Sci. Adv. 5, eaau3241 (2019)

Owing to their enhanced photostability, two-dimensional (2D) halide perovskites are posed to impact the field of perovskite optoelectronics. In 2D perovskites that form a typical multiple quantum well (MQW) structure, the presence of strong quantum confinement effects largely affects the charge transport and photophysics of the material system. To provide much needed further insights into these phenomena, Wang et al. investigate the edges of 2D perovskite heterolayers.

The researchers synthesize single crystal MQW perovskite thin films and characterize their top layers by conducting atomic force microscopy. While the bulk terrace region of the samples shows insulating properties, an unexpectedly strong current is detected along the contour of the layer edges. The increase in current at the sharp layer edges can be attributed to the free charge carriers residing at the edge states. Scanning electron microscopy, confocal Raman and photoluminescence measurements confirm that the observed feature cannot be ascribed to chemical compounds at the edges or surface charge accumulation and instead is intrinsic in nature. Furthermore, the current is not sensitive to illumination — it changes polarity depending on the scan direction and is characterized by a metal-like carrier density.