Exploring the Stability of Mixed-Halide Vacancy-Ordered Quadruple Perovskites

Abstract

The structural and optical properties of the halide substitutions of Br − and I − into Cs 4 M II M III 2 Cl 12 (M II = Cd 2+ , Mn 2+ ; M III = Bi 3+ , Sb 3+ ) have been investigated. All compositions adopt the ⟨111⟩ layered vacancy-ordered quadruple perovskite structure with R3̅ m space group symmetry. Through incremental halide substitution reactions, we show that significant bromide incorporation is possible (>25% for Cd 2+ -containing structures). The larger halide ions (Br − or I − ) preferentially occupy the anion sites adjacent to the cation-vacancy layer. In those compositions where M II is Cd 2+ , incorporation of bromide ions leads to substantial M II /vacancy antisite disorder, which is accompanied by a more even distribution of bromide substitution over the two chemically distinct anion sites. The Cs 4 CdM III 2 Cl 12 compounds can incorporate over twice the amount of bromide as analogous Mn 2+ -containing compounds, with a maximum of 29(2)% bromide substitution found for Cs 4 CdSb 2 Cl 12 . Iodide incorporation is more limited, with a maximum of ∼6% halide substitution for Cs 4 CdBi 2 Cl 12 . The incorporation of the heavier, less electronegative Br − and I − ions results in a red shift of the onset of optical absorption in a Vegard's Law type fashion. The effect is largest for Cs 4 CdBi 2 Cl 12−z X z , where the absorption onset shifts from 3.20(1) eV to 2.99(1) eV as the composition changes from Cs 4 CdBi 2 Cl 12 to Cs 4 CdBi 2 Cl 8.9 Br 3.1 . As discussed in the paper, these results offer some insights into the factors that stabilize the vacancy-ordered quadruple perovskite structure.

Hybrid Organic–Inorganic Halide Derivatives of the 2H Hexagonal Perovskite Structure

“…We hypothesize that this trend can be traced back to differences in anion polarizability. The ∼90° M–X–M bond angles seen in the 2H structure allow for the electron cloud around the halide ion to be polarized toward the inorganic cations, whereas the linear M–X–M bonds of the cubic structure do not permit polarization (in a dipolar sense) because the point symmetry of the halide site (4/ mmm ) possesses an inversion center. − This effect may also help to explain why the cubic structure is stabilized to higher values of t for quaternary double perovskites than it is for ternary perovskites. When the two octahedral cations become different, it lowers the site symmetry of the halide site to 4 mm , which does not have an inversion center.…”

Lanthanide doping enabled multimodal luminescence in layered lead-free double perovskite Cs4MnBi2Cl12

“…The Mn 2+ ions are completely substituted by Cd 2+ to form Cs 4 CdBi 2 Cl 12 with the same crystal structure. 38 Then Yb 3+ ions are incorporated into the Cs 4 CdBi 2 Cl 12 crystal to study the NIR emission of Yb 3+ (Fig. S10, ESI †).…”

“…First, the Bi 3+ ions are excited to the 1 P 1 state, followed by a fast relaxation to the 3 P 0 level. After that, two possible energy transfer processes occur: one is that the excitation energy of Bi 3+ can directly transfer to the neighboring Yb 3+ , resulting in the NIR emission; the other one is that the excitation energy absorbed by Bi 3+ transfers to Mn 2+ through a resonant Dexter-type energy transfer process, 38 followed by the subsequent energy transfer of excited Mn 2+ ions to the 2 F 5/2 state of Yb 3+ , which also contributes to the NIR emission of Yb 3+ , though this is a minor process compared with the direct energy transfer of Bi 3+ to Yb 3+ . Although the detailed energy transfer mechanism between Mn 2+ and Yb 3+ needs further investigation, the PLQY data (Table S4, ESI†) show that the quantum-cutting effect should hardly be involved in this dopant energy transfer and relaxation processes due to the insufficient energy input from Mn 2+ .…”

Theoretical Prediction of Mixed-Valence Layered Halide Perovskites Cs4M(IV)M(II)2X12 (M = Ge, Sn; X = Cl, Br)

“…The mixed halogen effect of Cs 4 M(II)M(III) 2 X 12 on the optoelectronic properties has been investigated in previous experiments. 49 They found that the larger halide ions (Br − or I − ) preferentially occupy the anion sites adjacent to the cation-vacancy layer. Thus, here the mixed halogen was also considered in our work.…”

“…Therefore, in the following sections, Cs 4 M­(IV)­M­(II) 2 X 12 with R -3 m and C 2/ m symmetry were selected to be discussed. The mixed halogen effect of Cs 4 M­(II)­M­(III) 2 X 12 on the optoelectronic properties has been investigated in previous experiments . They found that the larger halide ions (Br – or I – ) preferentially occupy the anion sites adjacent to the cation-vacancy layer.…”