First-principles calculations of electronic, optical and thermoelectric properties of the Ge2SeS/GeSe van der Waals heterostructure

In this research, we systematically investigate the electronic structure, optical and thermoelectric properties of the Ge₂SeS/GeSe van der Waals (vdW) heterostructure in comparison to the Ge₂SeS and GeSe monolayers by using density functional theory (DFT) implemented in Quantum ESPRESSO. We have constructed two configurations of the Ge₂SeS/GeSe heterostructure by stacking the Ge₂SeS monolayer on top of the GeSe monolayer (Stacking A₁ and A₂). According to our calculations, the calculated indirect electronic band gaps of both Stacking A₁ and Stacking A₂ are E_g = 0.80 eV and 0.88 eV, respectively. The transfer of charges from the Ge₂SeS to the GeSe monolayer for both configurations has been predicted. By Bader charge analysis, the charge transfers for Stacking A₁ and A₂ are approximately 0.013 e and 0.020 e, respectively. The coefficient of absorption for the Ge₂SeS/GeSe heterostructure is higher than that for Ge₂SeS and GeSe monolayers in both regions of the spectrum (visible, and UV). Moreover, the Ge₂SeS/GeSe heterostructure has a very good absorbing capability of light in the visible region up to 85 × 10⁴ cm⁻¹. Our calculations yielded a high thermoelectrical electronic figure of merit (ZT_e) of 12.64 and 2.27 for Stacking A₁ and A₂, respectively. As a result, our findings show that the Ge₂SeS/GeSe heterostructure is a promising material for thermoelectric and optoelectronic applications.