Shi Enzheng, Deng Shibin, Yuan Biao, Gao Yao, Yuan Long, Davis Chelsea S, Zemlyanov Dmitry, Yu Yi, Huang Libai, Dou Letian
Davidson School of Chemical Engineering , Purdue University , West Lafayette , Indiana 47907 , United States.
Department of Chemistry , Purdue University , West Lafayette , Indiana 47907 , United States.
ACS Nano. 2019 Feb 26;13(2):1635-1644. doi: 10.1021/acsnano.8b07631. Epub 2019 Feb 7.
Edges of two-dimensional (2D) halide perovskites are found to exhibit unusual properties such as enhanced photoluminescence lifetime and reduced photoluminescence emission energy. Here, we report the formation mechanism and the dynamic nature of edge states on exfoliated 2D halide perovskite thin crystals. In contrast to other 2D materials, the edge states in 2D perovskites are extrinsic and can be triggered by moisture with a concentration as low as ∼0.5 ppm. High-resolution atomic force microscopy and transmission electron microscopy characterizations reveal the width of the low-energy states is ∼40 nm wide. A temperature-dependent photoluminescence study suggests the edge states are a combination of several lower-energy states. Importantly, we demonstrate that the charge carriers on the dynamically formed edge states are not only long-lived but also highly mobile and can be conducted along the edges effectively with high mobilities of 5.4-7.0 cm V s. This work provides significant insights on the origin of the edge states in 2D perovskites and provides routes to manipulate their optical and electrical properties through controlling their edges.
二维（2D）卤化物钙钛矿的边缘表现出异常的特性，如光致发光寿命延长和光致发光发射能量降低。在此，我们报告了剥离的二维卤化物钙钛矿薄晶体上边缘态的形成机制和动态性质。与其他二维材料不同，二维钙钛矿中的边缘态是外在的，并且可以由浓度低至约0.5 ppm的水分触发。高分辨率原子力显微镜和透射电子显微镜表征表明，低能态的宽度约为40 nm。温度依赖的光致发光研究表明，边缘态是几种较低能态的组合。重要的是，我们证明了动态形成的边缘态上的电荷载流子不仅寿命长，而且迁移率高，能够以5.4 - 7.0 cm V s的高迁移率沿边缘有效传导。这项工作为二维钙钛矿中边缘态的起源提供了重要见解，并提供了通过控制其边缘来操纵其光学和电学性质的途径。
