2 research outputs found
Effects of Perovskite Monovalent Cation Composition on the High and Low Frequency Impedance Response of Efficient Solar Cells
The partial replacement
of methylammonium by formamidinium and
cesium in organolead trihalide materials is of great importance to
improve the performance and stability of photovoltaic solar cells.
However, the effect of multiple cations on the cell functioning and
their electrical characteristics remains to be clarified. By using
the impedance spectroscopy technique, we have investigated the electrical
response to a small ac perturbation applied to solar cells implementing
hybrid perovskites with various compositions, polarized over a large
potential range. The solar cell preparation protocols have been optimized
to reach power conversion efficiencies higher than 17%. The impedance
response has been investigated both under light and in the dark to
discriminate the light sensitive parameters. The spectra have been
carefully analyzed using an <i>ad hoc</i> equivalent circuit,
and the data have been discussed in the light of the existing literature.
The spectra showed no intermediate frequency inductive loop due to
the absence of multistep charge transfer involving surface states.
A large inductive loop is found to be the signature of poorly functioning
solar cells. Except for the high frequency capacitance, which is the
bulk response of perovskite, the other parameters are influenced by
interface and contact phenomena, ionic conductivity and charge accumulations.
The scaling of the low frequency capacitance with the hysteresis amplitude
is clearly stated by our comprehensive study. Moreover, no diffusion
impedance due to the diffusion of ionic species is observed. However,
ion mobility results in a strong effect on recombinations and has
a strong influence on the low frequency impedance response of the
system