si (100) substrate by magnetron sputtering. The phase composition, micro-structure and thermoelectric properties were studied. The results showed that the phase composition of deposited Cu–Ag–Se films varied from β-Cu2-xSe and a small amount of CuAgSe phase to majority β-Cu2-xSe and minority CuAgSe phase, minority β-Cu2-xSe and majority CuAgSe phase, CuAgSe and a small amount of β-Cu2-xSe phase, Ag2Se and a small amount of CuAgSe +β-Cu2-xSe phase as Ag content increased from 0.4 to 17.0, 20.8, 29.5, 41.4 at.%, respectively. In the deposited Cu–Ag–Se films, the carrier concentration first decreased and then increased and the mobility displayed an opposite trend with increasing CuAgSe content (decreasing β-Cu2-xSe content). The room temperature electrical conductivity and absolute value of room temperature Seebeck coefficient gradually increased with increasing CuAgSe content for the deposited Cu–Ag–Se films. The power factor of 29.5 at.% Ag samples (CuAgSe phase films) at whole measured temperature was the highest in all samples due to high Seebeck coefficient and high electrical conductivity, resulting in the highest PF value of 2.05 mW m−1 K−2 at 62 °C. However, due to its high thermal conductivity of 10.93 W m−1K−1, the room temperature ZT value of this sample was only 0.05 even if it possessed a higher PF value. Ag2Se phase films possessed the lowest PF value due to their lower Seebeck coefficient even if they possessed higher electrical conductivity.

In Situ Synthesis of High Thermoelectric Performance Bi2Te3 Flexible Thin Films through Thermal Diffusion Engineering

Bi2Te3-based materials are promising candidates for near-room-temperature applications due to their high thermoelectric performance and low cost. Here, an innovative thermal diffusion strategy combined with magnetron sputtering and thermal evaporation methods was employed to fabricate Bi2Te3 flexible thin films (f-TFs) on a flexible polyimide substrate. An in situ synthesis of Bi2Te3 f-TFs with good crystallinity was obtained using a straightforward thermal diffusion method through diffusion of Te into a Bi precursor under low vacuum conditions (1 × 105 Pa). This method offers easy preparation, low cost, and a large-area film preparation for industrialization. The electrical conductivity increases with increasing thermal diffusion temperatures. A high room temperature carrier mobility of ~28.7 cm−2 V−1 S−1 and an electrical conductivity of ~995.6 S cm−1 can be achieved. Then, a moderate room temperature Seebeck coefficient >100 μV K−1 was obtained due to the chemical stoichiometry being close to the standard by optimizing the thermal diffusion temperature. Consequently, a maximum room temperature PF of ~11.6 μW cm−1 K−1 was observed in Bi2Te3 f-TFs prepared using a thermal diffusion temperature of 653 K. The thermal diffusion strategy applied in the thin film preparation represents an effective approach for the preparation of high thermoelectric performance Bi2Te3 f-TFs, offering a promising route for future thermoelectric applications.

Influence of Si content on thermoelectric properties of Mg2(Sn,Si) films by sputtering

Mg2(Sn,Si) films with different Si content were prepared by magnetron sputtering. The phase composition, surface and cross-sectional morphology, chemical composition and element distribution, carrier concentration, carrier mobility, electrical conductivity, Seebeck coefficient and power factor of the deposited Mg–Sn–Si films were studied. The results show that the deposited films are composed of Mg2(Sn,Si) solid solution phase and a small amount of metal Mg phase. The room temperature carrier concentration decreases and mobility increases with increasing Si content in deposited Mg–Sn–Si films, respectively. The room temperature electrical conductivity and Seebeck coefficient decreases and increases with increasing Si content, respectively. The deposited Mg2(Sn,Si) films with moderate Si content possess the maximum power factor value of 2.76 mW m−1 K−2 at 303 °C and its room temperature figure of merit reaches the highest value of 0.44. The thermal conductivity decreases with increasing Si content, indicating that the lattice distortion caused by Si doping can reduce the thermal conductivity of the deposited films.

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.

