Bandgap lowering in mixed alloys of Cs₃Bi_2−xSb_xBr₉ perovskite powders

Abstract

Sb–Br perovskite alloys of Cs3Bi2−xSbxBr9 were synthesized and their crystal structures and optical bandgaps characterized by X-ray diffraction and UV-Vis spectroscopy. Electronic structures were calculated using DFT to gain a deeper understanding of the reasons for the variations in the bandgaps.

Band-bowing effects in lead-free double Cs2AgBixSb1−xCl6 perovskites and their anion-exchanged derivatives

“…29 For these compounds, the minimal bandgap was found at Bi : Sb ratio close to 1 : 1 both experimentally and by DFT calculations. 29 For the same phase-pure Cs 3 (Bi x Sb 1− x ) 2 Br 9 alloys, but produced via a mechano-chemical treatment of mixtures of Cs 3 Bi 2 Br 9 and Cs 3 Sb 2 Br 9 , the lowest bandgap was observed at x = 0.2–0.3. 30 The ambiguity in the reported position of the lowest bandgap 29,30 can indicate that a combination of different reasons is responsible for the observed band-bowing effects.…”

“…32 Similar band-bowing effects originating from the non-linear orbital mixing at the band edges on the bandgap of Bi/Sb-based halide alloys were reported for solution-precipitated microcrystalline Cs 3 (Bi x Sb 1Àx ) 2 Br 9 double salts. 29 For these compounds, the minimal bandgap was found at Bi : Sb ratio close to 1 : 1 both experimentally and by DFT calculations. 29 For the same phase-pure Cs 3 (Bi x Sb 1Àx ) 2 Br 9 alloys, but produced via a mechano-chemical treatment of mixtures of Cs 3 Bi 2 Br 9 and Cs 3 Sb 2 Br 9 , the lowest bandgap was observed at x = 0.2-0.3.…”

“…29 For the same phase-pure Cs 3 (Bi x Sb 1− x ) 2 Br 9 alloys, but produced via a mechano-chemical treatment of mixtures of Cs 3 Bi 2 Br 9 and Cs 3 Sb 2 Br 9 , the lowest bandgap was observed at x = 0.2–0.3. 30 The ambiguity in the reported position of the lowest bandgap 29,30 can indicate that a combination of different reasons is responsible for the observed band-bowing effects. These reasons can be both of a chemical nature as assumed in ref.…”

“…Considering the single-phase character of CABSC double perovskites, this behavior can be attributed to the band-bowing effect, often observed for solid-solution semiconductors 24,25 including mixed-metal halide perovskite and perovskite-like compounds. [26][27][28][29][30] The band-bowing in perovskites was attributed to local inhomogeneities in the composition and lattice of the alloyed semiconductor compounds. 26,27 Alternatively, the non-linear bandgap behavior was related to an energy mismatch between atomic orbitals of two different metal cations contributing to the band edges.…”

Lead-free iron-doped Cs3Bi2Br9 perovskite with tunable properties

“…The mixed alloy occupied a smaller bandgap than both the Bi-based and Sb-based perovskites. 38 Amr Elattar et al demonstrated that doping of Cu in Cs 3 Bi 2 Br 9 perovskite significantly reduces the bandgap from 2.56 eV for pristine Cs 3 Bi 2 Br 9 to 1.77 eV at 100% Cu. 23 Mrinmoy Roy et al studied the effect of Pb substitution in Cs 3 Bi 2 Br 9 layered perovskites, finding that the bandgap is reduced from 2.62 eV to 2.23 eV due to the emergence of defect states between the bands.…”