Two-Dimensional Janus Nanostructures M₂AB (M = Si, Ge, Sn, A/B = N, P, As) for Piezoelectric Power Generation

Two-dimensional (2D) Janus structures, as a newly derived form of 2D materials, have recently attracted great attention due to their structural symmetry breaking along with a piezoelectric effect and potential applications in nanoscale sensors, surface acoustic waves, and energy harvesters. To date, 2D Janus materials mainly appear in the IV-VI and III-V systems but are scarce involving the IV-V elements. Hereby, utilizing first-principles structure prediction, a stable IV-V-V family of 2D Janus structure 1T-M(2)AB (M = Si, Ge, Sn, A/B = N, P, As) was proposed. Their electronic, elastic, and piezoelectric properties are systematically investigated and compared. The calculated piezoelectric coefficient results reveal that the 1T-Sn2NP exhibits superior piezoelectric performance with a high in-plane piezoelectric constant (-8.07 pm/V), beyond many known 2D piezoelectric materials. Three independent factors of charge density distribution, vertical mirror asymmetry, and electrostatic potential gradients were assessed, which can well account for the piezoelectric characteristics of 1T-M(2)AB. This work not only demonstrates the potential applications of 2D Janus 1T-M(2)AB monolayer in piezoelectric devices but also enriches the family of 2D Janus structures.