Role of halide anion on exciton binding energy and disorder in hybrid perovskite semiconductors

We present a simplistic approach to determine the electronic-bandgap (E_g) and the exciton binding energy (E_x) of hybrid perovskite (ABX₃ where, A= CH₃NH₃⁺, B = Pb₂⁺, X = Cl, Br or I ion) semiconductor film. In this study, we show the role of the halide anion (X-) on Eg and Ex using a simple room temperature UV-Vis absorption spectrum measurements and model our results using Elliot´s theory of Wannier exciton model to determine the Eg and Ex. We also found that the disorder primarily arises from structure and not composition disorder. This is just a consequence of the fact the Urbach tail, which is a measure of disorder is reasonably independent of the halide anion among three perovskite films.