Janus materials have garnered significant attention due to their vertical polarization properties stemming from their asymmetric structure, while the pursuit of materials with exceptional piezoelectric performance for effective electromechanical conversion remains challenging. In this study, the Janus MoXSiN2 (X═S, Se, and Te) structure is proposed and subjected to first-principles calculations to explore its piezoelectric characteristics and it reveals in-plane piezoelectric strain coefficients d11 of 1.86, 2.26, and 4.11 pm·V–1 for the MoSSiN2, MoSeSiN2 and MoTeSiN2 monolayers, respectively. The broken mirror symmetry leads to out-of-plane piezoelectric strain coefficients d31 of MoSSiN2, MoSeSiN2 and MoTeSiN2 monolayers are 0.17, 0.29, and 0.48 pm·V–1, respectively. The exceptional elastic flexibility resulting from weak covalent bonds is crucial to the remarkable piezoelectric properties of the MoTeSiN2 monolayer. The significant impact of a strong inherent electric field should be emphasized as a key factor contributing to the substantial d31 value observed in the MoTeSiN2 monolayer. The correlation between electronegativity difference ratios and piezoelectric strain coefficients further underscores the findings of this study. This research lays the theoretical foundation for the potential application of Janus MoXSiN2 (X═S, Se, and Te) monolayers in flexible nanoscale piezoelectric devices.

Emergence of In-Plane and Out-of-Plane Piezoelectricity in Flexible Janus MoXSiN2 (X═S, Se, and Te) Monolayers