Recent progress in layered metal halide perovskites for solar cells, photodetectors, and field-effect transistors.

Metal halide perovskite materials demonstrate immense potential for photovoltaic and electronic applications. In particular, two-dimensional (2D) layered metal halide perovskites have advantages over their 3D counterparts in optoelectronic applications due to their outstanding stability, structural flexibility with a tunable bandgap, and electronic confinement effect. This review article first analyzes the crystallography of different 2D perovskite phases [the Ruddlesden-Popper (RP) phase, the Dion-Jacobson (DJ) phase, and the alternating cations in the interlayer space (ACI) phase] at the molecular level and compares their common electronic properties, such as out-of-plane conductivity, crucial to vertical devices. This paper then critically reviews the recent development of optoelectronic devices, namely solar cells, photodetectors and field effect transistors, based on layered 2D perovskite materials and points out their limitations and potential compared to their 3D counterparts. It also identifies the important application-specific future research directions for different optoelectronic devices providing a comprehensive view guiding new research directions in this field.