Unveiling Na2Fe2S2O oxychalcogenide: a high-performance thermoelectric and optoelectronic material for sustainable energy conversion

Abstract

Commercial use of thermoelectric devices is constrained due to the low efficiency of thermoelectric materials over a mid-to-high temperature range (∼650–923 K). There is a need for efficient materials, which show superior performance to overcome the energy crisis. In the present study, a theoretical approach (FP-LAPW) was employed to investigate the structural configuration, magnetic behavior, effective charge, bond order, electron charge density, and electronic, optical and thermoelectric properties of a newly synthesized layered Na₂Fe₂S₂O oxychalcogenide. The structural analysis showed that the Fe–O bonds played a significant role in the stability of the studied compound. Electronic properties revealed that Na₂Fe₂S₂O showed antiferromagnetic (AFM) Mott-insulating behavior. The computed energy band gap of Na₂Fe₂S₂O was 0.44 eV. The significant refractive index (n(ω)) values of 2.65 in the ab-plane and 2.75 along the c-axis at 2.65 eV (in the visible range) highlighted the strong potential of Na₂Fe₂S₂O for optoelectronic applications. The low reflectivity (20–23%) in the visible spectrum makes Na₂Fe₂S₂O well-suited for solar panels. The computed ZT value of Na₂Fe₂S₂O at 900 K was 1.09 and had the highest value of η_max of ∼11.75%, which suggested that this material could be used as a promising candidate for thermoelectric generators over mid-to-high temperatures.