<br>通过固态核磁共振波谱完整了解混合钙钛矿材料中的阳离子动力学,Journal of the American Chemical Society

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通过固态核磁共振波谱完整了解混合钙钛矿材料中的阳离子动力学
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2022-12-29 , DOI: 10.1021/jacs.2c10149
Aditya Mishra ₁ , Michael A Hope ₁ , Michael Grätzel ₁ , Lyndon Emsley ₁

Affiliation

有机-无机杂化钙钛矿中的有机阳离子在无机晶格形成的立方八面体空腔内快速旋转，影响光电性能。在这里，我们提供了基于甲脒的钙钛矿和混合阳离子组合物的阳离子动力学的完整定量图，它们是当今钙钛矿太阳能电池中使用最广泛和最有前途的吸收层。我们在魔角旋转下使用² H 和¹⁴ N 四极固态 NMR 弛豫测定法来确定室温下一系列有机阳离子绕每个主轴旋转的活化能 ( E _a ) 和相关时间 (τ _c )。具体来说，我们研究了当前最先进的单阳离子和多阳离子钙钛矿组合物中的甲基铵 (MA ⁺ )、甲脒 (FA ⁺ ) 和胍 (GUA ⁺ ) 阳离子。我们发现 MA ⁺ 、FA ⁺和 GUA ⁺都至少有一个在室温下发生在皮秒时间尺度上的旋转分量，其中 MA ⁺和 GUA ⁺还分别表现出更快和更慢的分量。阳离子动力学取决于无机晶格的对称性，但发现对阳离子取代程度不敏感。特别是，当充分高于相变温度时，FA ⁺旋转在本文研究的所有组合物中都是不变的。我们进一步确定了机械合成的 FA _x MA _{1– x} PbI ₃中 MA ⁺ ² H 的不寻常弛豫机制，该机制被发现是由于物理扩散到顺磁缺陷而产生的。这种阳离子动力学的精确图像将有助于更好地理解有机阳离子与钙钛矿光电特性之间的关系，指导未来更高效的钙钛矿太阳能电池的设计原则。

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A Complete Picture of Cation Dynamics in Hybrid Perovskite Materials from Solid-State NMR Spectroscopy

The organic cations in hybrid organic–inorganic perovskites rotate rapidly inside the cuboctahedral cavities formed by the inorganic lattice, influencing optoelectronic properties. Here, we provide a complete quantitative picture of cation dynamics for formamidinium-based perovskites and mixed-cation compositions, which are the most widely used and promising absorber layers for perovskite solar cells today. We use ²H and ¹⁴N quadrupolar solid-state NMR relaxometry under magic-angle spinning to determine the activation energy (E_a) and correlation time (τ_c) at room temperature for rotation about each principal axis of a series of organic cations. Specifically, we investigate methylammonium (MA⁺), formamidinium (FA⁺), and guanidinium (GUA⁺) cations in current state-of-the-art single- and multi-cation perovskite compositions. We find that MA⁺, FA⁺, and GUA⁺ all have at least one component of rotation that occurs on the picosecond timescale at room temperature, with MA⁺ and GUA⁺ also exhibiting faster and slower components, respectively. The cation dynamics depend on the symmetry of the inorganic lattice but are found to be insensitive to the degree of cation substitution. In particular, the FA⁺ rotation is invariant across all compositions studied here, when sufficiently above the phase transition temperature. We further identify an unusual relaxation mechanism for the ²H of MA⁺ in mechanosynthesized FA_xMA_1–xPbI₃, which was found to result from physical diffusion to paramagnetic defects. This precise picture of cation dynamics will enable better understanding of the relationship between the organic cations and the optoelectronic properties of perovskites, guiding the design principles for more efficient perovskite solar cells in the future.

更新日期：2022-12-29

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