Impacts of cation ordering on bandgap dispersion of double perovskites

Double perovskites using dual metal cations are promising candidates for Pb-free perovskites. This study shows that the electronic structures of double perovskites (A₂B⁺B³⁺X₆) can be significantly modulated by cation ordering changes. The bandgap of Cs₂AgBiCl₆ can be affected by changing octahedron alignments, and even zero gap states can be realized for the 2-dimensional BiCl₆ (AgCl₆) configuration. It is presented that different types of B⁺/B³⁺-site orderings in double perovskites could be the origin of bandgap dispersion. Comparative studies on the various compositions show that, among B⁺/B³⁺ cations, Tl/Bi could be promising for the suppression of ordering variation.