The Impact of Ion Migration on the Electro-Optic Effect in Hybrid Organic-Inorganic Perovskites

Electro-optic (EO) modulation allows the conversion of electrical signals to optical pulses and is widely employed in telecommunications and chip-to-chip interconnects. Recently, hybrid organic-inorganic perovskites (HOIPs) have been explored as candidates for EO modulators. To improve the EO performance, it is envisioned that halide doping will lower the symmetry of the crystal, enhancing spontaneous polarization. However, mixed halide perovskites are often associated with ion migration, which may impact their EO properties. Thus, the influence of ion migration on the EO efficiency is investigated using Br-doped Dion-Jacobson quasi-2D HOIPs, (4AMP)(MA)Pb-2(Br-x/I-1-(x))(7) (4AMP = 4-(aminomethyl)piperidinium, MA = methylammonium). While density functional theory predicts a greater spontaneous polarization for the Br-doped sample, it is found that experimental results are affected by ion migration. The EO coefficient of the Br/I mixed sample is 95 pm V-1 at 1 kHz (approximate to 50x higher than the undoped sample), but the response falls off rapidly with frequency. This frequency dependence is correlated with impedance spectroscopy, showing that the large EO signal results from ion migration. This study shows that ion migration impacts the EO analysis of mixed halide perovskites and must be considered in future EO studies.