  Perovskites have proven to be a promising candidate for highly-efficient
solar cells, light-emitting diodes, and X-ray detectors, overcoming limitations
of inorganic semiconductors. However, they are notoriously unstable. The main
reason for this instability is the migration of mobile ions through the device
during operation, as they are mixed ionic-electronic conductors. Here we show
how measuring the capacitance in both the frequency and the time domain can be
used to study ionic dynamics within perovskite-based devices, quantifying
activation energy, diffusion coefficient, sign of charge, concentration, and
the length of the ionic double layer in the vicinity of the interfaces.
Measuring the transient of the capacitance furthermore allows for
distinguishing between ionic and electronic effects.
