Despite the tremendous interest in halide perovskite solar cells, the structural reasons that cause the all‐inorganic perovskite CsPbI₃ to be unstable at room temperature remain mysterious, especially since many tolerance‐factor‐based approaches predict CsPbI₃ should be stable as a perovskite. Here single‐crystal X‐ray diffraction and X‐ray pair distribution function (PDF) measurements characterize bulk perovskite CsPbI₃ from 100 to 295 K to elucidate its thermodynamic instability. While Cs occupies a single site from 100 to 150 K, it splits between two sites from 175 to 295 K with the second site having a lower effective coordination number, which, along with other structural parameters, suggests that Cs rattles in its coordination polyhedron. PDF measurements reveal that on the length scale of the unit cell, the PbI octahedra concurrently become greatly distorted, with one of the IPbI angles approaching 82° compared to the ideal 90°. The rattling of Cs, low number of CsI contacts, and high degree of octahedral distortion cause the instability of perovskite‐phase CsPbI_3. These results reveal the limitations of tolerance factors in predicting perovskite stability and provide detailed structural information that suggests methods to engineer stable CsPbI₃‐based solar cells.

中文翻译：

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通过依赖于温度的结构分析了解卤化物钙钛矿CsPbI3的不稳定性。

尽管对卤化物钙钛矿太阳能电池有极大的兴趣，但导致全无机钙钛矿CsPbI ₃在室温下不稳定的结构原因仍然是个谜，尤其是因为许多基于耐受因素的方法都预测CsPbI ₃作为钙钛矿应该是稳定的。在此，单晶X射线衍射和X射线对分布函数（PDF）测量表征了钙钛矿块状CsPbI ₃从100到295 K，以阐明其热力学不稳定性。Cs占据100至150 K的单个位点，但在175 K至295 K的两个位点之间分裂，第二个位点的有效配位数较低，这与其他结构参数一起表明Cs在其配位多面体中发出嘎嘎声。PDF测量表明，在单电池的长度尺度中，Pb 我八面体同时变得严重失真，与I的一个铅我的角度接近82°相比，理想的90°。铯，低数目的Cs的晃动我的联系人，以及高程度的八面体失真原因的钙钛矿相的CsPbI不稳定的_3。这些结果揭示了预测钙钛矿稳定性时耐受性因素的局限性，并提供了详细的结构信息，这些结构性信息提出了工程化基于CsPbI ₃的稳定太阳能电池的方法。