“…Previous reports show that Cs 3 Bi 2 I 9 and MA 3 Bi 2 I 9 crystallize in hexagonal structure (P6 3 /mmc) [
35–37 ] with the 0D motive of bi‐octahedra, while Cs 3 Bi 2 Br 9 crystallizes in trigonal (P
m1) [
38,39 ] and Cs 3 Bi 2 Cl 9 in either orthorhombic (Pnma) [
40,41 ] or trigonal (P
1c) [
42 ] crystal systems (space groups), with the 2D motive of BiBr 6 and BiCl 6 octahedra, respectively. Due to the reduced dimensionality, A 3 Bi 2 X 9 perovskites have relatively large band gap (1.94–3.02 eV) [
36,41,42 ] and extremely low ionic migration.…”