Quantifying mobile ions in perovskite-based devices with capacitance measurements

Metal halide perovskites have proven to be a promising candidate for highly-efficient solar cells and light-emitting diodes. 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. The understanding of ion migration is crucial for the fabrication of stable and efficient perovskite-based devices. We will show how measuring the temperature-dependent capacitance in both the frequency and the time domain can be used to study ionic dynamics within perovskite devices, quantifying activation energy, diffusion coefficient, sign of charge, and concentration of mobile ions. Both A-site and B-site doping has shown positive effects on both the performance and the stability of perovskite-based devices. However, the origins of the increase in operational stability are not well understood. We will show how capacitance measurements help to understand stability improvements using potassium-passivated perovskite solar cells and perovskite light-emitting diodes with manganese substitution as examples.