High Thermoelectric Performance of Al₂X₂Se₂ (X = Cl, Br, I) Monolayers with Strong Anisotropy in Lattice Thermal Conductivity

Abstract

Recently, a class of thermoelectric (TE) materials with a FeOCl-type layered structure have been reported, such as GaOI, InOI, and TaCX (X = Cl, Br, I). These reports simulated further research on screening excellent TE monolayers with FeOCl-type structures. In this work, we carry out a comprehensive study on exploring the thermoelectric properties of Al2X2Se2 (X = Cl, Br, I) monolayers. The heat transport properties of the three monolayers are calculated and compared. Specifically, the thermal conductivities of 7.94 (16.98) W m–1 K–1 and 5.01 (16.15) W m–1 K–1 for the Al2Cl2Se2 and Al2Br2Se2 monolayers in the x direction (y direction) are obtained, respectively, which are more than that (0.29 (0.70) W m–1 K–1) for the Al2I2Se2 monolayer. The significant difference in the lattice thermal conductivity κl of Al2X2Se2 monolayers is attributed to their different phonon anharmonicity. It is also noted that strong anisotropy exists in the κl between the x and y directions. Additionally, the electronic transport parameters (the Seebeck coefficient and electrical conductivity) are figured out. Thus, the optimal ZT values of Al2X2Se2 monolayers from 200 to 700 K are obtained. It is found that the highest ZT value of the Al2I2Se2 monolayer (3.24) in the x direction is almost two times as higher as that (1.78) in the y direction at 700 K. The maximum ZT values of the Al2Cl2Se2 (0.59) and Al2Br2Se2 (0.95) monolayers in the y direction are higher than those of the Al2Cl2Se2 (0.34) and Al2Br2Se2 (0.77) monolayers in the x direction at 700 K, respectively, which are smaller than that of the Al2I2Se2 monolayer along with whether the x-axis (3.37) or the y-axis (1.75). This work reveals that the three monolayers exhibit anisotropies in the κl and ZT. The Al2I2Se2 monolayer has better TE performance than the Al2Cl2Se2 and Al2Br2Se2 monolayers.

Anisotropic Optical, Mechanical, and Thermoelectric Properties of Two-Dimensional Fullerene Networks

“…Based on the deformation potential theory, the electron relaxation time τ is calculated as listed in Table . The maximum relaxation time is caused by holes in the x direction, which is on the same order of magnitude with recently reported thermoelectric materials, such as X 2 Y 2 Z 2 type monolayers (100–160 fs). − Moreover, the behavior of the Seebeck coefficient indicates the possibility of fabricating low temperature thermoelectric devices with α-C 60 -2D as shown in Figure g. Note that Figure h reveals a strong Seebeck coefficient at middle–low temperature.…”

Strong anisotropy of Sc2X2Se2 (X = Cl, Br, I) monolayers contributes to high thermoelectric performance

“…Notably, the κ l of Sc 2 X 2 Se 2 exhibits obvious anisotropy, and the value along the x direction is noteworthily low. In fact, similar anisotropy of κ l has also been observed in other FeOCl-type monolayers 20,22,35 (as listed in Table 2). In addition, Sc 2 I 2 Se 2 has a lower κ l value than Sc 2 Cl 2 Se 2 and Sc 2 Br 2 Se 2 along both the x - and y -axes.…”

“…Similar to other FeOCl-type monolayers with an A 2 B 2 X 2 structure, 20–23 the Sc 2 X 2 Se 2 (X = Cl, Br, I) monolayers exhibit a 2D orthorhombic phase with a Pmmn (No. 59) space group.…”

NaBeAs and NaBeSb: Novel Ternary Pnictides with Enhanced Thermoelectric Performance

“…The max-ZT values in the z -direction are primarily due to the very low lattice thermal conductivity and maximum PF. They can compete with the recently discovered novel thermoelectric materials T-Au 6 S 2 (3.79 at 700 K) and Al 2 I 2 Se 2 (3.37 at 700 K) . Furthermore, our calculated ZT is fairly similar to that of industry-standard thermoelectric compounds, such as SnSe (2.6 at 923 K), Bi 2 O 2 Se (5.9 at 800 K), and PbTe (2.44 at 700 K), respectively.…”

“…80 and Al 2 I 2 Se 2 (3.37 at 700 K). 81 Furthermore, our calculated ZT is fairly similar to that of industry-standard thermoelectric compounds, such as SnSe (2.6 at 923 K), 31 Bi 2 O 2 Se (5.9 at 800 K), 82 and PbTe (2.44 at 700 K), 83 respectively. More interestingly, the max-ZT in n-type NaBeSb occurs at a doping concentration of 1.73 × 10 19 (2.03 × 10 19 ) cm −3 at 300(600) K, which indicates that it is easier to obtain excellent thermoelectric properties in the z-axis direction by modulating the electron doping.…”