Beyond The First Quadrant: Origin Of The High Frequency Intensity-Modulated Photocurrent/Photovoltage Spectroscopy Response Of Perovskite Solar Cells

The complete interpretation of small perturbation frequency-domain measurements on perovskite solar cells has proven to be challenging. This is particularly true in the case of intensity-modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS) measurements in which the high frequency response is obscured by instrument limitations. Herein, a new experimental methodology capable of accurately resolving the high frequency response-often observable in the second and third quadrants of the complex plane-of a range of perovskite devices is demonstrated. By combining single-frequency IMPS/IMVS measurements, it is able to construct the time dependence of the IMPS/IMVS response of these devices during their initial response to illumination. This reveals significant negative photocurrent/photovoltage signals at high frequency while devices reach steady state, which is in keeping with observations made from comparable time-domain transient measurements. These techniques allow the underlying interfacial recombination and ion migration processes to be assessed, which are not always evident using steady-state measurements. The ability to study and mitigate these processes is vital in optimizing the real-world operation of devices.