Composition‐Dependent Absorption of Radiation in Semiconducting MSi2Z4 Monolayers

The recent synthesis of monolayer MoSi2N4, along with theoretical predictions encompassing the entire family of its chemical analogs, has opened up a new array of low‐dimensional materials for a diverse range of optoelectronics and photovoltaics applications. In this first‐principles many‐body study, the quasiparticle electronic structure of the material class MSi2Z4 (M = Mo, W, and Z = N, P, As, Sb) is analyzed. All monolayers display a direct bandgap at the K point, with the exception of MoSi2N4. In the tungsten‐based compounds, the fundamental gap can be adjusted by composition over a significantly broader energy range compared to their Mo‐based counterparts. Additionally, upon increasing atomic weight of the Z, both bandgap and exciton‐binding energies decrease. A noteworthy feature is the absence of a lateral valley near the conduction band minimum, indicating potential higher photoluminescence efficiencies compared to conventional transition‐metal dichalcogenide monolayers. The optical spectra of the considered materials are characterized by tightly bound excitons, leading to an absorption onset in the visible range (for N‐based) and in the infrared region (for all the others). This diversity offers promising opportunities to incorporate these materials and their heterostructures into functional optoelectronic devices such as tandem solar cells.