Multicolor Heterostructures of Two-Dimensional Layered Halide Perovskites that Show Interlayer Energy Transfer

Fabrication of heterostructures using two-dimensional (2D) materials with different bandgaps creates opportunities for exploring new properties and device applications. Ruddlesden-Popper (RP) layered halide perovskites have recently emerged as a new class of solution-processable 2D materials that demonstrate exotic optoelectronic properties. However, heterostructures using 2D halide perovskites have not been achieved. Here, we report a simple solution growth method for making vertically stacked double heterostructures and complex multilayer heterostructures of 2D lead iodide perovskites [(PEA)₂(MA) _n-1Pb _nI_{3 n+1}, PEA = C₆H₅(CH₂)₂NH₃⁺, MA = CH₃NH₃⁺] via van der Waals epitaxy. These heterostructures present atomically sharp interfaces and display distinct photoluminescence that allow fingerprinting the RP phases. Time-resolved photoluminescence measurements reveal internal energy transfer from higher energy bandgap (lower n value) perovskite layers to lower energy bandgap (higher n value) perovskite layers on the time scale of hundreds of picoseconds due to natural type I band alignments. These results offer new strategies to fabricate perovskite-perovskite heterojunctions by taking advantage of surface-bound ligands as spatial barriers to prevent ion migration across the junctions. These heterostructures capable of multicolor emission with high spectral purity are promising for light-emitting applications.