Lead-free iron-doped Cs3Bi2Br9 perovskite with tunable properties

The bandgap of lead-free, non-toxic Cs 3 Bi 2 Br 9 perovskite material is reduced from 2.54 eV to 1.78 eV by changing the crystal structure to Cs 3 Bi 2− x Fe x Br 9 , Cs 2 Bi 1− x Fe x Br 5 , and CsFeBr 4 , depending on the varying Fe doping concentrations.