Extrinsic\nand Dynamic Edge States of Two-Dimensional\nLead Halide Perovskites

Abstract

Edges of two-dimensional\n(2D) halide perovskites are found to exhibit\nunusual properties such as enhanced photoluminescence lifetime and\nreduced photoluminescence emission energy. Here, we report the formation\nmechanism and the dynamic nature of edge states on exfoliated 2D halide\nperovskite thin crystals. In contrast to other 2D materials, the edge\nstates in 2D perovskites are extrinsic and can be triggered by moisture\nwith a concentration as low as ∼0.5 ppm. High-resolution atomic\nforce microscopy and transmission electron microscopy characterizations\nreveal the width of the low-energy states is ∼40 nm wide. A\ntemperature-dependent photoluminescence study suggests the edge states\nare a combination of several lower-energy states. Importantly, we\ndemonstrate that the charge carriers on the dynamically formed edge\nstates are not only long-lived but also highly mobile and can be conducted\nalong the edges effectively with high mobilities of 5.4–7.0\ncm² V^–1 s^–1. This work\nprovides significant insights on the origin of the edge states in\n2D perovskites and provides routes to manipulate their optical and\nelectrical properties through controlling their edges.