沙特阿卜杜拉国王科技大学Omar F. Mohammed团队实现了二维钙钛矿中光生表面载流子输运的实空间成像。2025年3月18日出版的《光：科学与应用》发表了这项成果。

在层状二维（2D）钙钛矿中，夹在阳离子间隔物之间的无机钙钛矿层形成量子阱（QW）结构，显示出大的激子结合能，阻碍了激子有效解离成自由载流子。这导致了较差的载流子输运特性和低性能的基于光转换的器件，由于实时可访问性的挑战，直接理解底层物理，特别是关于表面态的物理，即使不是不可能，也是极其困难的。

研究组利用了四维扫描超快电子显微镜（4D-SUEM）（这是一种高灵敏度的技术，用于绘制表面载流子扩散图），该扩散与块体中的扩散不同，并对材料性能产生重大影响。他们直接可视化了具有不同无机钙钛矿层厚度（n = 1, 2和3）的2D钙钛矿顶面上的光生载流子在空间和时间维度上的输运。结果表明，对于n=1的情况，光诱导表面载流子扩散速率为~30 cm²·s^-1，对于n= 2的情况，为~180 cm²·s^-1 , n=3时为~470 cm²·s^-1，它们比体积大20倍以上。这是因为与块体相比，电荷载流子传输通道在顶面上的分布要宽得多，这得到了密度泛函理论（DFT）计算的支持。

最后，该发现表明，表面和体载流子扩散行为之间的差异、它们与激子结合能的关系以及二维钙钛矿中的层数直接相关，为通过界面工程提高二维钙钛矿基光电器件的性能提供了有价值的见解。

附：英文原文

Title: Real-space imaging of photo-generated surface carrier transport in 2D perovskites

Author: Wang, Lijie, Wu, Wentao, Yang, Jie, Nughays, Razan, Zhou, Yifan, Ugur, Esma, Zhang, Xi, Shao, Bingyao, Wang, Jian-Xin, Yin, Jun, De Wolf, Stefaan, Bakr, Osman M., Mohammed, Omar F.

Issue&Volume: 2025-03-18

Abstract: In layered two-dimensional (2D) perovskites, the inorganic perovskite layers sandwiched between cation spacers create quantum well (QW) structures, showing large exciton binding energies that hinder the efficient dissociation of excitons into free carriers. This leads to poor carrier transport properties and low-performance light-conversion-based devices, and the direct understanding of the underlying physics, particularly concerning surface states, remains extremely difficult, if not impossible, due to the challenges in real-time accessibility. Here, we utilized four-dimensional scanning ultrafast electron microscopy (4D-SUEM), a highly sensitive technique for mapping surface carrier diffusion that diverges from those in the bulk and substantially affects material properties. We directly visualize photo-generated carrier transport over both spatial and temporal dimensions on the top surface of 2D perovskites with varying inorganic perovskite layer thicknesses (n=1, 2, and 3). The results reveal the photo-induced surface carrier diffusion rates of ~30cm2·s-1 for n=1, ~180cm2·s-1 for n=2, and ~470cm2·s-1 for n=3, which are over 20 times larger than bulk. This is because charge carrier transmission channels have much wider distributions on the top surface compared to the bulk, as supported by the Density Functional Theory (DFT) calculations. Finally, our findings represent the demonstration to directly correlate the discrepancies between surface and bulk carrier diffusion behaviors, their relationship with exciton binding energy, and the number of layers in 2D perovskites, providing valuable insights into enhancing the performance of 2D perovskite-based optoelectronic devices through interface engineering.

DOI: 10.1038/s41377-025-01758-5

Source: https://www.nature.com/articles/s41377-025-01758-5