Structural, electronic, piezoelectric, and optical properties of Janus MoSi2Z3X (Z/X = N, P, As) monolayers

Janus structural engineering of two‐dimensional (2D) materials has emerged as a pivotal strategy for modulating their physicochemical properties. In this work, we designed new Janus MoSi₂Z₃X (Z/X = N, P, As) monolayers and systematically investigated their structural, electronic, carrier mobility, piezoelectric, and optical properties by first‐principles calculations. The results demonstrate that MoSi₂P₃N, MoSi₂P₃As, and MoSi₂As₃P monolayers exhibit robust dynamical, thermodynamic, and mechanical stability. The band structure reveals that MoSi₂P₃N (MoSi₂P₃As) is an indirect bandgap semiconductor with its valence band maximum (VBM) at the K (Γ) point and conduction band minimum (CBM) at the M (K) point, whereas MoSi₂As₃P is a direct bandgap semiconductor with both VBM and CBM located at the K point. Besides, biaxial strain engineering enables the phase transition from semiconductor-to-metal accompanied with an indirect‐to-direct bandgap transition in MoSi₂P₃N and a direct‐to-indirect transition in MoSi₂As₃P. Furthermore, these monolayers demonstrate anisotropic and high carrier mobility, especially the hole mobility of MoSi₂P₃N approaching 10³ cm² V⁻¹ s⁻¹. Specially, MoSi₂P₃N, MoSi₂P₃As, and MoSi₂As₃P monolayers exhibit excellent piezoelectric performance, especially, the piezoelectric strain coefficients d₁₁ and d₃₁ of MoSi₂P₃N are 6.61 and 0.12 pm/V, respectively. Furthermore, they display high optical absorption across both visible and ultraviolet spectral regions. These findings highlight the potential applications of Janus MoSi₂Z₃X monolayers in piezoelectric and photoelectric devices.