First principles investigations of the electronic, elastic, mechanical, anisotropic, optical, and thermoelectric performance of monoclinic SiGe semiconductors

Since crystal structure dictates the resultant physical properties of materials, titled physical features of the P21 monoclinic SiGe semiconductors, which are still unclear, have been revealed by density functional theory (DFT). The electronic band gap value with 0.49[Formula: see text]eV was found to be in the order of previously published cubic and hexagonal closed-packed SiGe semiconductors. Surprisingly, P21 monoclinic SiGe has a room temperature Seebeck coefficient of 1500[Formula: see text][Formula: see text]V/K which is higher than the reported data of both cubic and hexagonal SiGe alloys. Further, the mechanically stable P21 monoclinic phase of the SiGe displays a brittle mechanical character with clear elastic anisotropy has also been deduced. The P21 monoclinic phase of the SiGe can be also considered a good high-dielectric material and beneficial for practical applications of IR or UV goals due to its high refractive index.

Nanoengineering Approach toward High Power Factor Ag2Se/Se Composite Films for Flexible Thermoelectric Generators.

Herein, a flexible Ag2Se/Se composite film with a high power factor has been fabricated on a nylon membrane. The film has a high density and contains well-crystallized Ag2Se grains and embedded Se nanoinclusions, which exhibits not only excellent flexibility but also a comparably large room-temperature power factor and Seebeck coefficient of up to 2023 μW m-1 K-2 and -155 μV K-1, respectively. The high Seebeck coefficient is ascribed to the energy-filtering effect as caused by the Se/Ag2Se heterointerface. The assembled flexible thermoelectric generator (4-leg) exhibits a maximum output power of 1135 nW and a power density of up to 16.4 W m-2 when the applied temperature difference is 30 K. This work offers a feasible method to design high-performance and low-cost flexible thermoelectric generators used for wearable electronics.

The effects of Zn doping on the thermoelectric performance of Cu12Sb4S13

In this study, first-principles electronic structure calculations and Boltzmann transport theories were used to understand the thermoelectric behavior of tetrahedrites. Calculations were performed on zinc (Zn)-substituted derivatives with zinc occupying each lattice site in the parent compound Cu12Sb4S13 to study the zinc substitution mechanism and the relation between the zinc substitution site and thermoelectric performance. It was found that the most energetically favorable sites for zinc are the Cu(1) sites, and the next are the Cu(2) sites. Furthermore, the room-temperature Seebeck coefficient of the host was enhanced nearly 255 and seven times by zinc doping at Cu(1) and Cu(2) sites, respectively, owing to the decrease in carrier concentration and the increase in band effective mass, respectively. However, the electrical conductivity showed a marked decrease upon zinc doping at Cu(1) and Cu(2) sites, due to the decrease in carrier contribution and low mobility, respectively. As a result, Cu12Sb4S13 compounds substituted with zinc at Cu(1) sites have a preferable optimizing power factor at room temperature. The optimizing power factor of the host could obtain approximately eight times improvement at room temperature upon zinc substitution at Cu(1) sites.

Thermoelectric properties and Kondo transition in the pseudo‐gap metals TiNiSi and TiNiGe

AbstractMaterials with the TiNiSi structure have recently been highlighted as potential thermoelectric materials. Here we report the thermoelectric properties of TiNiX (X=Si and Ge). Both materials behave as defective metals or heavily doped degenerate semiconductors. Room temperature Seebeck coefficients are −45 μV K−1 (Si) and −20 μV K−1 (Ge) with electrical resistivities of 0.5–1 mΩ cm. The lattice thermal conductivities are 8 W m−1 K−1 (Si) and 6 W m−1 K−1 (Ge) at 360 K, which is promising in the absence of alloying. The calculated power factors and figures of merit remain small, with the largest S2/ρ=0.17 mW m−1 K−2 and peak zT=5×10−3 seen in TiNiSi near 300 K. Both compositions show Kondo behaviour at low‐temperatures, linked to the emergence of local moment magnetism, and have substantial magnetoresistance effects at 2 K. This work provides property characterisation for two members of this large class of intermetallic materials.

Self‐Healable and Stretchable PAAc/XG/Bi2Se0.3Te2.7 Hybrid Hydrogel Thermoelectric Materials

Thermoelectric power generators have attracted increasing interest in recent years owing to their great potential in wearable electronics power supply. It is noted that thermoelectric power generators are easy to damage in the dynamic service process, resulting in the formation of microcracks and performance degradation. Herein, we prepare a new hybrid hydrogel thermoelectric material PAAc/XG/Bi2Se0.3Te2.7 by an in situ polymerization method, which shows a high stretchable and self‐healable performance, as well as a good thermoelectric performance. For the sample with Bi2Se0.3Te2.7 content of 1.5 wt% (i.e., PAAc/XG/Bi2Se0.3Te2.7 (1.5 wt%)), which has a room temperature Seebeck coefficient of −0.45 mV K−1, and exhibits an open‐circuit voltage of −17.91 mV and output power of 38.1 nW at a temperature difference of 40 K. After being completely cut off, the hybrid thermoelectric hydrogel automatically recovers its electrical characteristics within a response time of 2.0 s, and the healed hydrogel remains more than 99% of its initial power output. Such stretchable and self‐healable hybrid hydrogel thermoelectric materials show promising potential for application in dynamic service conditions, such as wearable electronics.

