Exfoliation of self-assembled 2D organic-inorganic perovskite semiconductors

Ultra-thin flakes of 2D organic-inorganic perovskite (C₆H₉C₂H₄NH₃)₂PbI₄ are produced using micromechanical exfoliation. Mono- and few-layer areas are identified using optical and atomic force microscopy, with an interlayer spacing of 1.6 nm. Refractive indices extracted from the optical spectra reveal a sample thickness dependence due to the charge transfer between organic and inorganic layers. These measurements demonstrate a clear difference in the exciton properties between "bulk" (>15 layers) and very thin (<8 layer) regions as a result of the structural rearrangement of organic molecules around the inorganic sheets.