Characterization of Mobile Ions in Perovskite Solar Cells with Capacitance and Current Measurements by Approximating Drift-Diffusion Simulations

The migration of mobile ions is one of the leading causes of the degradation of perovskite solar cells. However, quantifying mobile ions in complete perovskite solar cells is challenging due to the complex device stacks and the impact of charge transport layers on the measurement techniques. Here we develop a simple and openly accessible that approximates drift-diffusion simulations. The step model is based on the expression of the charge density in the ionic and electronic accumulation and depletion layers as step functions. We can then accurately determine the impact of mobile ions on the dc potential distribution of perovskite solar cells. Furthermore, we can simulate electrical measurement techniques commonly used to quantify mobile ions: capacitance transient, current transient, and capacitance-frequency measurements. By validating the step model with drift-diffusion simulations, we show that an accurate extraction of ion density, diffusion coefficient, and activation energy is possible in an accessible range. We finally apply the step model developed to estimate the ionic conductivity and activation energy of perovskite solar cells.