To assess the feasibility of the organic–inorganic perovskite iodides ABI3 (A = CH3NH3, NH2CHNH2; B = Sn, Pb; X = I) for thermoelectric applications, we estimated their figures of merit (ZTs) as well as that of Bi2Te3, which is optimized for temperatures around 300 K, as a function of chemical potential on the basis of density functional theory calculations. Our analysis employed the tetragonal structures (P4mm) of (CH3NH3)PbI3 and (CH3NH3)SnI3, the trigonal (P3m1) structure of (NH2CHNH2)PbI3, and the orthorhombic (Amm2) structure of (NH2CHNH2)SnI3 to examine their thermoelectric properties around room temperature. Our work reveals that the ZTs of electron-doped ABI3 perovskites can be as large as that of hole-doped Bi2Te3 whereas those of hole-doped ABI3 are rather smaller so that, in thermoelectric performance, electron-doped perovskites ABI3 can be as good as hole-doped Bi2Te3.

Organic–inorganic hybrid perovskites ABI3 (A = CH3NH3, NH2CHNH2; B = Sn, Pb) as potential thermoelectric materials: a density functional evaluation

We have investigated the valley degeneracy of $\mathrm{Mo}{\mathrm{S}}_{2}$ multilayers and its effect on thermoelectric power factors. By modulating the layer thickness and external electric field strength, the hole valleys in the highest energy valence band at $\mathrm{\ensuremath{\Gamma}}$ and $K$ points and the electron valleys in the lowest energy conduction band at $K$ and ${\mathrm{\ensuremath{\Sigma}}}_{min}$ points are shifted differently. The hole valley degeneracy is observed in $\mathrm{Mo}{\mathrm{S}}_{2}$ monolayer, while that of electron valley is in $\mathrm{Mo}{\mathrm{S}}_{2}$ bilayer and monolayer under the external electric field. By tuning the valley degeneracy, the Seebeck coefficient and electrical conductivity can be separately controlled, and the maximum power factor can be obtained in $n$-type ($p$-type) $\mathrm{Mo}{\mathrm{S}}_{2}$ monolayer with (without) the external electric field. We suggest that the transition metal dichalcogenides are good examples to investigate the role of valley degeneracy in the thermoelectric and optical properties with the control of interlayer interaction and external electric field strength.

Control of valley degeneracy in Mo S 2 by layer thickness and electric field and its effect on thermoelectric properties

Two-dimensional transition metal dichalcogenides show great potential as promising thermoelectric materials due to their lower dimensionality, the unique density of states and quantum confinement of carriers. Here the effects of mechanical strain on the thermoelectric performances of monolayer WS2 have been investigated using density functional theory associated with semiclassical Boltzmann transport theory. The variation of the Seebeck coefficient and band gap with applied strain has followed the same type of trend. For n-type material the relaxation time scaled power factor (S2σ/τ) increases by the application of compressive strain whereas for p-type material it increases with the application of tensile strain due to valley degeneracy. A 77% increase in the power factor has been observed for the n-type material by the application of uniaxial compressive strain. A decrease in lattice thermal conductivity with the increase in temperature causes an almost 40% increase in ZT product under applied uniaxial compressive strain. From the study, it is observed that uniaxial compressive strain is more effective among all types of strain to enhance the thermoelectric performance of monolayer WS2. Such strain induced enhancement of thermoelectric properties in monolayer WS2 could open a new window for the fabrication of high-quality thermoelectric devices.

/pdf/strain-induced-valley-degeneracy-a-route-to-the-enhancement-56io3frjkl.pdf

Strain induced valley degeneracy: a route to the enhancement of thermoelectric properties of monolayer WS2

Investigations of electronic and thermoelectric properties of half-Heusler alloys XMgN (X = Li, Na, K) by first-principles calculations

The electronic, transport, optical, thermoelectric, and thermodynamic properties of the two-dimensional (2D) stable monolayer of boron arsenide (BAs) sheets have been investigated using state-of-art theoretical calculations. The energetic, dynamic, thermal, and mechanical stability of the BAs sheet have also been studied to unravel the feasibility of experimental realization of this material. Interestingly, the band gap of this semiconducting sheet changes from direct into indirect band gap material by the application of biaxial strain of 10% and it becomes metallic at 14% of biaxial strain. Furthermore, positive phonon vibrational modes have been observed for all applied biaxial strains, which ensure the stability of the sheet under strain. The semiconducting property is preserved when cutting 2D sheet into one-dimensional nanoribbons, and the band gap is size dependent. In addition, the calculated optical properties exhibit strong anisotropy. BAs nanomaterial has strong adsorption in the UV-visible region. The calculated Seebeck coefficient and power factor values show that BAs sheet is an ideal candidate for thermal management and thermoelectric applications. Finally, the thermodynamic properties have been calculated on the basis of the phonon frequencies. These rich properties of BAs nanosheets endow the system with promising applications in nanoelectronics and photovoltaics.

Exploring Multifunctional Applications of Hexagonal Boron Arsenide Sheet: A DFT Study

The layered semiconductors Bi2O2Q (Q = S, Se) consists of Bi2O2 layers sandwiched by Q square nets. On the basis of density functional theory calculations, we examined the thermoelectric properties of Bi2O2S, Bi2O2Se as well as hypothetical structure of Bi2O2(S0.5Se0.5) consisting of mixed chalcogen nets. The thermoelectric power factor of Bi2O2S0.5Se0.5 is much greater than those of Bi2O2S and Bi2O2Se, suggesting that introducing mixed chalcogen net in Bi2O2Q is a possible way of enhancing the thermoelectric property of Bi2O2Q.

Enhancing the Thermoelectric Properties of Layered Bi 2 O 2 Q (Q = S, Se): the Effect of Mixed Chalcogen Net

Density functional theory investigation of the electronic structure and thermoelectric properties of layered MoS2, MoSe2 and their mixed-layer compound

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Enhancing the Thermoelectric Properties of Layered Bi 2 O 2 Q (Q = S, Se): the Effect of Mixed Chalcogen Net

Density functional theory investigation of the electronic structure and thermoelectric properties of layered MoS2, MoSe2 and their mixed-layer compound