Theoretical Investigation of Metal-Shrouded Tl₂O Monolayers: Pudding-Mold-Type Band Structure and Thermoelectric Performance

Abstract

Inspired by the recent prediction of high carrier mobility and moderate energy gap in the metal-shrouded 2D semiconductor Tl2O [Ma, Y.; et al. J. Am. Chem. Soc. 2017, 139, 11694–11697], we present a theoretical analysis of thermoelectric properties for monolayer Tl2O by semiclassical Boltzmann transport theory. The “pudding-mold-type” valence band structure brings about a high p-type power factor (PF). A low lattice thermal conductivity (k l ) 2.4 W m–1 K–1 for T = 300 K is obtained because of the coupling among optical and acoustic vibration modes and the strong phonon scatterings. Upon combination of the superior PF with the low k l , high figure of merit (ZT) values 3.35 (n-type) and 4.20 (p-type) are achieved for T = 900 K, exceeding those of usual transition metal dichalcogenides monolayers and being comparable with that of the recently fabricated Bi2O2Se monolayer. These results reveal the potential applications of metal-shrouded monolayer Tl2O as a 2D high-performance thermoelectric material.

Monolayer Ag2S: Ultralow Lattice Thermal Conductivity and Excellent Thermoelectric Performance

“…Indeed, a band edge with flat and dispersive portions often results in an efficient thermoelectric material. 25 For example, high S 2 σ has been reported for monolayer Pd 2 Se 3 , 26 monolayer Tl 2 O, 18 Na x CoO 2 , 27 Fe 2 YZ Heusler compounds, 28 and BaPdS 2 . 29 Figure 3 shows the in-plane electron transport coefficients for electron and hole concentrations from 10 10 to 10 14 cm −2 at different temperatures.…”

“…Indeed, a band edge with flat and dispersive portions often results in an efficient thermoelectric material . For example, high S 2 σ has been reported for monolayer Pd 2 Se 3 , monolayer Tl 2 O, Na x CoO 2 , Fe 2 YZ Heusler compounds, and BaPdS 2 …”

“…The thermoelectric behavior of metal-shrouded monolayer Tl 2 O has been explored by first-principles calculations, , finding low κ l = 0.8(0.65) W m –1 K –1 along the x ( y )-direction at 300 K. At optimal hole doping and 300 K, therefore, high ZT of almost 2 can be achieved. Very recently, the first semiconducting nonmetal-shrouded monolayer material, monolayer Ag 2 S, has been predicted to have an indirect band gap of 2.84 eV (Heyd–Scuseria–Ernzerhof functional) .…”

Excellent Room-Temperature Thermoelectricity of 2D GeP3: Mexican-Hat-Shaped Band Dispersion and Ultralow Lattice Thermal Conductivity

“…The κ e is conducted by the Wiedemann-Franz law κ e = LσT, here, L = 2.44 × 10 −8 WΩK −2 represents the Lorentz number [26]. The carrier relaxation time τ is estimated by the deformation potential theory, which has been extensively applied for 2D systems [6,27,28]. The calculated electron (hole) relaxation time at room temperature is 1.9 (6.2) × 10 −13 s, which is close to the results obtained by Zeng et al [29].…”

Rashba Effect and Raman Spectra of Tl$_2$O/PtS$_2$ Heterostructure

“…Monolayer Tl 2 O is a recently proposed 2D metal-oxide semiconductor with cleavage energy comparable to well-known TMDCs. 28 Several theoretical studies highlighted its potential in catalysis, 29 valleytronics, 30 and especially in thermoelectrics 31,32 due to the ultralow lattice thermal conductivity. 33 Bulk Tl 2 O crystallizes in the 1T-phase with its cousin polytype also existing in 2H-phase albeit higher in energy 34 thus favoring the synthesis of the former due to energetic reasons.…”