Two-dimensional (2D)/quasi-2D organic-inorganic halide perovskites are regarded as naturally formed multiple quantum wells with inorganic layers isolated by long organic chains, which exhibit layered structure, large exciton binding energy, strong nonlinear optical effect, tunable bandgap via changing the layer number or chemical composition, improved environmental stability, and excellent optoelectronic properties. The extensive choice of long organic chains endows 2D/quasi-2D perovskites with tunable electron-phonon coupling strength, chirality, or ferroelectricity properties. In particular, the layered nature of 2D/quasi-2D perovskites allows us to exfoliate them to thin plates to integrate with other materials to form heterostructures, the fundamental structural units for optoelectronic devices, which would greatly extend the functionalities in view of the diversity of 2D/quasi-2D perovskites. In this paper, the recent achievements of 2D/quasi-2D perovskite-based heterostructures are reviewed. First, the structure and physical properties of 2D/quasi-2D perovskites are introduced. We then discuss the construction and characterizations of 2D/quasi-2D perovskite-based heterostructures and highlight the prominent optical properties of the constructed heterostructures. Further, the potential applications of 2D/quasi-2D perovskite-based heterostructures in photovoltaic devices, light emitting devices, photodetectors/phototransistors, and valleytronic devices are demonstrated. Finally, we summarize the current challenges and propose further research directions in the field of 2D/quasi-2D perovskite-based heterostructures.

Owing to their excellent optoelectronic properties, halide perovskite is very promising for photodetectors and other optoelectronic devices. Perovskite heterostructures are considered to be the key components for these devices. However, it is challenging to rationally synthesize those heterostructures. Here, we demonstrate that perovskite can be epitaxially grown on PbS by vapor transport, thereby creating an interesting CsPbBr₃-PbS heterostructure. Remarkably, photodetectors based on CsPbBr₃-PbS heterostructures exhibit visible to infrared broadband response with room temperature operation up to 2 μm. The room temperature detectivity higher than 1.0 × 10⁹ Jones was obtained in the 1.8- to 2-μm range. Furthermore, the p-n heterojunction exhibits a clear rectifying characteristic and enables detector to operate at zero-bias. Our study provides fundamentally contributes to establish the epitaxial growth perovskite heterostructures and demonstrate a materials platform for efficient perovskite-based optoelectronic devices.

The optoelectronic performances of the layered materials are strongly dependent on the thickness of the samples due to the surface effect. As the size of the samples decreases to few nanometers, the surface depletion field and surface defect density are prominent arising from the large surface to volume ratio. For instance, thin two-dimensional (2D) organic-inorganic hybrid perovskite microplates usually exhibit a rather low photoluminescence quantum yield (PLQY), owning to the strong surface effect. Here, we report that the PLQY can be enhanced as large as 28 times in (iso-BA)₂PbI₄ (BA = C₄H₉NH₃) 2D perovskite thin microplates encapsulated by graphene, resulting in that the PLQY is more than 18% for the microplate with a thickness of 6.7 nm at 78 K. As the thickness of the 2D perovskite microplate increases, the enhancement is gradually reduced and finally vanishes. This observation is in striking contrast to that in monolayer transition metal dichalcogenides (TMDs), when the PLQY is quenched by covering a layer of graphene due to the efficient charge transfer. The enhancement of PLQY in 2D perovskites can be mainly ascribed to the reduced quantum confined Stark effect (QCSE) due to the reduced surface depletion field after covering graphene flake, resulting in the enhanced radiative recombination efficiency. Our findings provide a cost-effective approach to enhance the luminescence, which may pave the way toward high performance light emitting devices based on 2D perovskites.

Surface depletion field would introduce the depletion region near surface and thus could significantly alter the optical, electronic and optoelectronic properties of the materials, especially low-dimensional materials. Two-dimensional (2D) organic—inorganic hybrid perovskites with van der Waals bonds in the out-of-plane direction are expected to have less influence from the surface depletion field; nevertheless, studies on this remain elusive. Here we report on how the surface depletion field affects the structural phase transition, quantum confinement and Stark effect in 2D (BA)₂PbI₄ perovskite microplates by the thickness-, temperature- and power-dependent photoluminescence (PL) spectroscopy. Power dependent PL studies suggest that high-temperature phase (HTP) and low-temperature phase (LTP) can coexist in a wider temperature range depending on the thickness of the 2D perovskite microplates. With the decrease of the microplate thickness, the structural phase transition temperature first gradually decreases and then increases below 25 nm, in striking contrast to the conventional size dependent structural phase transition. Based on the thickness evolution of the emission peaks for both high-temperature phase and low-temperature phase, the anomalous size dependent phase transition could probably be ascribed to the surface depletion field and the surface energy difference between polymorphs. This explanation was further supported by the temperature dependent PL studies of the suspended microplates and encapsulated microplates with graphene and boron nitride flakes. Along with the thickness dependent phase transition, the emission energies of free excitons for both HTP and LTP with thickness can be ascribed to the surface depletion induced confinement and Stark effect.