Sodium-based di-chalcogenide: a promising material for tandem solar cells

Compounds based on chalcogen elements are widely studied currently due to their many interesting applications for electronic devices. The sodium-based dichalcogenide (NaNbS₂) is a fascinating material with storage and conversion energy applications. In this paper, we conduct a first-principles investigation of the structural and thermodynamic stability and electronic properties of this material. We analyze a total of four structures to find the ground state using a fourth-order Birch-Murnaghan equation of state: the α and η related to the A-phase and the ζ ₁ and ζ ₂ related to the B-phase. We carefully address the exchange-correlation effects using the semi- local GGA-PBEsol targeted for solids. To analyze the electronic structure with higher accuracy, we implement the quasi-particle G o W o approximation. Our results for the fourth-order Birch-Murnaghan equation show that the most thermodynamically stable phase at zero temperature is α. To provide experimentalists insights about the possible routes to grow these materials, we calculated the convex hull of the α-model and ζ ₁-model, finding that both are energetically stable. Finally, the calculated band gap with quasiparticle corrections for the α-model is 1.03 eV, which suggests possible applications of this material as a bottom cell in modern solar cells.