Temperature-Dependent Electroabsorption Spectra and Exciton Binding Energy in a Perovskite CH3NH3PbI3 Nanocrystalline Film

Temperature-dependent electroabsorption (E-A) spectra of methylammonium lead tri-iodide (MAPbI3) solid film, which result from the quadratic Stark effect of the exciton absorption band, have been analyzed with an integral method. The change in the electric dipole moment (Δμ) and polarizability (Δα) following exciton absorption was determined at each temperature; the absorption profile was separated into an exciton band and a continuum band caused by a transition from the valence band to the conduction band, and the position and the linewidth of the exciton absorption band were determined at each temperature. As the temperature decreased, a phase transition occurred from a tetragonal phase to an orthorhombic phase; the temperature dependence of Δμ and Δα differed greatly between the two phases. We have evaluated the exciton binding energy (EB) of MAPbI3 polycrystalline film with the following three methods: (1) fitting the temperature-dependent absorption profile; (2) fitting the temperature-dependent linewidth of the exciton absorption profile; and (3) fitting the photoluminescence intensity as a function of temperature. The EB values thus determined for samples fabricated with the same procedure are compared. Our estimated binding energies for an exciton of a MAPbI3 nanocrystalline film are also compared with those reported in the literature.