Novel Two dimensional MA₂N₄ (M=transition metal, A=Si, Ge) Materials for Renewable Energy Applications

In the present work, based on first-principles calculations we explored members of the recently proposed new two-dimensional MA₂Z₄ (M=Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W; A= Si, Ge) family and classified them for different applications. Furthermore, electronic structure accurate hybrid HSE functionals and detailed descriptor property calculation of these compounds scrutinize the best possible compounds. Among these materials, MoGe₂N₄ and HfSi₂N₄ exhibit a reasonably high optical absorption coefficient and optical transition strength from the valence band to conduction band confirm its suitability for solar harvesting applications. However, the two-dimensional nature of both MoGe₂N₄ and HfSi₂N₄ reveal strong excitonic effects, as confirmed by GW+BSE calculations. Thickness-dependent spectroscopic limited maximum efficiency of MoGe₂N₄ turns out to be around 15.40 %, thus proposing the possibility to be a potential candidate for photovoltaic application. On the other hand, a suitable band edge position with respect to CO₂ reduction potential and effective CO₂ activation on HfSi₂N₄ recommend it for photocatalytic CO₂ reduction. Interestingly, NbSi₂N₄ exclusively exhibits a recently proposed bipolar magnetic character and enables its active use for spin transport-based applications.