Tunable Electronic, Optical Properties, Charge, and Quantum Capacitance of <scp> MoSi ₂ N </scp> <i> _<i>x</i> </i> <scp> P ₄ </scp> _{− <i>x</i>} Monolayer for Device Application: A First‐Principles Study

ABSTRACT Janus 2D materials have many distinct properties because of lacking the mirror asymmetry. Electronic and optical properties, charge and quantum capacitance of MoSi 2 N x P 4− x monolayers are studied by density functional theory (DFT). MoSi 2 N 4 is an indirect semiconductor with bandgap of 1.84 eV, while MoSi 2 P 4 is a direct semiconductor. MoSi 2 N 2 P 2 is a Janus structure with N‐face versus P‐face, and exhibits half‐metallic character. Dirac cone is observed for MoSi 2 NPPN, which originates from Mo‐d, N‐p, and P‐p states. Built‐in electric field appears in Janus systems, and MoSi 2 NPNN has an internal electric field of 0.14 eV/Å. All systems have larger absorption for visible light, especially for MoSi 2 PNNN with 22.55%. The systems with more P atoms have better electrical conductivity, and MoSi 2 P 4 has the best electrical conductivity. MoSi 2 NNPP, MoSi 2 NPPN, MoSi 2 PNNN and MoSi 2 NPNP are anode materials, while other systems are favorable for cathode materials in aqueous system.