Ion-mediated hopping electrode polarization model for impedance spectra of CH₃NH₃PbI₃

Methylammonium lead iodide (CH₃NH₃PbI₃) is one of the most attractive materials for optoelectronic applications, and it is the most typical absorber in perovskite solar cells, which are unprecedentedly successful devices in terms of power conversion efficiency. In this work, the conductivity and capacitance spectra of symmetrically contacted Au/CH₃NH₃PbI₃/Au thick pellets are measured via impedance spectroscopy at different temperatures in dark equilibrium. The experimental conductivity spectra are parameterized and showed to follow the formalism of hopping DC conductivity in the CH₃NH₃PbI₃ bulk. The presence of several regimes for the general Jonscher's “universal” conductivity–frequency response is highlighted and associated with the ionic–electronic overlapping conductivities. For the capacitance spectra, the general features of electrode polarization capacitance at the CH₃NH₃PbI₃/Au interfaces are identified but yet are found to be in disagreement with some trends of classical ionic conductivity models, unable to separate different contributions. Accordingly, an analytical model is proposed accounting for hopping processes where the low frequency activation energy is split into ionic and electronic components. Our parameterizations and analytical model discern between the bulk/interface and ionic/electronic phenomena and estimate the multiple activation energies in this hybrid halide perovskite.