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.