  Capacitance measurements as a function of voltage, frequency and temperature
are useful tools to identify fundamental parameters that affect solar cell
operation. Techniques such as capacitance-voltage (CV), Mott-Schottky analysis
and thermal admittance spectroscopy (TAS) measurements are therefore frequently
employed to obtain relevant parameters of the perovskite absorber layer in
perovskite solar cells. However, state-of-the-art perovskite solar cells employ
thin electron and hole transport layers that improve contact selectivity. These
selective contacts are often quite resistive in nature, which implies that
their capacitances will contribute to the total capacitance and thereby affect
the extraction of the capacitance of the perovskite layer. Based on this
premise, we develop a simple multilayer model that considers the perovskite
solar cell as a series connection of the geometric capacitance of each layer in
parallel with their voltage-dependent resistances. Analysis of this model
yields fundamental limits to the resolution of spatial doping profiles and
minimum values of doping/trap densities, built-in voltages and activation
energies. We observe that most of the experimental
capacitance-voltage-frequency-temperature data, calculated doping/trap
densities and activation energies reported in literature are within these
cut-off values derived, indicating that the capacitance response of the
perovskite solar cell is indeed strongly affected by the capacitance of its
selective contacts.
