Impact of Mobile Ions on Transient Capacitance Measurements of Perovskite Solar Cells

Mitigating the migration of mobile ions within perovskite solar cells is a crucial step on the way to improving their stability. In the past, transient capacitance measurements were applied to extract information about mobile ions, including their activation energy, diffusion coefficient, density, and polarity. However, in this work, we show that the interpretation of capacitance transients is more complex than originally proposed because of the intrinsic nature of the perovskite and the contributions of charge transport layers to the capacitance. Using drift-diffusion simulations and light-intensity-dependent capacitance transient measurements, we show that the direction of capacitance transients is not linked to the polarity of the migrating species. Instead, the direction of the transients is linked to the layer of the cell that dominates capacitance modulation. This work illustrates that transport layers can be crucial for the capacitance and impedance response of perovskite solar cells, and therefore, for characterizing mobile ions in perovskites.