论文标题
通过拉曼光谱和第一原理计算的二维杂化牵引力钙钛矿中铵弯曲振动的表征
Characterization of the Ammonium Bending Vibrations in Two-Dimensional Hybrid Lead-Halide Perovskites from Raman Spectroscopy and First-Principles Calculations
论文作者
论文摘要
二维杂交有机 - 无机钙钛矿（2D HOIP）的便利合成和电子性能使这些自组装系统成为重要类别的能量材料类别。这些材料的基本构建基块包括通常由甲基二面的二叶甲基甲基类和有机分子组成的无机晶格框架。了解无机层和有机层之间的耦合是揭示2D HOIP的电子特性如何与其结构相关的关键。在这项工作中，我们利用拉曼光谱测量和第一原理计算来表征四个2D HOIP的拉曼活性模式：己酰胺二铅碘化物[（HA）$ _ 2 $ _ 2 $ _ 2 $ _ PBI $ _4 $，ha = c $ _6 $ _6 $ _6 $ _ H $ H $ _ {13} $ nh $ nh $ nh $ _3^+$ _3^+$ _3^+$ _ HEXYLANN [（ha）$ _ 2 $ pbbr $ _4 $]，丁基铵铅碘化物[（ba）$ _ 2 $ _ 2 $ pbi $ _4 $，ba = c $ _4 $ _4 $ _9 $ _9 $ _9 $ nh $ _3^+$]和苯甲酰胺含量iodide [（bna）$ _ 2 $ _2 $ pbi $ _4 = c $ _6 $ h $ _5 $ ch $ _2 $ nh $ _3^+$]。我们专注于1400-1600 cm $^{ - 1} $范围，其中分子成分的拉曼强度是最强的，并分配了在实验中观察到的主要峰值作为铵弯曲振动。我们基于局部密度近似和基于VDW-DF-CX函数的冷冻 - phonon方法的密度功能扰动理论的组合，以找到实验性和计算的拉曼光谱之间的定量一致性。此外，通过将分离的分子阳离子的振动光谱与接近六角形簇的振动光谱进行比较，我们显示了无机晶格框架如何调节有机阳离子的振动特性。我们得出的结论是，拉曼活性铵弯曲模式的性质可以有效探测2D HOIP中无机晶格框架的局部微观结构。
The facile synthesis and electronic properties of two-dimensional hybrid organic-inorganic perovskites (2D HOIPs) make these self-assembled systems an important class of energy materials. The basic building blocks of these materials include inorganic lattice frameworks that often consist of lead-halide octahedra and organic molecules possessing ammonium functional groups. Understanding the coupling between the inorganic and organic layers is key to unraveling how the electronic properties of 2D HOIPs relate to their structures. In this work, we leverage Raman spectroscopy measurements and first-principles calculations to characterize the Raman-active modes in four 2D HOIPs: hexylammonium lead iodide [(HA)$_2$PbI$_4$, HA = C$_6$H$_{13}$NH$_3^+$], hexylammonium lead bromide [(HA)$_2$PbBr$_4$], butylammonium lead iodide [(BA)$_2$PbI$_4$, BA = C$_4$H$_9$NH$_3^+$], and benzylammonium lead iodide [(BNA)$_2$PbI$_4$, BNA = C$_6$H$_5$CH$_2$NH$_3^+$]. We focus on the 1400-1600 cm$^{-1}$ range where the Raman intensity of the molecular constituents is the strongest, and assign the major peaks observed in experiments as ammonium bending vibrations. We employ a combination of density functional perturbation theory based on the local density approximation and the frozen-phonon approach based on the vdw-DF-cx functional to find quantitative agreement between experimental and calculated Raman spectra. Furthermore, by comparing the vibrational spectra of isolated molecular cations with those near lead-halide clusters, we show how the inorganic lattice framework modulates the vibrational properties of the organic cations. We conclude that the properties of the Raman-active ammonium bending modes could effectively probe the local microscopic structure of the inorganic lattice framework in 2D HOIPs.
