Low-dimensional perovskites offer a rare opportunity to investigate lattice dynamics and charge carrier behavior in bulk quantum-confined solids, in addition to them being the leading materials in optoelectronic applications. In particular, zero-dimensional (0D) inorganic perovskites of the Cs₄PbX₆ (X = Cl, Br, or I) kind have crystal structures with isolated lead halide octahedra [PbX₆]^4- surrounded by Cs⁺ cations, allowing the 0D crystals to exhibit the intrinsic properties of an individual octahedron. Using both experimental and theoretical approaches, we studied the electronic and optical properties of the prototypical 0D perovskite Cs₄PbBr₆. Our results underline that this 0D perovskite behaves akin to a molecule, demonstrating low electrical conductivity and mobility as well as large polaron binding energy. Density functional theory calculations and transient absorption measurements of Cs₄PbBr₆ perovskite films reveal the polaron band absorption and strong polaron localization features of the material. A short polaron lifetime of ~2 ps is observed in femtosecond transient absorption experiments, which can be attributed to the fast lattice relaxation of the octahedra and the weak interactions among them.

中文翻译：

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零维钙钛矿的分子行为。

低维钙钛矿除了是光电应用中的领先材料外，还为研究体量子受限固体中的晶格动力学和电荷载流子行为提供了难得的机会。特别是，Cs ₄ PbX ₆（X = Cl，Br或I）类型的零维（0D）无机钙钛矿具有晶体结构，其中孤立的卤化铅八面体[PbX ₆ ] ^4-被Cs ⁺阳离子包围，从而使0D晶体具有单个八面体的固有特性。使用实验和理论方法，我们研究了原型0D钙钛矿Cs ₄ PbBr ₆的电子和光学性质。。我们的结果表明，这种0D钙钛矿的行为类似于分子，表明其低电导率和迁移率以及大的极化子结合能。Cs ₄ PbBr ₆钙钛矿薄膜的密度泛函理论计算和瞬态吸收测量揭示了该材料的极化子带吸收和强极化子局域化特征。在飞秒瞬态吸收实验中观察到了约2 ps的短极化子寿命，这可以归因于八面体的快速晶格弛豫和它们之间的弱相互作用。