Band gap tailoring with octahedral distortion and bader charge analysis for 2D-Ruddlesden–Popper monolayer tin halide perovskites

Intercalation of large organic spacer cations with inorganic layers of octahedral metal halide cages in 2D-Ruddlesden–Popper (RP) monolayer perovskites (R–NH3)₂A_n−1B_nX_3n+1 by using a rational design approach has shown structural versatility and energetic stability. A systematic theoretical investigation of the structural, electronic, and mechanical properties was conducted with and without spin-orbit coupling (SOC) under the influence of a range of organic monovalent spacer cations [R–NH₃]⁺ with different inorganic halide anions. This resulted in 12 compositions. Lattice distortion and octahedral tilting provided gradient band gaps that displayed a good linear relationship with equatorial Sn–X–Sn angles in debt of larger halide anions. By fixing halide ions, larger spacer cations reduce the band gap further. The halides function as acceptors, whereas Sn and N function as donors. Intermingled N-atoms of spacer cations incorporate additional charges to axial halide ions of [SnX₆]^4- with state-of-the-art features of defect tolerance, quantum and dielectric confinement, low effective masses, and high mobility.