Transport properties of few-layer NbSe2: From electronic structure to thermoelectric properties

4-layer NbSe2 is grown on SiO2 by molecular beam epitaxy. The in-situ X-ray photoelectron spectroscopy measurements suggest an Nb-rich stoichiometry (Nb1+xSe2) likely due to the intercalation of Nb atoms in between the NbSe2 layers. The metallic nature of the samples is confirmed using scanning tunneling microscopy and local density of state measurements as well as band structure calculations. This metallic nature is consistent with the small measured Seebeck coefficient and large electrical conductivity values. A change of sign in the Seebeck coefficient is observed in the bulk single crystal sample at 50 K, and in the polycrystalline few-layer sample at 120 K. Since the samples are metallic, this change of sign is the result of a change in the density of state slope at the Fermi level. The temperature dependence of the measured Seebeck coefficient matches with theoretical calculations for 4-layer NbSe2. The room temperature Seebeck coefficient is negative, but when oxidized, that of the few-layer sample changed to positive. The in-plane thermal conductivity of the few-layer samples is measured using the heat diffusion imaging method at low temperatures and is (32 ± 10) W/m∙K at 200 K.

DFT study of structural, mechanical, thermodynamic, electronic, and thermoelectric properties of new PdTiZ (Z = Ge and Pb) half Heusler compounds

AbstractA first principle investigation of structural, mechanical, thermodynamical, electronic, and thermoelectric properties of PdTiZ (Z = Ge and Pb) were carried out using the plane‐wave pseudopotential (PP‐PW) method. The exchange‐correlation between the electrons was considered with the generalized gradient approximation of Perdew‐Burke‐Ernzerhof (PBE‐GGA). The energy band structure of the sample materials shows that it is a semiconductor with indirect energy band gaps of 0.66 eV and 0.387 eV in PdTiGe and PdTiPb, respectively, with the density of states being mainly dominated by the p states of Z and d states of Ti atom in the vicinity of the Fermi energy level. The sample compounds were found to be mechanically and dynamically stable in their non‐magnetic cubic phase. PdTiGe was found to be harder and stiffer than PdTiPb. The thermodynamic study revealed that pressure has a negative effect on heat capacity, whereas Debye temperature increases with enhanced pressure in both the sample compounds. The thermoelectric properties of the sample compounds predicted that p‐type nature of the sample compounds possess better thermoelectric performance. The room temperature Seebeck coefficient (S) values were found to be 98.73 μV/K and 94.82 μV/K for PdTiGe and PdTiPb, respectively, whereas S values of 245.73 μV/K and 218.77 μV/K at 1200 K at n = 1021 cm−3. The lowest values of lattice thermal conductivity () of 2.28 W/m‐K and .98 W/m‐K were observed for PdTiGe and PdTiPb, respectively. The optimum dimensionless figure of merits of .66 (1200 K) and .64 (1000 K) were found for p‐type PdTiGe and PdTiPb, respectively, at optimum carrier concentration.

Two-dimensional quantum confinement effects on thermoelectric properties of MgO monolayers: A first principle study

In this paper, the thermoelectric properties of magnesium oxide in the bulk and monolayer (ML) phases in the two facets of (100) and (111) have been calculated and compared by using density functional theory (DFT) and Boltzmann theory. The electronic band structure calculations of bulk and monolayers of MgO indicate that the band gap for bulk and MgO(100) ML is direct, and indirect for MgO(111) ML Κ-to Γ-point. The estimated band gaps are in good agreement with other theoretical and experimental works. Due to the quantum confinement effects, two small peaks are observed in the n-doping region of the room temperature Seebeck coefficients of the monolayers which are not present in the bulk structure. In addition, we demonstrate that the room temperature figure of merit of MgO(100) ML has a remarkable peak at μ ​= ​2.71 ​eV with the value of about 1.5 which is attributed to its corresponding Seebeck coefficient peak. Beside, with increasing temperature, this peak shifts to the lower chemical potentials and reaches to 1.8 ​at ​T ​= ​800 ​K and μ ​= ​2.4 ​eV. Our findings show that a proper n-doping MgO(100) ML is a promising material for future thermoelectric applications at room and even high temperatures.

