NaInX2 (X = S, Se) layered materials for energy harvesting applications: first-principles insights into optoelectronic and thermoelectric properties

Abstract

In recent times, layered chalcogenide semiconductors have attracted great interest in energy harvesting device applications. In the present study, the structural, electronic, optical and thermoelectric properties of two isostructural chalcogenide materials, NaInS 2 and NaInSe 2 with hexagonal symmetry (R-3m) have been studied using the first principles method. A very good agreement has been found between our results with the available experimental and theoretical ones. The studied materials are semiconducting in nature as confirmed from the electronic band structure and optical properties.The strong hybridizations among s orbitals of Na, In and Se atoms push the bottom of the conduction band downward resulting in a narrower band gap of NaInSe 2 compared to that of NaInS 2 compound. Different optical (dielectric function, photoconductivity, absorption coefficient, reflectivity, refractive index and loss function) and thermoelectric (Seebeck coefficient, electrical conductivity, power factor and thermal conductivity) properties of NaInX 2 (X = S, Se) have been studied in detail for the first time. It is found that all these properties are significantly anisotropic due to the strongly layered structure of NaInX 2 (X = S, Se). Strong optical absorption with sharp peaks is found in the far visible to mid ultraviolet (UV) regions while the reflectivity is low in the UV region for both the compounds. Such features indicate feasibility of applications in optoelectronic sector.The calculated thermoelectric power factors at 1000 K for NaInS 2 and NaInSe 2 along a-axis are found to be 151.5 W/cmK 2 and 154 W/cmK 2 , respectively and the corresponding ZT values are ~0.70. The obtained thermal conductivity along a-axis for both compounds is high (~22 W/mK).This suggests that the reduction of such high thermal conductivity is important to achieve higher ZT values of the NaInX 2 (X = S, Se) compounds.

Newly Synthesized Three-Dimensional Boron-Rich Chalcogenides B12X (X = S and Se): Theoretical Characterization of the Physical Properties for Optoelectronic and Mechanical Applications

“… 19 The choice of the pseudopotential is quite important in view of optimization of the crystal structure and its electronic structure, especially of the semiconductor materials. 6 , 20 , 21 The exchange–correlation potentials are evaluated by using the functional form of Perdew–Burke–Ernzerhof (PBE) type within the generalized gradient approximation (GGA) and also of Ceperly and Alder–Perdew and Zunger (CA-PZ) type within the local density approximation (LDA). 18 , 22 , 23 The optimizations for both chalcogenide crystal structures are done by the Broyden–Fletcher–Goldfarb–Shanno (BFGS) method 24 using the following optimization input parameters: a plane wave basis set kinetic energy cutoff of 550 eV, a Monkhorst–Pack k -point mesh size 25 of 6×6×3, an energy convergence threshold of 5 × 10 –6 eV/atom, a maximum force of 0.01 eV/Å, a maximum stress of 0.02 GPa, and a maximum atomic displacement of 5 × 10 –4 Å.…”

Origin of high hardness and optoelectronic and thermo-physical properties of boron-rich compounds B6X (X = S, Se): A comprehensive study via DFT approach

“…CASTEP code allows investigating the electronic properties using local and non-local exchange-correlations functionals. In most cases of semiconducting materials, the functionals of LDA-CAPZ and GGA-PBE underestimate the band gap [20,21]. It is reported that the Heyd-Scuseria-Ernzerhof hybrid functional (HSE06) is one of the approaches that is used to calculate a more accurate band gap of semiconducting materials [22][23][24][25].…”

“…EDD describes the variations in the electronic charge distribution owing to the formation of all the bonds within the crystal. We have studied the EDD and Mulliken atomic population (MAP) analysis between different atomic elements of these compounds, which are crucially important in order to understand charge transfer, bonding and its nature as well [26,27]. Fig.…”

“…Fig. 4: The (a) imaginary part, ε 2 (ω) and (b) real part, ε 1 (ω) of the dielectric functions for B 6 S and B 6 Se compounds as a function of photon energy.The photon energy dependent imaginary part of the dielectric function, ε 2 (ω) could be discussed based on the band structure and PDOS analysis[27]. The ε 2 (ω) usually describes the absorption phenomena of solids while the refractive index is indicated by the ε 1 (ω).…”

Physical properties of predicted MAX phase borides Hf2AB (A = Pb, Bi): A DFT insight

“…As this function signifies the energy loss of electrons during the propagation trough the materials, therefore, the zero value of L (ω) up to certain energy indicates no energy loss of electrons. The peak observed at certain energy depicts the character of plasma oscillation and defines the characteristic frequency that is known as the plasma frequency ω p of the material [97]. At ω p , the real part of the dielectric function, ε 1 (ω), becomes positive from below when the ε 2 (ω) < 1.…”