Extrinsic and Dynamic Edge States of Two-Dimensional Lead Halide Perovskites

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
cm2 V–1 s–1. 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.