Nonequilibrium Lattice Dynamics in Photoexcited 2D Perovskites
Nonequilibrium Lattice Dynamics in Photoexcited 2D Perovskites
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DOI：
10.1002/adma.202202709
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发表时间：
2022-10-03
影响因子：
29.4
通讯作者：
Schaller, Richard D.
中科院分区：
文献类型：
--
作者：
Cuthriell, Shelby A.;Panuganti, Shobhana;Schaller, Richard D.
金属卤化物钙钛矿的结构和电物理性质之间的相互作用对于它们在光电子学中的实用性是至关重要的，但是对光激发时的晶格响应的理解有限。在这里，2D钙钛矿丁基碘化铅铵，（BA）（2）PbI 4，和苯乙基碘化铅铵，（PEA）（2）PbI 4，使用超快瞬态X射线衍射作为光激发通量的函数来辨别结构动力学。粉末X射线衍射和时间分辨的光致发光线宽窄超过1纳秒以下的光激发的研究的注量范围内，同时轻微红移的光学带隙。这些观察结果归因于主要由电子-空穴对产生刺激的畸变碘化铅八面体的瞬态弛豫和有序化。c轴在几百皮秒内膨胀到0.37%;在相同的时间尺度下，对a轴和B轴进行采样的反射经历了这种膨胀的十分之一。在（BA）（2）PbI 4中的（110）反射的光激发后外观表明瞬态相变，然而，通过新的单晶XRD，发现反射违反了所报道的Pbca结构中的滑移面条件。静态结构空间群被重新分配为P2（1）2（1）2（1）。由此，排除了非平衡相变。这些发现提供了在激发时在2D钙钛矿中显著的晶格响应的增加的理解。
Interplay between structural and photophysical properties of metal halide perovskites is critical to their utility in optoelectronics, but there is limited understanding of lattice response upon photoexcitation. Here, 2D perovskites butylammonium lead iodide, (BA)(2)PbI4, and phenethylammonium lead iodide, (PEA)(2)PbI4, are investigated using ultrafast transient X-ray diffraction as a function of optical excitation fluence to discern structural dynamics. Both powder X-ray diffraction and time-resolved photoluminescence linewidths narrow over 1 ns following optical excitation for the fluence range studied, concurrent with slight redshifting of the optical bandgaps. These observations are attributed to transient relaxation and ordering of distorted lead iodide octahedra stimulated mainly by electron-hole pair creation. The c axis expands up to 0.37% over hundreds of picoseconds; reflections sampling the a and b axes undergo one tenth of this expansion with the same timescale. Post-photoexcitation appearance of the (110) reflection in (BA)(2)PbI4 would suggest a transient phase transition, however, through new single-crystal XRD, reflections are found that violate glide plane conditions in the reported Pbca structure. The static structure space group is reassigned as P2(1)2(1)2(1). With this, a nonequilibrium phase transition is ruled out. These findings offer increased understanding of remarkable lattice response in 2D perovskites upon excitation.