Octahedral Distortion and Excitonic Behavior of Cs₃Bi₂Br₉ Halide Perovskite at Low Temperature

Abstract

The metal halide ionic octahedron, represented as [MX 6 ] n− (M = metal cation, X = halide anion), serves as the basic structural unit in halide perovskites and plays a crucial role in determining their optoelectronic and chemical properties. Thus, it is possible to correlate the responses of metal halide perovskites to various environmental stimuli with the dynamic behaviors of the [MX 6 ] n− octahedra. In this study, with the temperature-dependent single-crystal X ray diffraction (SCXRD) measurements on Cs 3 Bi 2 Br 9 2D halide perovskites, we can identify two classes of distortions through the lowering of temperature: intraoctahedral distortion, which is the off-centering of Bi 3+ cation within a [BiBr 6 ] 3− octahedron due to the Bi 3+ 6s 2 lone pair electrons, and interoctahedral distortion, which is the collective misalignments among the [BiBr 6 ] 3− building blocks. Free exciton (FE) and self-trapped exciton (STE) models are used to study the relationship between the distortion of octahedra in Cs 3 Bi 2 Br 9 and the corresponding changes in its optoelectronic properties, which transform from dominating blue emission above 100 K to red emission at 4 K. This work provides new insights into the excitonic behaviors of perovskites and suggests a possibility that we can design and rationalize the optical properties of halide perovskites by regulating the environmental stimuli based on the knowledge of behaviors of the individual [MX 6 ] n− building blocks.

Selective oxidative coupling of amines through light‐activated bismuth halide perovskites

“…Figure 1 displays the powder XRD patterns for all synthesized materials Cs 3 Bi 2 (Cl x Br 1‐x ) 9, where x=0 and x=1 corresponds to Cs 3 Bi 2 Br 9 (CBB) and Cs 3 Bi 2 Cl 9 (CBC), respectively. The prominent diffraction peaks of CBB with 2θ of 15.8°, 22.3°, 27.1°, 27.5°, 28.8°, 30.1°, 31.9°, 35.8°, 38.8°, 39.2°, 45.2° and 45.4° are assigned to the crystal planes of (1 0 1), (1 0 2), (0 0 3), (2 0 1), (1 1 2), (1 0 3), (2 0 2), (2 1 1), (1 0 4), (2 1 2), (2 0 4) and (2 2 0), respectively [25] . The diffraction peaks of CBC with 2θ of 23.5°, 30.8°, 33.4°, 36.4°, 38.9°, 41.1°, 47.8°, 53.8°, 59.4°, 64.8°, 74.8°, and 79.7° are assigned to the crystal planes of (4 0 1), (0 4 3), (0 4 4), (3 0 2), (1 5 3), (3 3 1), (0 6 5), (0 6 7), (2 6 7), (1 8 6), (2 5 12) and (1 10 6), respectively [26] .…”

“…The prominent diffraction peaks of CBB with 2θ of 15.8°, 22.3°, 27.1°, 27.5°, 28.8°, 30.1°, 31.9°, 35.8°, 38.8°, 39.2°, 45.2°and 45.4°are assigned to the crystal planes of (1 0 1), (1 0 2), (0 0 3), (2 0 1), (1 1 2), (1 0 3), (2 0 2), (2 1 1), (1 0 4), (2 1 2), (2 0 4) and (2 2 0), respectively. [25] The diffraction peaks of CBC with 2θ of 23.5°, 30.8°, 33.4°, 36.4°, 38.9°, 41.1°, 47.8°, 53.8°, 59.4°, 64.8°, 74.8°, and 79.7°are assigned to the crystal planes of (4 0 1), (0 4 3), (0 4 4), (3 0 2), (1 5 3), (3 3 1), (0 6 5), (0 6 7), (2 6 7), (1 8 6), (2 5 12) and (1 10 6), respectively. [26] According to the XRD patterns, CBB and CBC present high crystallinity and matched quite well with the characteristic reflection peaks (ICSD 001142 (PDF 00-044-0714) (Figure 1a) and (ICSD 2067 (PDF 01-070-0990)) (Figure 1a), respectively.…”

Broadband Achromatic Quarter-Waveplate Using 2D Hybrid Copper Halide Single Crystals

“…To substantiate the presence of out-of-plane mosaicity, we performed SCXRD measurements on three bulk HCH crystals of different thicknesses: thin, middle-thick, and thick samples (crystal images are shown in Figure S13a–c). The utilization of unwarped images, constructed from the raw diffraction frames, facilitated the examination of diffraction features arising from misalignment along the c -axis . Notably, our findings demonstrate that thicker crystals exhibit not only much stronger diffractions but also exhibit significant smearing effects along the ⟨010⟩ axis in the unwarped images generated from the (100) and (001) crystallographic axes (Figure b–d).…”

“…The utilization of unwarped images, constructed from the raw diffraction frames, facilitated the examination of diffraction features arising from misalignment along the c-axis. 25 Notably, our findings demonstrate that thicker crystals exhibit not only much stronger diffractions but also exhibit significant smearing effects along the ⟨010⟩ axis in the unwarped images generated from the (100) and (001) crystallographic axes (Figure 4b−d). Interestingly, this phenomenon is also observable in the (0KL) unwarped image, albeit absent in the (HK0) counterpart (see Figures 4b−d and S13d−f).…”

Ag Intercalation in Layered Cs3Bi2Br9 Perovskite for Enhanced Light Emission with Bound Interlayer Excitons

“…13 While emission from a self-trapped exciton (STE) state formed by an off-centering distortion of [BiBr 6 ] 3− octahedra is present, it is predominantly observed at temperatures below 60 K, where highly distorted [BiBr 6 ] 3− octahedra become immobile. 10,16 The cryogenic conditions needed to enable light emission significantly limit the use of CBB in practical light-emitting applications.…”