  The hybrid perovskite CH3NH3PbX3 (X= Cl, Br, I) is a promising material for
developing novel optoelectronic devices. Owing to the intrinsic non-layer
structure, it remains challenging to synthesize molecularly thin CH3NH3PbX3
with large size. Here, we report a low-cost and highly efficient fabrication
route to obtain large-scale single-crystalline 2D CH3NH3PbX3 perovskites on a
mica substrate via liquid epitaxy. The 2D perovskite is characterized as 8 nm
in thickness and hundreds of micrometers in lateral size. First-principles
calculations suggest the strong potassium-halogen interactions at the
perovskite/mica interface lower the interface energy of perovskites, driving
their fast in-plane growth. Spectroscopic investigations reveal 2D CH3NH3PbBr3
possess small exciton binding energy of 30 meV, allowing a superior
visible-light photodetector with a photoresponsivity of 126 A/W and a bandwidth
exceeded 80 kHz. These features demonstrate that liquid epitaxy is a bottom-up
approach to fabricate the non-layer structured 2D perovskites, which offer a
new material platform for the device applications and fundamental
investigations.
