Dimensional Reduction of Cs₂AgBiBr₆: A 2D Hybrid Double Perovskite with Strong Polarization Sensitivity

Abstract

By dimensional reduction of the 3D motif of Cs2AgBiBr6, a lead‐free 2D hybrid double perovskite, (i‐PA)2CsAgBiBr7 (1, i‐PA=isopentylammonium), was successfully designed. It adopts a quantum‐confined bilayered structure with alternating organic and inorganic sheets. Strikingly, the unique 2D architecture endows it highly anisotropic nature of physical properties, including electric conductivity and optical absorption (the ratio αb/αc=1.9 at 405 nm). Such anisotropy attributes result in the strong polarization‐sensitive responses with large dichroic ratios up to 1.35, being comparable to some 2D inorganic materials. This is the first study on the hybrid double perovskites with strong polarization sensitivity. A crystal device of 1 also exhibits rapid response speed (ca. 200 μs) and excellent stabilities. The family of 2D hybrid double perovskites are promising optoelectronic candidates, and this work paves a new pathway for exploring new green polarization‐sensitive materials.

Room‐Temperature Ferroelectric Material Composed of a Two‐Dimensional Metal Halide Double Perovskite for X‐ray Detection

“…However, these two metal–halide octahedra exhibit the distinct steric geometry. In detail, the AgBr 6 octahedron has a sterically distorted configuration, as revealed by the large deviation of equatorial and axial Ag–Br bond lengths (Figure S2); the BiBr 6 group adopts a nearly regular octahedral geometry (Bi–Br lengths of 2.82–2.88 Å), resembling some other 2D double perovskites that have been reported . Meanwhile, the bilayers of large CPA organic cations reside between two inorganic sheets, with the NH 3 + groups tightly linked to the perovskite frameworks through strong N−H⋅⋅⋅Br hydrogen bonds.…”

“…However,t hese two metal-halide octahedra exhibit the distinct steric geometry.I nd etail, the AgBr 6 octahedron has asterically distorted configuration, as revealed by the large deviation of equatorial and axial Ag-Br bond lengths ( Figure S2);t he BiBr 6 group adopts an early regular octahedral geometry (Bi-Br lengths of 2.82-2.88 ), resembling some other 2D double perovskites that have been reported. [22] Meanwhile,t he bilayers of large CPAo rganic cations reside between two inorganic sheets,w ith the NH 3 + groups tightly linked to the perovskite frameworks through strong NÀH•••Br hydrogen bonds.Asshown in Figure 3a,the C À Nb onds of the adjacent CPA + cations are situated in aparallel arrangement. Such an alignment meets the requirement of crystallographic symmetry for polar order.S ince electric polarization is closely related to the molecular polarity of the organic cations,t he presence of the terminal halogen atom also enhances the molecular asymmetry and dipole moment.…”

3D‐to‐2D Dimensional Reduction for Exploiting a Multilayered Perovskite Ferroelectric toward Polarized‐Light Detection in the Solar‐Blind Ultraviolet Region

“…This work offers an efficient approach for exploring new 2D hybrid perovskite candidates toward future optoelectronic applications. [20a] GeAs, [20b] (i-PA) 2 CsAgBiBr 7 , [21] (HDA) 2 CsPb 2 Br 7 , [22] MAPbI 3 , [3a] (i-BA) 2 PbI 4 , [23] (i-BA) 2 (MA)Pb 2 I 7 [24] )a nd this work.…”

Lead‐Free Halide Double Perovskites: Structure, Luminescence, and Applications

“…A newly synthesized 2D hybrid double‐perovskite SC, (i‐PA) 2 CsAgBiBr 7 (where i‐PA = isopentylammonium) has an approximate absorption ratio ( α b / α c ) up to ≈1.9 at 405 nm, because inorganic layers (i.e., a‐ and b ‐axes) have larger absorbance than the c ‐axis. [ 153 ] The structure distortion is shown in Figure 8 d. This anisotropy resulted in the strong polarization‐sensitive responses with large dichroic ratios up to 1.35, superior than GeSe polarization detectors. Quasi‐two HDPs can also be ferroelectric.…”