Active circuit model of low-frequency behavior in perovskite solar cells
The low-frequency impedance hook in perovskite solar cells (PSC) is a feature that has been frequently associated with the behavior of passive circuits of inductors or negative capacitances. However, if the experimental impedance data do not transform according to the Kramers-Kronig (KK) relations, the system does not fulfill the conditions of linearity, stability, causality and finiteness necessary for validating the impedance measurements and fitting it using passive circuit elements. In this study, we found that the impedance hook in a standard PSC configuration is not compliant with the KK transforms, and as such the system is active and unstable. We propose a model for this low-frequency behavior based on the active gyrator element which consists of two cross-coupled voltage-controlled current sources and has the capability of turning a capacitance into its dual inductive impedance. © 2020 Elsevier B.V.