Anisotropic dielectric behavior of layered perovskite-like Cs3Bi2I9 crystals in the terahertz region
Anisotropic dielectric behavior of layered perovskite-like Cs3Bi2I9 crystals in the terahertz region
复制标题
太赫兹区层状钙钛矿型Cs3Bi2I9晶体的各向异性介电行为
DOI：
10.1039/d0cp04485g
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发表时间：
2020-11-14
影响因子：
3.3
通讯作者：
Xu, Yadong
中科院分区：
文献类型：
--
作者：
Sun, Qihao;Yang, Wenhui;Xu, Yadong
三元金属卤化物钙钛矿由于具有可调谐的晶体结构和合适的带隙，在光电领域的应用逐渐受到重视。无铅Cs3Bi2I9钙钛矿具有0D层状结构，含有分子[Bi2I9]（3-）二聚体，具有明显的光学和电学各向异性。利用太赫兹时域光谱（THz-TDS）对Cs3Bi2I9晶体的各向异性特性进行了评价；同时，利用密度泛函微扰理论（DFPT）证实了声子振动对太赫兹传输的影响。因此，由于在0.2 ~ 0.9太赫兹范围内的高透射率，使用太赫兹- tds估计折射率和消光系数。观察到Cs3Bi2I9晶体的各向异性折射率，（100）平面（CBI(100)）为3.2 ~ 3.7,（001）平面（CBI(001)）为2.8 ~ 3.2。此外，利用Lorentz模型提取了Cs3Bi2I9的介电常数，其中静态介电常数和高频介电常数的各向异性表现明显。这些各向异性行为是由偶极矩决定的，这归因于[Bi2I9]（3-）二聚体的各向异性堆积密度。该研究具有重要意义，对Cs3Bi2I9的各向异性光电特性有了更深入的了解，有助于金属卤化物钙钛矿在光电子学领域的发展。
The ternary metal halide perovskites have gradually attracted attention for application in the optoelectronic field, owing to their tunable crystal structure and appropriate bandgap. Lead free Cs3Bi2I9 perovskite, with a 0D layered structure containing molecular [Bi2I9](3-) dimers, exhibits prominent optical and electrical anisotropies. Here, the anisotropic properties of the Cs3Bi2I9 crystals were evaluated using terahertz time-domain spectroscopy (THz-TDS); meanwhile, the effect of phonon vibration on the THz transmission was confirmed using density functional perturbation theory (DFPT). Accordingly, the refractive index and extinction coefficient are estimated using THz-TDS, thanks to the high transmission in the range of 0.2-0.9 THz. The anisotropic refractive index was observed for the Cs3Bi2I9 crystals, and was found to be 3.2-3.7 for the (100) plane (CBI(100)) in contrast to 2.8-3.2 for the (001) plane (CBI(001)). Furthermore, the Lorentz model was employed to extract the dielectric constant of Cs3Bi2I9, in which anisotropy is obviously indicated by the static dielectric constant and the high-frequency dielectric constant. These anisotropic behaviors are determined by the dipole moment, which is attributed to the anisotropic packing density of [Bi2I9](3-) dimers. This study is significant and provides a deeper insight into the anisotropic photoelectric properties of Cs3Bi2I9, thus contributing to the development of metal halide perovskites in the field of optoelectronics.