Ultrahigh Power Factor and Ultralow Thermal Conductivity at Room Temperature in PbSe/SnSe Superlattice: Role of Quantum‐Well Effect

Abstract

As experimentally shown by Hicks and Dresselhaus [16] the value of S is about 2.5 times than that of the bulk through quantum confinement effects by using QW structures. In 2007, Ohta et al. [17] observed a large Seebeck coefficient S = 850 µV K −1 in SrTiO 3 (barrier)/ SrTi 0.8 Nb 0.2 O 3 (well)/SrTiO 3 (barrier) multiple QW (MQW). By analyzing the optical spectra, Choi et al. found that the polaron plays an important role in determining the electronic structure in this MQW. [18] Through orbital reconstruction, recently Geisler et al. [19] also obtained large positive S (≈135 µV K −1 ) in LaNiO 3 /SrTiO 3 MQW at room temperature. As a matter of fact, for oxide or semiconductor MQW structure, the carrier electrons should be confined inside of a thin conducting layer. [16,17] There is valid argument for the attention that this will modified the electronic structure near Fermi level through polaron dimensional effect or quantum confinement effect. [18,20] In addition to high S, another strongly desired characteristic for TE materials is electrical and thermal conductivity, which will allow us to explore the high figures of merit. Venkatasubramanian et al. [21] reported that figure of merit can be further increased by controlling the transport of electrons in Bi 2 Te 3 / Sb 2 Te 3 superlattices. In addition, recently theoretical analyses for WS 2 /WSe 2 suplattices suggest that the ZT values can be enhanced by optimal the thermal conductivity. [22,23] However, for the earlier work of the semiconductor QW structure, the band offset is small and which most likely minimal the anisotropy between in-plane and out-of-plane electrical conductivities. [21,[24][25][26] Under this circumstance, due to the electron tunneling and thermal currents between the layers with these infinite potential barriers heights, the enhancement of the ZT values are rather moderate. On the other hand, for the oxide QW, although the tunneling effect are disappeared, but the thermal conductivity are 1-2 orders of magnitude higher than the semiconductor, [27,28] which limits their application in thermoelectric device.In this paper, we select the PbSe and SnSe as the constituent materials for the MQW structure to enhance Seebeck coefficient and optimal thermoelectric properties. PbSe has excellent thermoelectric properties in the mid-temperature region, along with low lattice thermal conductivity and small forbidden band width (≈0.28 eV). In this heterojunction system, SnSe was chosen as the potential barrier layer because on the one Reduced dimension is one of the effective strategies to modulate thermoelectric properties. In this work, n-type PbSe/SnSe superlattices with quantum-well (QW) structure are fabricated by pulsed laser deposition. Here, it is demonstrated that the PbSe/SnSe multiple QW (MQW) shows a high power factor of ≈25.7 µW cm −1 K −2 at 300 K, four times larger than that of PbSe single layers. In addition, thermal conductivity falls below 0.32 ± 0.06 W m −1 K −1 due to the phonon scattering at interface when the PbSe well thickness...

Tailoring Interfacial Charge Transfer for Optimizing Thermoelectric Performances of MnTe‐Sb2Te3 Superlattice‐Like Films

“…Moreover, for the (MnTe) x (Sb 2 Te 3 ) y SLs with x = 1 and 3, satellite peaks (labeled as 1th and 2th peaks) relevant to periodically modulated SL structure are discovered near the main peak (the 0th peak), as shown in Figure 1d. The thickness of SL modulation period Λ (i.e., the thickness of a single SL period) of (MnTe) x (Sb 2 Te 3 ) y SLs could be calculated by the following equation: [ 30,35 ] $$\[ \begin{array}{*{20}{c}}{\frac{{2\left( {\sin {\theta _n} - \sin {\theta _{{\rm{SL}},0}}} \right)}}{\lambda } = \frac{n}{\Lambda }}\end{array} \]$$where λ is the wavelength of X‐ray (λ Cu‐K α = 0.15405 nm), and θ n and θ SL,0 are the angular position of n th satellite peak and the main peak, respectively. According to Figure 2d and Equation (1), the Λ calculated from XRD patterns are 3.42, 6.16, 9.75, and 12.36 nm for SLs of (MnTe) 1 (Sb 2 Te 3 ) 3 , (MnTe) 1 (Sb 2 Te 3 ) 6 , (MnTe) 1 (Sb 2 Te 3 ) 9 and (MnTe) 1 (Sb 2 Te 3 ) 12 , respectively.…”

“…Moreover, for the (MnTe) x (Sb 2 Te 3 ) y SLs with x = 1 and 3, satellite peaks (labeled as 1th and 2th peaks) relevant to periodically modulated SL structure are discovered near the main peak (the 0th peak), as shown in Figure 1d. The thickness of SL modulation period Λ (i.e., the thickness of a single SL period) of (MnTe) x (Sb 2 Te 3 ) y SLs could be calculated by the following equation: [30,35] n n θ θ λ ( )…”

Toward Ultrahigh Thermoelectric Performance of Cu2SnS3‐Based Materials by Analog Alloying

“…Among them, the 𝜅 e (in Figure S8b, Supporting Information) is calculated via Wiedemann-Franz law 𝜅 e = LT/𝜌, where L is the Lorenz number (in Figure S8c, Supporting Information) obtained from S according to the single parabolic band (SPB) model. [10,46] [10,46]Calculated by the relation of 𝜅 L = 𝜅 total -𝜅 e , the temperature-dependent 𝜅 L is displayed in Figure 5b. The 𝜅 L of all the samples decreases with increasing temperature, approximately following the relationship of T −1 , which implies the reduction mainly sources from the U-process phonon-phonon scattering.…”

Modulated Fermi Level and Relaxed Lattice Strain Leading to Enhanced Thermoelectric Properties in AgSbSe2

“…Accordingly, a good thermoelectric material should simultaneously have a large Seebeck coefficient S, a high electrical conductivity σ, and a low thermal conductivity κ. 12 However, it is difficult to improve the thermoelectric performance by adjusting these parameters independently, and the reason lies in the strong coupling among these parameters. 13 At present, for materials with a good electrical transport performance, one usually tends to improve its thermoelectric properties by reducing the thermal conductivity through introducing point defect scattering, 14−16 grain boundary scattering, and dislocation stress scattering, among others; 17−21 in contrast, for materials with extrinsically low thermal conductivity, one always tries to optimize the overall thermoelectric properties via improving its electrical conductivity by doping, 22,23 energy band engineering, and interface engineering, among others.…”

“…In order to overcome the growing energy crisis and environment pollution nowadays, it is of great significance to develop sustainable and environmentally friendly energy sources. , Thermoelectric technique has attracted extensive attention because it can realize the direct and reversible conversion of heat and electricity. − Generally, the quality of a thermoelectric material is assessed by its figure of merit ZT defined as ZT = S 2 σ T /κ, where σ is the electrical conductivity, S is the Seebeck coefficient, κ is the thermal conductivity consisting of lattice thermal conductivity κ lat and electronic thermal conductivity κ e , − and T is the absolute temperature, individually. Accordingly, a good thermoelectric material should simultaneously have a large Seebeck coefficient S , a high electrical conductivity σ, and a low thermal conductivity κ . However, it is difficult to improve the thermoelectric performance by adjusting these parameters independently, and the reason lies in the strong coupling among these parameters .…”