Ultraviolet active novel chalcogenides AScSe2 (A= K, Cs): The structural, optoelectronic, mechanical, vibrational, and thermodynamical properties for energy harvesting applications

Abstract

It is essential nowadays to investigate some unique and appropriate materials for optoelectronic applications. We deliberate here for the first time, the structural, optoelectronic, mechanical, vibrational, and thermodynamical properties of hexagonal structured selenium-based ternary chalcogenides AScSe2 (A = K, Cs) by using Perdew-Burke-Ernzerhof Generalized-Gradient-Approximation (PBE-GGA). The lattice angles for these materials are found as α = β = 90° and γ = 120°. KScSe2 is optimized with lattice parameters a = b = 4.3 (Å), c = 7.81 (Å) whereas, CsScSe2 is relaxed at a = b = 4.43 (Å) and c = 8.51 (Å). The hybrid Heyd-Scuseria-Ernzerhof (HSE06) functional overestimates the lattice parameters to the extent that for KScSe2 these are found as a = b = 4.92 (Å), c = 7.10 (Å) and for CsScSe2 a = b = 5.15 (Å), c = 7.09 (Å). The energy band gap confirms the semiconducting nature of these materials. Born's criteria endorses the mechanical stability of these materials. Moreover, the temperature dependence of thermodynamic potentials and specific heat at constant volume is also determined using the harmonic approximation. The negative value of free energy ensures their thermodynamical stability. The vibrational modes are calculated by plotting the phonon dispersion and the vibrational density of states (VDOS) where infrared (IR) and Raman spectroscopy are used to characterize the vibrational modes. The optical parameters are examined at a smearing value of 0.5 eV that portray good absorptivity of the incident light from the Ultraviolet (UV) region. Thus, these materials may be potential ones to be utilized for energy harvesting applications via photovoltaic.