Illumination Power-Dependent Electroabsorption of Excitons in a CH₃NH₃PbI₃ Perovskite Film

Electroabsorption (E-A) spectra of methylammonium lead triiodide (MAPbI3) are found to depend on the power density of the illumination light (IL-D) in both tetragonal and orthorhombic phases when the modulation frequency (M-F) of the applied electric field (F) is low. As IL-D increased, the E-A intensity decreased and the shape of the E-A spectra altered from that similar to the second derivative of the exciton absorption band having a Gaussian profile to the one similar to the first derivative, when the M-F of F is low. When the M-F of F is high, E-A spectra were independent of the power density of illumination. Orientational polarization of excitons is considered to be induced by F having a low M-F with strong photoirradiation, following ion migration of MA+ and I- along the applied field direction enhanced by photoirradiation.