Composition-Dependent Light-Induced Dipole Moment Change in Organometal Halide Perovskites

In this work we investigate the compositional dependence of electric dipole moment in AMX(3) (A: organic; M: metal; X: halogen) perovskite structures using modulation electroabsorption (EA) spectroscopy. By sampling various device structures, we show that the second harmonic EA spectra reflect the intrinsic dipolar property of perovskite films in a layered configuration. A quantitative analysis of the EA spectra of CH3NH3PbI3, NH2CHNH2PbI3, and CH3NH3Sn0.4Pb0.6I3 is provided to compare the impact of the organic and metal cations on the photoinduced response of dipole moment. Based on the EA results, we propose that the A and M cations could both largely affect the dielectric and dipolar properties of the perovskite materials, but through different mechanisms, such as ionic polarization, rotation of molecular dipoles and charge migration. These processes occur at different time scales and thus result in a frequency-dependent dipole response.