The polarizability of organic-metal-halide perovskites has become a topic of great interest. In june 2014 we reported (Photoinduced Giant Dielectric Constant in Lead Halide Perovskite Solar Cells, Emilio J. Juarez-Perez et al. ) that the dielectric constant of CH3NH3PbI3 becomes enormous at very low frequencies, and the effect becomes strongly amplified when the perovskite is illuminated. This phenomenon is intriguing and very important as it indicates that there are strong changes of ionic-electronic structure when the perovskite is photoexcited. However, in general large dielectric constant can also be produced by macrosocopic polarization at interfaces. Therefore it is very important to combine capacitance measurements with determination of microscopic dipolar moments in different conditions. The paper by Ni Zhao et al presents a good contribution to this discussion by determination of photoinduced dipole moments by electroabsorption technique.
Light-Induced Dipole Moment Change in Organometal Halide Perovskites3 01 2015
J. Phys. Chem. C, 2015
In this work we investigate the compositional dependence of electric dipole moment in AMX3(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.