(Invited) Application of Impedance Spectroscopy for Perovskite Solar Cells

Perovskite solar cells (PSCs) have reached over 20% efficiency. However, there is still room for improvement of the reproducibility of the solar cell performance in the PSCs. Also, PSCs still have unknown properties such as a hysteresis of I-V curve, effects of the porous layers in the electron transporting layer, and effects of aging. Characterization of the PSCs is essential to understand the electronic properties of the materials and their interfaces in PSCs. Currently, the general architecture for an efficient PSC with n–i–p configuration can be summarized as follows: transparent conductive oxide (TCO) as the electron-collecting layer / n-type semiconductor for the electron-transporting layer (ETL) / perovskite as the intrinsic material / p-type semiconductor for the hole-transporting layer (HTL) / metal as the hole-collecting layer. The photovoltaic performances of PSCs without an ETL or HTL are inferior to those with the standard PSC structure, indicating the important role of charge selection and transportation in the ETL and HTL. Impedance spectroscopy is powerful method for measurement of the resistance components and the capacitance in the electronics devices and is often used for characterizations of the PSCs. However, impedance spectra in PSCs are mostly used for supporting the presumption in the results without verification of the spectra assignment. On the other hand, there are reports to verify the impedance spectra of PSCs with the complexity equivalent circuits. Interpretation of the impedance spectra for PSCs with simple equivalent circuits is significant for the accurate characterization of PSC as a general method. In this research, we prepared the model PSCs including the layer with different thickness and measured the impedance spectra of the model PSCs to understand the correspondence between the PSC architecture and spectra.