Band convergence and phonon engineering to optimize the thermoelectric performance of CaCd2Sb2

Alignment of valence bands has been demonstrated to be effective in promoting the thermoelectric performance of p-type AB2X2 zintl phases. In this work, the degeneracy of the valence bands is manipulated by alloying CaCd2Sb2 with CaMg2Sb2. It is found that the Γ(pxy) band and the Γ(pz) band were effectively converged in CaCd1.5Mg0.5Sb2. By further doping Ag at the Cd site, the carrier concentration can be maintained when the alloying concentration varies. The room-temperature Seebeck coefficient increased from ∼150 μV K−1 in CaCd2Sb2 to ∼190 μV K−1 in CaCd1.5Mg0.5Sb2 when the carrier concentration was maintained at ∼2.5 × 1019 cm−3. In addition, Cd/Mg substitutional point defects with substantial atomic mass difference induced significant phonon scattering; thus, a lattice thermal conductivity as low as ∼0.5 W m−1 K−1 was achieved at 750 K. Eventually, a peak zT value of ∼1.3 was realized in CaCd1.494Ag0.006Mg0.5Sb2.

The effects of alkaline-earth-metal-element doping on the thermoelectric properties of β-Zn4Sb3

The effects of alkaline-earth metal elements Ca, Sr, and Ba on the electronic structure and thermoelectric properties of β-Zn4Sb3 were investigated by performing self-consistent ab initio electronic structure calculations within density functional theory and solving the Boltzmann transport equations within the relaxation time approximation. The results demonstrate that these alkaline-earth metal elements with s orbitals could introduce giant sharp resonant peaks in the electronic density of states (DOS) near the host valence band maximum in energy. And these deliberately engineered DOS peaks result in a sharp increase of the room-temperature Seebeck coefficient of β-Zn4Sb3 by a factor of nearly 8/9/19, respectively. Additionally, with the simultaneous increase of conductivity and decline of carrier thermal conductivity upon Ca/Sr/Ba doping, potentially, at least, 10/4/2-fold increase in optimizing power factor, and 14/12/8-fold increase in thermoelectric figure of merit of β-Zn4Sb3 at room temperature are achieved. And their corresponding optimal Fermi levels are all located near the host valence band maximum.

Thermoelectric Characteristics of InAs Nanowire Networks Directly Grown on Flexible Plastic Substrates

III-V semiconductor nanowires have shown promise for thermoelectric applications, but their use in practical devices has conventionally been hindered by complex fabrication processes and device integration. Here, we characterize the thermoelectric properties of InAs nanowire networks directly grown on flexible polyimide plastic. The n-type nanowire networks achieve a high room-temperature Seebeck coefficient of −110.8 μV K–1 and electrical conductivity of 41 S cm–1, resulting in a thermoelectric power factor of 50.4 μW m–1 K–2. Moreover, the nanowire networks show remarkable mechanical flexibility with a relative change in resistance below 0.01 at bending radii below 5.2 mm. We further establish the thermoelectric performance of InAs nanowire networks on plastic using a facile proof-of-concept thermoelectric generator producing a maximum power of 0.44 nW at a temperature gradient of 5 K. The findings indicate that direct growth of III-V nanowire networks on plastic substrates shows promise for the development of flexible thermoelectrics applications.

Structure, electric and thermoelectric properties of binary ZnO-based ceramics doped with Fe and Co

