Activating the Screened Thermoelectric and Photocatalytic Water-Splitting Potential in Janus Sn₂XY (X ≠ Y = Te, Se, and S) Monolayers via Doping and Strain Engineering

A recent theoretical report discovered that the relatively new Janus γ-Sn₂XY (X ≠ Y = Te, Se, and S) monolayers possess enhanced piezoelectricity performance, with a reported near Shockley-Queisser limit band gap (E_g) and high carrier mobility. Inspired by these positive traits, further detailed studies on their untested green energy conversion properties are warranted. Herein, the unexplored thermoelectric and photocatalytic properties of these materials have been extensively investigated using first-principles density functional theory, Boltzmann transport theory, and Bethe-Salpeter method, respectively. Their stability from energy, mechanical, and thermal up to the 800 K viewpoint was, respectively, confirmed via the cohesive energies, ab initio molecular dynamics, and elastic tensor coefficients analyses. Attributed to their intrinsically low thermal conductivity, large Seebeck coefficients, and high electrical conductivity, the n-doped Sn₂TeSe and Sn₂TeS monolayers exhibit a combined desirable figure of merit of ∼0.9 and ultrahigh power factor above 0.06 W m^-1 K^-2 from 300 to 700 K, rendering them a promising candidate for efficient thermoelectric energy conversion. Findings also reveal that these monolayers have rather significant visible region optical absorption spectra. Particularly, based on its HSE06-calculated band edges and free energy studies, Sn₂TeS under minimal tensile strain displays favorable photocatalytic water-splitting ability with a solar-to-hydrogen conversion efficiency of 23.8%. Graphical analysis also indicates the feasibility of CO₂ and lesser N₂ reduction by these monolayers.