Limited information of impedance spectroscopy about electronic diffusion transport: The case of perovskite solar cells

Impedance Spectroscopy (IS) has proven to be a powerful tool for the extraction of significant electronic parameters in a wide variety of electrochemical systems, such as solar cells or electrochemical cells. However, this has not been the case with perovskite solar cells, which have the particular ionic-electronic combined transport that complicates the interpretation of experimental results due to an overlapping of different phenomena with similar characteristic frequencies. Therefore, the diffusion of electrons is indistinguishable on IS, and there appears the need to use other small perturbation experimental techniques. Here, we show that voltage-modulated measurements do not provide the same information as light-modulated techniques. We investigate the responses of perovskite solar cells to IS, Intensity-Modulated Photocurrent Spectroscopy (IMPS) and Intensity-Modulated Photovoltage Spectroscopy (IMVS). We find that the perturbations by light instead of voltage can uncover the electronic transport from other phenomena, resulting in a loop in the high-frequency region of the complex planes of the IMPS and IMVS spectra. The calculated responses are endorsed by the experimental data that reproduce the expected high frequency loops. Finally, we discuss the requirement to use a combination of small perturbation techniques for successful estimation of diffusion parameters of perovskite solar cells.