The effects of device degradation on perovskite solar cell impedance spectra: insights from a drift-diffusion model

Adrift-diffusion model is used to investigate the effect of device degradation on the impedance response of a perovskite solar cell (PSC). Modifications are made to the open-source drift-diffusion software IonMonger to replicate the effects of a realistic lab protocol on an unstable PSC. These are modelled using a time-dependent degradation factor that simulates increases in the bulk SRH recombination rate. It is shown that degradation occurring during measurement can induce loops in the Nyquist plot and that there are subtle, but clear, distinctions between these loops and those that occur in non-degrading cells. Furthermore, impedance spectroscopy is demonstrated to be remarkably sensitive to changes in device power conversion efficiency. A PCE decrease of 0.18% during the experiment is sufficient to induce a visible loop in the Nyquist plot and a drop of 0.06% between successive measurements causes noticeable changes to the spectrum.