Strained induced metallic to semiconductor transitions in 2D Ruddlesden Popper perovskites: A GGA + SOC approach

Based on RP perovskites, we put 2%, 4%, 6%, and 8% biaxial strains on 2D monolayers of phenyl-ammonium tin iodide (PH₂SnI₄) perovskites. Density functional theory (DFT) is used to study the structural distortion, octahedral tilting, band gap tuning, Bader charge analysis, and mechanical stability of the resulting configurations. Band gaps under the effects of compressive strain (Eg1), zero strain (Eg2), and tensile strain (Eg3) follow a decreasing order of Eg₁(1.262 eV) < Eg₂(1.329 eV) < Eg₃(1.331 eV) for 6%-strain. The absence of trap states in energy band gaps and dominant cation and anion contributions at conduction and valence band edges supports the defect tolerance. All the structures analyzed are mechanically stable. The covalently bonded structures are ductile/brittle under tensile/compressive strain, with a prominent stretching mode. Strain improves the optical performance with dielectric constant increased (red-shifted) under compressive strain and reduced (blue-shifted) under compressive strain.