We have studied the interconnection between structure (grain sizes, chemical and phase composition, porosity) and some electric properties (resistivity, Hall and Seebeck coefficients, as well as power factor, concentration and mobilities of carriers) in composite ceramics (ZnO)z[(TM)xOy]1-z (TM = Fe and Co – transition metals, 0 ≤ x ≤ 3; 1 ≤ y ≤ 4, 0.5 ≤ z ≤ 10 wt%), prepared by one-step and/or two-step annealing on air of powder mixtures of ZnO and TM oxides. The structure of ceramic samples was studied by X-ray diffraction (XRD), Mossbauer (MS) and Raman (RS) spectroscopies, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis and magnetometry. It was proved that phase composition of (ZnO)z[(TM)xOy]1-z ceramics depends on the type of doping agents. Addition of CoO to ZnO results in the formation of solid solutions with wurtzite structure after two-step annealing independently on Co concentration z ≤ 10 wt%. Addition of FexOy to ZnO results in the formation of the samples with three phase components after synthesis: submicron grains of wurtzute-like structure with large grains of ZnFe2O4 ferrite with spinel structure and residual oxides FexOy used as dopant in powder mixture. SEM measurements evidence that size of the wurtzite phase grains decreases from several tens of micrometers when using the one-step synthesis to a submicron level for the case of the two-step technology. Temperature dependences of electrical resistivity ρ(Т), as well as Hall and Seebeck coefficients in the undoped ZnO in th range of 6–500 K have shown a competition of the Mott and Shklovsky-Efros variable range hopping conductance (due to disordering), percolative one (due to formation of large-scaled potential relief) and a standard electron transport by Cband. It was found that Cband contribution to the carrier transport in ceramic samples (ZnO)z[(TM)xOy]1-z above 100 K was provided by both low and deep donor centers which have been formed in the wurtzite phase Zn1-δ(TM)δO. For example, in the TM doped samples we observed intrinsic shallow levels with ionization energies of about ΔE1 = (0.04–0.05) eV as well as extrinsic deep levels with ΔE2 = (0.24–0.37) eV. The iron doping of ZnO-based ceramic samples increased the room temperature Seebeck coefficient S(300 K) in average. In so doing, the S(300 K) dependence on electron concentration n of the studied samples (ZnO)z(FexOy)1-z approached maximal values (up to 1000 µV/K) at n = 1021 m−3. At the same time ZnO doping with Co resulted in more weak increase (up to 1.3–1.5 times) of S(300 K) values. Practically threefold growth of S(300 K) doe to Fe doping was attributed by us to the influence of particles of ferrite) formed in wurtzite matrix. The power factor P = (S2/ρ), estimated for the studied samples, evidenced that for both dopants it’s the highest values ( = 10−5 W/K·m) were approached in the (ZnO)z[(TM)xOy]1-z ceramics with the lowest resistivity values.

Origin of pseudo gap and thermoelectric signatures of semimetallic Ru2TaGa: Structural stability from phonon dynamics, mechanical, and thermodynamic predictions

We have studied the origin of the semimetallic pseudo gap and the role of site preference in the L21-type Heusler compound Ru2TaGa. A detailed account of the structural stability, phonon-dependent properties, electronic structure, and thermoelectric properties of the host compound is presented herein. Stability assessments have been made on the basis of phonon band structure, formation energy, mechanical criteria, and hull energy calculations. From the calculated density of states (DOS) and band structure, a semimetallic scenario is evident, with the Fermi level trapped in the pseudo gap. HSE calculations provide a decisive picture, with an indirect overlap between electron and hole pockets near the Fermi level of Ru2TaGa being responsible for the formation of a negative or pseudo gap. Comparison of the Ru eg and Ta t2g states reveals the role of d-d hybridization in pseudo gap formation in Ru2TaGa-like compounds. Additionally, we endeavor to discuss the transport coefficients of Ru2TaGa. The room temperature Seebeck coefficient calculated for Ru2TaGa is 66.42 μV/K, considerably larger than those of other semimetallic compounds of the same family. Considering the lattice thermal conductivity (κL = 2.5 W/mK) at 800 K, we obtain a significant figure of merit of ZT = 0.025 in Ru2TaGa. Although the absolute thermoelectric figure of merit (0.002) is relatively low in Ru2TaGa, it is still the highest among the non-doped full Heuslers of the same family hitherto reported.

High Room-Temperature Thermoelectric Performance of Honeycomb GaN Monolayer

Self-powered nanoscale devices that scavenge heat from the surrounding environment show great promise in applications as biosensors or environmental sensors. Recently, defect-free monolayer gallium nitride (GaN) with a honeycomb structure was realized experimentally. In this paper, based on first-principles calculations and Boltzmann transport theory, the thermoelectric properties of monolayer GaN are investigated. Its electronic structure characteristics approach the condition of Mahan–Sofo’s best thermoelectrics, which leads to outstanding room-temperature Seebeck coefficients, up to 310 μV·K−1 with a hole concentration of 5 × 1018cm−3. Combined with the intrinsic high electron mobility, it then boosts the power factor of the GaN monolayer system. Moreover, due to the strong in-plane polarization nature of Ga–N bonds, the in-plane lattice vibrations exhibit extremely large anharmonicity, resulting in low thermal conductivity (6.4 W·m−1·K−1 at 300K). These results immediately cause a room-temperature figure of merit ZT of 0.17, indicating the P-type monolayer GaN is a superior candidate for low-dimensional thermoelectrics.