Tribology-driven modulation of piezoelectricity in 2D CdS bilayers: a first-principles investigation

The pronounced electronegativity difference and exceptional non-centrosymmetricity of two-dimensional (2D) cadmium sulfide (CdS) offer an exceptional piezoelectric effect, positioning it as a promising material for next-generation energy-harvesting devices. This study examines the piezoelectric properties of 2D CdS bilayers driven by tribological effects and assesses their feasibility for nano energy harvesting applications. Two types of tribological effects, namely in-plane sliding motion and out-of-plane compression, are applied to a CdS bilayer to investigate its piezoelectric properties, including potential energy, polarization deviations, charge density, shear strength, induced voltage, and power density. The results indicate that in-plane sliding, which transitions the bilayer structure from an A-B to an A-A stacking pattern, leads to a significant increase in out-of-plane piezoelectricity. Upon vertical compression, we find that the range of maximal energy corrugation is 724-1365 meV, and the range of shear strength is 49.79-99.20 GPa. Additionally, due to vertical compression, an induced voltage of 0.35 V is found for bilayer 2D CdS. Finally, a compressive-sliding motion-based nanogenerator model is proposed for a 2D CdS bilayer structure that can engender an output power density of up to 51.72 mW cm^-2. These outcomes pave the way for new opportunities in nanoenergy extraction from the tribo-piezoelectric effect of CdS structures, advancing the development of wearable electronics, self-powered devices, and wireless technologies.