Metal halide perovskites (MHPs) have emerged as highly promising candidates for the next generation of photonics and optoelectronic devices, owing to their prominent optical and excitonic properties, as well as the convenience of fabrication. Particularly, ultrathin two-dimensional (2D) MHPs, which are generally prepared by exfoliation, solution growth, and chemical vapor deposition method, have attracted dramatically increasing attentions owing to their combined features of ultrathin 2D morphology and superior performance of MHPs. Despite the growing interest in ultrathin 2D MHPs, there is currently a lack of a comprehensive and systematic overview of the distinct advantages offered by each growth method for producing these materials. This review critically assesses the preliminary studies on the materials design and preparation of ultrathin MHPs. Furthermore, it explores heterostructures based on ultrathin MHPs and offers insights into the challenges and opportunities that lie ahead for this enticing class of 2D materials.

Heterogeneous stackings of two-dimensional (2D) semiconductors and halide perovskites have attracted much attention owing to their respective superior optoelectronic properties. Black phosphorus (BP), as a unique 2D member with narrow bandgap, high mobility, and strong anisotropy, has never been combined with 2D layered perovskites. Herein, we construct a new BP-based van der Waals heterostructure combing with 2D chiral hybrid perovskite (i.e., (MBA)₂PbI₄) for promoting the performance and enriching the functionalities of BP. A series of BP characteristics, including carrier mobility, photoresponsivity, and polarization sensitivity, are synergistically enhanced when interfacing with (MBA)₂PbI₄. For instance, the photodetector responsivity and photogain of BP in heterostructures are boosted by almost one order of magnitude with respect to BP alone, which is more obvious under excitation above the bandgap of perovskite. This is because the interfacing perovskite provides an inflow of numerous photogenerated carriers to BP, to reinforce the charge carrier transfer, separation, and transport processes. Additionally, the ability of both linearly and circularly polarized photodetection can be integrated into the BP/(MBA)₂PbI₄ heterostructure. Our work sheds new insight on the heterostructure assembly for promising optoelectronic applications within 2D materials and perovskite families.