As a member of the bismuth iodide family compounds, Cs₃Bi₂I₉ perovskite shows potential applications in photovoltaic devices and radiation detectors, due to the absence of toxic lead and its high air and moisture stability. In this work, we report Cs₃Bi₂I₉ bulk crystals grown by a low temperature solvent volatilized crystallization method. The morphology of the single crystals exhibits a well symmetric hexagonal shape, with a layered structure along the [00l] direction. Three defect related transitions (iodine substituting bismuth (I_Bi) to the valence band maximum (VBM), the conduction band minimum (CBM) to caesium substituting bismuth (Cs_Bi^1−/2−), and the CBM to caesium substituting iodine (Cs_I^1+/2+)) are identified in 10 K photoluminescence spectra, with dissociation energies of 47.87 meV, 45.28 meV, and 52.01 meV, respectively. The anisotropic resistivities along the [00l] and [l00] directions are compared, with values of 11.08 GΩ cm and 0.77 GΩ cm, respectively, which is attributed to the difference of carrier mobility. This is further certified by the first principles calculations, which demonstrate that the effective masses along the [00l] and [l00] directions are 3.22m_e (electrons)/2.14m_e (holes) and 0.327m_e (electrons)/0.946m_e (holes), respectively. The Cs₃Bi₂I₉ device exhibits fast photoresponse to optical light, with an on–off ratio of ∼24 along [l00], which is fifteen times higher than that along [00l]. This photoelectric anisotropy dictates the potential applications in photovoltaic devices and radiation detectors.

中文翻译：

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低温溶液法生长的 无铅卤化物钙钛矿Cs ₃ Bi ₂ I ₉块状晶体

作为碘化铋家族化合物的成员，Cs ₃ Bi ₂ I ₉钙钛矿由于无毒铅及其高的空气和湿气稳定性而显示出在光伏设备和辐射探测器中的潜在应用。在这项工作中，我们报告了通过低温溶剂挥发结晶法生长的Cs ₃ Bi ₂ I ₉块状晶体。单个晶体的形态表现出良好对称六边形形状，与沿着[00层状结构升]方向。三种与缺陷相关的转变（碘取代铋（I _Bi）至价带最大值（VBM），确定了铯取代铋的导带最小值（CBM）（Cs _Bi ^{1- / 2-}），以及铯取代碘的CBM的导带最小值（Cs _I ^{1 + / 2 +}））在10 K的光致发光光谱中，解离能分别为47.87 meV，45.28 meV和52.01 meV。沿着[00所述的各向异性的电阻率升]和[升00]方向相比，具有的分别11.08GΩ厘米和0.77GΩ厘米，这归因于载流子迁移的差值。这由第一原理计算进一步证明，该计算表明沿[00 l ]和[ l 00]方向的有效质量为3.22。m _e（电子）/2.14 m _e（孔）和0.327 m _e（电子）/0.946 m _e（孔）。Cs ₃ Bi ₂ I ₉器件对光表现出快速的光响应，沿[ l 00]的开关比率约为24 ，比沿[00 l ]的开关比率高15倍。这种光电各向异性决定了在光电器件和辐射探测器中的潜在应用。