Metal halide perovskites (MHPs) have attracted increasing research attention given the ease of solution processability with excellent optical absorption and emission qualities. However, effective strategies for engineering the band gap of MHPs to satisfy the requirements of practical applications are difficult to develop. Cubic cesium lead iodide (α-CsPbI₃), a typical MHP with an ideal band gap of 1.73 eV, is an intriguing optoelectric material owing to the approaching Shockley–Queisser limit. Here, we carried out a combination of in situ photoluminescence, absorption, and angle-dispersive synchrotron X-ray diffraction spectra to investigate the pressure-induced optical and structural changes of α-CsPbI₃ nanocrystals (NCs). The α-CsPbI₃ NCs underwent a phase transition from cubic (α) to orthorhombic phase and subsequent amorphization upon further compression. The structural changes with octahedron distortion to accommodate the Jahn–Teller effect were strongly responsible for the optical variation with the increase of pressure. First-principles calculations reveal that the band-gap engineering is governed by orbital interactions within the inorganic Pb–I frame through the structural modification. Our high-pressure studies not only established structure–property relationships at the atomic scale of α-CsPbI₃ NCs, but also provided significant clues in optimizing photovoltaic performance, thus facilitating the design of novel MHPs with increased stimulus-resistant capability.

中文翻译：

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立方铯铯碘化物钙钛矿纳米晶体的减压带隙工程及结构演化

金属卤化物钙钛矿（MHP）吸引了越来越多的研究关注，这是因为其溶液加工性易于实现，并具有出色的光学吸收和发射质量。然而，难以开发出有效的策略来设计MHP的带隙以满足实际应用的要求。立方铯碘化铅（α-CsPbI ₃），一个典型的与MHP 1.73电子伏特的理想的带隙，是由于接近肖克莱-Queisser极限一个有趣的光电材料。在这里，我们在原位光致发光，吸收，和角度色散同步辐射X射线衍射光谱中进行的组合，以调查的压力引起的光学和结构的变化α-CsPbI _3个纳米晶体（NCS）。α-CsPbI ₃NC经历了从立方（α）到正交相的相变，并在进一步压缩后非晶化。八面体畸变的结构变化（以适应Jahn-Teller效应）是随压力增加而引起的光学变化的主要原因。第一性原理计算表明，带隙工程是通过结构修饰在无机Pb–I框架内受到轨道相互作用的支配的。我们的高压研究不仅在α-CsPbI的原子尺度建立结构-性能关系_3个NCS，而且还提供了在优化光伏性能显著线索，从而有利于增加抗刺激能力新颖的MHP的设计。