Novel Two-Dimensional MA₂N₄ Materials for Photovoltaic and Spintronic Applications

We have systematically investigated a family of newly proposed two-dimensional MA₂N₄ materials (M = Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W; A = Si, Ge) using first-principles calculation. We categorize the potential of these materials into three different applications based on accurate simulation of band gap (using Hybrid HSE06 functional) and the associated descriptors. Three candidate materials (MoGe₂N₄, HfSi₂N₄, and NbSi₂N₄) turn out to be extremely promising for three different applications. MoGe₂N₄ and HfSi₂N₄ monolayers show strong optical absorption in the visible range, including high transition probability from the valence to conduction band. The GW+BSE calculations confirm a strong excitonic effect in both the systems. With a band gap of 1.42 eV, multilayer MoGe₂N₄ shows reasonably large simulated efficiency (∼15.40%) and hence can be explored for possible photovoltaic applications. High optical absorption, suitable band gap/edge positions, and the CO₂ activation make HfSi₂N₄ monolayer a promising candidate for photocatalytic CO₂ reduction. NbSi₂N₄, on the other hand, belongs to a new class of spintronic material called a bipolar magnetic semiconductor, recommended for spin-transport-based applications.