Novel thermoelectric performance of 2D 1T- Se₂Te and SeTe₂ with ultralow lattice thermal conductivity but high carrier mobility

Abstract

The design and search for efficient thermoelectric materials that can directly convert waste heat into electricity have been of great interest in recent years since they have practical applications in overcoming the challenges of global warming and the energy crisis. In this work, two new twodimensional 1T-phase group-VI binary compounds Se 2 Te and SeTe 2 with outstanding thermoelectric performances are predicted using first-principles calculations combined with Boltzmann transport theory. The dynamic stability is confirmed based on phonon dispersion. It is found that the spin-orbit coupling effect has a significant impact on the band structure of SeTe 2 , and induces a transformation from indirect to direct band gap. The electronic and phononic transport properties of the Se 2 Te and SeTe 2 monolayer are calculated and discussed. High carrier mobility (up to 3744.321 and 2295.413 cm 2 V −1 S −1 for electron and hole, respectively) is exhibited, suggesting great applications in nanoelectronic devices. Furthermore, the maximum thermoelectric figure of merit zT of SeTe 2 for n-type and p-type is 2.88, 1.99 and 5.94, 3.60 at 300 K and 600 K, respectively, which is larger than that of most reported 2D thermoelectric materials. The surprising thermoelectric properties arise from the ultralow lattice thermal conductivity k l (0.25 and 1.89 W m −1 K −1 for SeTe 2 and Se 2 Te at 300 K), and the origin of ultralow lattice thermal conductivity is revealed. The present results suggest that 1T-phase Se 2 Te and SeTe 2 monolayer are promising candidates for thermoelectric applications.

Biaxial Tensile Strain-Induced Enhancement of Thermoelectric Efficiency of α-Phase Se2Te and SeTe2 Monolayers

“…From Figure 5 , at given carrier concentration range, such as 10 19 to 10 20 cm −3 and 10 19 to 10 21 cm −3 for n- and p-type doping, respectively, all types of S approximately linear decreases with increasing carrier concentration, while σ increases with carrier concentration. This can also be found in many other 2D materials that S and σ have a different relationship to carrier concentration since they have an opposite dependency with the DOS near the Fermi surface [ 7 , 37 , 50 ]. Thus, we can obtain the optimized PF shown in Figure 6 by the relationship of , which is a vital parameter for the figure of merit and is discussed in the following.…”

“…For unstrained structure, the p-type doping ZT of Se 2 Te monolayers is superior to that of n-type doping, which is the opposite of that of SeTe 2 monolayers. The reason for this discrepancy is interpreted in detail in our previous work [ 7 ]. For strained structures, overall, the value of n-type and p-type ZT was visibly enhanced for both Se 2 Te and SeTe 2 monolayers compared to that of the unstrained structures.…”

“…Recent studies confirmed that the compounds composed of Te and Se have excellent thermoelectric and electronic transport properties [ 7 , 8 , 12 ]. In our previous work [ 7 ], we revealed that the 1T-phase Se 2 Te and SeTe 2 monolayers are promising medium-temperature thermoelectric materials; however, their room temperature conversion efficiency is inferior. Recently, numerous studies [ 13 , 14 , 15 , 16 ] proved that the tensile mechanic strain can induce the reduction of the lattice thermal conductivity and then enhancement of the thermoelectric performance of 2D materials.…”

“…In 2017, Zhu et al [ 4 ] and Chen et al [ 5 ] predicted and successfully synthesized the tellurene on highly oriented pyrolytic graphite (HOPG) substrates by using molecular beam epitaxy. Subsequently, a new two-dimensional (2D) materials family, the group-VI elemental 2D materials, has attracted significant attention due to its high carrier mobility, high photoconductivity, and thermoelectric responses [ 6 , 7 , 8 , 9 , 10 , 11 ]. Recent studies confirmed that the compounds composed of Te and Se have excellent thermoelectric and electronic transport properties [ 7 , 8 , 12 ].…”

“…Subsequently, a new two-dimensional (2D) materials family, the group-VI elemental 2D materials, has attracted significant attention due to its high carrier mobility, high photoconductivity, and thermoelectric responses [ 6 , 7 , 8 , 9 , 10 , 11 ]. Recent studies confirmed that the compounds composed of Te and Se have excellent thermoelectric and electronic transport properties [ 7 , 8 , 12 ]. In our previous work [ 7 ], we revealed that the 1T-phase Se 2 Te and SeTe 2 monolayers are promising medium-temperature thermoelectric materials; however, their room temperature conversion efficiency is inferior.…”