Coherent 2D-3D van der Waals perovskite epitaxial heterostructures.

Precise control and a clear understanding of the interfaces between 2D and 3D perovskites remain limited by structural disorder, interfacial defects and poorly defined growth pathways. Here we report a strategy for coherent van der Waals cross-dimensional epitaxy, in which 3D MASnI3 (MA: methylammonium) single crystals are grown directly on 2D (3T)2SnI4 (3T: tri-thiophenylethylammonium) templates. This approach achieves deterministic control over domain orientation, density and coverage, yielding planar heterostructures with atomically sharp and structurally coherent interfaces. Low-dose aberration-corrected transmission electron microscopy and ptychographic imaging resolve the heterointerface in real space, revealing ordered spacer ligands and uniform interfacial passivation. The epitaxial growth tolerates topological defects in the 2D templates, giving rise to spiral heterostructures with pronounced chiroptical responses. The method further extends from microscale domains to macroscopic single-crystal heterostructure thin films, bridging fundamental epitaxy and device-relevant architectures. These heterostructures support efficient charge separation and transport, exhibiting gate-tunable rectification ratios exceeding 106 with robust operational stability. These results define a general route to coherent cross-dimensional epitaxy and establish a versatile platform for scalable perovskite optoelectronics.