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 (ABX
₃
where, A= CH
₃
NH
₃
⁺
, B = Pb
₂
⁺
, 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.