Optical absorption and photoluminescence properties of Pb(I,Br)-based two-dimensional layered Perovskite

The influence of (C6H5C2H4NH3)(2)Pb(BrxI4-x) concentration on the formation of mixed crystals and optical properties of these materials was investigated. Thin films of microcrystalline (C6H5C2H4NH3)(2)Pb(BrxI4-x) were prepared by the spin-coating method using different concentrations of DMF solutions. Macroscopic inhomogeneity of the composition due to the precipitation of undesired phases could be suppressed by controlling the (C6H5C2H4NH3)(2)Pb(BrxI4-x) concentration. These films showed strong exciton absorption with large (250-430 meV) binding energy due to both the quantum and dielectric confinement effect. Replacing I with Br made it possible to shift the exciton band to the blue region, however, photoluminescence from the mixed crystals gradually broadened with increasing the Br content.