Insight into the physical characteristics of novel inorganic chalcogenides MAg3Se4 (M=V, Nb, Ta) with exceptional stability using WIEN2K for its applications in photovoltaics

Abstract

We develop environment friendly, renewable and effective energy sources to address the energy difficulties owing to the depletion of fossil fuels. So, inorganic chalcogenides are most intriguing compounds in the most advanced future solar cells for effective production of sustainable energy using solar radiations. This study represents the first theoretical exploration of MAg₃Se₄ (M = Nb, V and Ta). We describe their structural, magnetic, optical, mechanical and vibrational properties via Wien2k code for photovoltaic devices. GGA + U is utilized due to the fact that U is a suitable solution to incorporate on-site self-interactions of the electrons. The lattice constants $\left(\AA \right)$ are given as $a_o=5.9719$ for VAg₃Se₄, $a_o=6.0972$ for NbAg₃Se₄ and $a_o=6.1020$ for TaAg₃Se₄, respectively. These materials are semiconductors due to indirect electronic band gap of 0.92 eV (↑↓) in VAg₃Se₄, 1.75 eV (↑↓) in NbAg₃Se₄ and 2.15 eV (↑↓) in TaAg₃Se₄, respectively. Relatively, large cohesive energy (−3.96 eV/atom) ${\text{VAg}}_3{\text{Se}}_4$ is an indication of its structurally more stable. PDOS reveals Ag-4d and Se-4p orbitals are partaking in deep area of the valence band. Ta-d states are partaking in the conduction band beyond the Fermi level. Additionally, optical investigation reveals that these compounds barely reflect incident radiations as it strikes their surfaces. Mechanical properties demonstrate that examined chalcogenides display mechanical stability, ductile character and anisotropic behavior since its magnitude is not equal to 1. Phonons study indicates some imaginary frequency in NbAg₃Se₄ and TaAg₃Se₄ which may be caused by a specific direction of the cubic crystal structure, while no imaginary frequency is found for VAg₃Se₄. All these materials show thermodynamic stability because free energy graph enlarges to the negative energy range. Our results unveil that these chalcogenides can be beneficial for photovoltaics applications.