Insights into planar CH₃NH₃PbI₃ perovskite solar cells using impedance spectroscopy

Impedance spectroscopy (IS) is emerging as a valuable tool
for the characterization of perovskite-based solar cells (PSCs). However,
earlier reports of the IS response of mesoscopic PSCs have revealed
notable discrepancies, with the interpretation of their spectra having been
generalized to planar PSC devices despite fundamental differences in the
device operation. The present study analyzes the impedance response of
planar PSC devices through the characterization of cells employing a
variety of constituent layers. Distinctive high-frequency and low-frequency
features are observed in IS measurements and are attributed to the charge
recombination across the perovskite/contact interfaces and the dielectric
relaxation in the interfacial regions of the perovskite layer, respectively.
Comparison of the characteristic IS time constants with time-resolved
photoluminescence (TRPL) and open-circuit voltage decay (OCVD)
measurements further substantiates the proposed impedance model. This
work provides an empirical foundation for the interpretation of impedance spectra in planar PSCs, and develops the prospects of IS as a valuable diagnostic tool for future characterization of planar PSC devices.