Design of novel SnIX (X=Br/Cl) Janus layers: Electronic, optical, photocatalytic properties, as well as defect and strain engineering

Abstract

We design SnIX (X=Br/Cl) Janus layers (JLs) using first principles-based calculations. The overall stability of the designed structures is validated using the formation energy, phonon spectra, elastic constants as well as ab initio molecular dynamics (AIMD) simulations. The calculated phase diagrams suggest suitable chemical conditions for the experimental realization of the JL. The as-designed JLs show electron mobility in the zig-zag direction which is about one order higher than previously reported for 2D materials. The exciton binding energy calculated using the Bethe Salpeter equation (BSE) method is 0.60 and 0.97 eV for SnIBr and SnCl respectively. The band alignment (BA), calculated using generalised gradient approximation(GGA), Heyd-Scuseria- Ernzerhof (HSE) and Green’s function based GW approximations straddle the water redox potentials and favour overall water splitting (OWS). The reaction rate determining steps (RDS) for hydro-gen and oxygen evolution reaction (HER and OER) are calculated from Gibbs free energy (GFE) changes. For light-on condition it is found that the RDS of HER is smallest for pH=0 and can be further reduced below zero by defect (I monovacancy) and compressive (biaxial or uniaxial) strain engineering. On the other hand, the RDS data for OER are smallest for pH=14 and can be further diminished by tensile strain. Under compressive strain and at medium pH values there are optimum conditions for OWS (i.e. for both HER and OER) with RDS close to zero eV. Also, we could achieve solar to hydrogen efficiency of 15.71% in SnIBr and 12.62% in SnICl by applying biaxial tensile strain.