  Perovskite solar cells (PSC) are shown to behave as coupled ionic-electronic
conductors with strong evidence that the ionic environment moderates both the
rate of electron-hole recombination and the band offsets in planar PSC.
Numerous models have been presented to explain the behavior of perovskite solar
cells, but to date no single model has emerged that can explain both the
frequency and time dependent response of the devices. Here we present a
straightforward coupled ionic-electronic model that can be used to explain the
large amplitude transient behavior and the impedance response of PSC.
