Two-dimensional Janus XAu2Y (X=S, Se; Y=Se, Te, X≠Y) monolayers: potential multifunctional materials for photocatalytic and piezoelectric applications

Two-dimensional Janus XAu2Y (X = S, Se; Y=Se, Te, X≠Y) family is systematically investigated as multifunctional materials for photocatalytic water splitting and piezoelectric applications using first-principles calculations. The asymmetric Janus configurations induce an internal electric field, boosting charge separation and overcoming the typical 1.23 eV band gap threshold for photocatalysts. The high stability of the XAu2Y monolayer has been identified through the analysis of phonon spectra, molecular dynamics simulations, and mechanical properties. The band edge position of the XAu2Y family straddles the redox potential of water, achieving a solar hydrogen (STH) conversion efficiency of up to 28.9 %. Its excellent electron mobility (1738–3384 cm2/V/s) and high anisotropy between electron and hole mobility can effectively suppress carrier recombination; meanwhile, the strong absorption ability of XAu2Y towards visible light ensures the efficient utilization of solar energy. Notably, their built-in electric field also endows them with excellent piezoelectric properties and with out-of-plane piezoelectric coefficients surpassing many Janus counterparts. Strain engineering has shown that the photocatalytic and piezoelectric performances of XAu2Y can still be maintained under biaxial strain. The combination of high STH efficiency and excellent piezoelectric response makes the Janus XAu2Y monolayer a potential multifunctional material for energy conversion technology.