Revealing the role of thiocyanate anion in layered hybrid halide perovskite (CH₃NH₃)₂Pb(SCN)₂I₂

The effect of the SCN^- ion on the structural, electronic, optical, and mechanical properties of the layered (MA)₂Pb(SCN)₂I₂ (MA=CH₃NH₃ ⁺) perovskite is investigated by using first-principles calculations. Our results suggest that the introduction of SCN^- ions at the apical positions gives rise to shorter Pb-S bond lengths, more distorted octahedra, and more hydrogen bonds, which have important effects on the electronic, optical, mechanical, and piezoelectric properties in (MA)₂Pb(SCN)₂I₂. Furthermore, a strong relativistic Rashba splitting is induced due to the breaking of the inversion symmetry, which helps to suppress the carrier recombination and enhance the carrier lifetime. The analysis of mechanical properties reveals that the incorporation of SCN^- ions is beneficial to strengthen Young's modulus of the perovskite materials and it enhances the piezoelectric properties. Our investigation suggests that doping SCN^- ions into the perovskite materials could be a promising strategy to improve the stability and mechanical properties of organic-inorganic hybrid halide perovskite compounds.