LAUSR

Two dimensional (2D) organic–inorganic hybrid perovskites have recently attracted enormous attention due to their higher environmental stability with respect to three-dimensional (3D) perovskites and larger structural tunability. The layered structure relaxes constraints on the dimensions of the organic cations that alternate the inorganic sheets, opening up a large choice on the organics, ultimately enabling the creation of tunable layered perovskites. Here, we report on a series of fluorous cations, varying in size and shape, as building blocks for a new family of fluorous 2D lead-iodide perovskites. These display a large tunability in the optical and dielectric properties depending on the structure of the fluorous cations. Importantly, despite the invariant inorganic framework, the 2D perovskite electronic structure is strongly affected by the cation size. The longer the cation, the smaller the 2D perovskite band gap and the exciton binding energy (reducing from 400 meV down to 130 meV). Such variation...