Capacitance spectroscopy of thin-film formamidinium lead iodide based perovskite solar cells

This work concerns the interpretation of capacitance spectroscopy results in perovskite-based solar cells. Based on the deep level transient spectroscopy and admittance spectroscopy results, we present arguments that the observable signals in perovskite-based solar cells come from anion migration rather than being a response from deep trap energy levels. The ion migration parameters, such as activation energy and ion concentration, are calculated and compared to theoretical values for different migration paths of ions in perovskites. Those parameters evolve with time, reflecting in the degradation of the cells, which we propose to link with a change in the anion migration path in perovskite. •The same signal is observed in DLTS and admittance spectroscopy.•Its activation energy is in the 0.3 eV–0.5 eV range and decays with time.•Time constants and the presence of large capacitance transients at +1 V point into the diffusion related origin of the signals.•Low activation energy, DLTS sign, comparison with other experiments and theoretical calculations point into anion diffusion.•The observed, dominating signal correlates with the increased shunt of the device.