Liquid-Phase van der Waals Epitaxy of a Few-Layer and Unit-Cell Thick Ruddlesden-Popper Halide Perovskite.

2D Ruddlesden-Popper (RP) halide perovskites with natural multiple quantum well structures are an ideal platform to integrate into vertical heterostructures, which may introduce plentiful intriguing optoelectronic properties that are not accessible in a single bulk crystal. Here, we report liquid-phase van der Waals epitaxy of a 2D RP hybrid perovskite (4,4-DFPD) 2 PbI 4 (4,4-DFPD is 4,4-difluoropiperidinium) on muscovite mica and fabricate a series of perovskite-perovskite vertical heterostructures by integrating it with a second 2D RP perovskite R-NPB [NPB = 1-(1-naphthyl)ethylammonium lead bromide] sheets. The grown (4,4-DFPD) 2 PbI 4 nanobelt array can be multiple layers to unit-cell thin and are crystallographically aligned on the mica substrate. An interlayer photo emission in this R-NPB/(4,4-DFPD) 2 PbI 4 heterostructure with a lifetime of about 25 ns at 120 K has been revealed. Our demonstration of epitaxial (4,4-DFPD) 2 PbI 4 array grown on mica via liquid-phase van der Waals epitaxy provides a paradigm to prepare orderly distributed 2D RP hybrid perovskites for further integration into multiple heterostructures. The discovery of a new interlayer emission in the R-NPB/(4,4-DFPD) 2 PbI 4 heterostructure enriches the basic understanding of interlayer charge transition in halide perovskite systems.