High hole mobilities in two dimensional monolayer MSi2Z4 (M = Mo/W; Z = P, As, Sb) for solar cells

Abstract

Recently, centimeter-scale monolayer MoSi₂N₄ (α₁-phase) was successfully synthesized in experiments with excellent ambient stability. However, it is an indirect band gap semiconductor, which hinders its wide application. Here, we systematically studied the stability of the structure and optoelectronic properties of two new α₁-phase monolayers (MoSi₂Sb₄ and WSi₂Sb₄) and a new family of α₂-phase monolayer MSi₂Z₄ (M = Mo, W; Z = P, As, Sb) using first-principles calculations. Our results indicated that all of these monolayer structures showed high structural stability, and the α₂-phase structures are more stable than the α₁-phase structures. Moreover, all of them have direct band gaps with fascinating optical absorption efficiencies ranging from infrared to visible light. Importantly, the high hole mobility (up to 10⁵ cm² V⁻¹ s⁻¹) reveals that these monolayer MSi₂Z₄ will have potential applications in photoelectric devices. In addition, α₂-MoSi₂P₄ possesses a desirable power conversion efficiency of 20.3%. Interestingly, spin–orbit coupling plays a key role in exploring the optoelectronic properties of MSi₂Z₄ ternary compounds. These new ternary monolayer structures can effectively broaden the 2D materials family and provide promising potential candidates for optoelectronic applications.