AbstractPerovskite solar cells (PSCs) are one of the most promising photovoltaic technologies. Amongst several challenges, developing and optimizing efficient electron transport layers that can be up‐scaled still remains a massive task. Admittance measurements on metal–oxide–semiconductor (MOS) devices allow to better understand the optoelectronic properties of the interface between perovskite and the charge carrier transport layer. This work discloses a new pathway for a fundamental characterization of the oxide/semiconductor interface in PSCs. Inverted MOS structures, that is, glass/fluorine‐doped tin oxide/tin oxide (SnO₂)/perovskite are fabricated and characterized allowing to perform a comparative study on the optoelectronic characteristics of the interface between the perovskite and sputtered SnO₂. Admittance measurements allow to assess the interface fixed oxide charges (Q_f) and interface traps density (D_it), which are extremely relevant parameters that define interface properties of extraction layers. It is concluded that a 30 nm thick SnO₂ layer without annealing presents an additional recombination mechanism compared to the other studied layers, and a 20 nm thick SnO₂ layer without annealing presents the highest positive Q_f values. Thus, an effective method is shown for the characterization of the charge carrier transport layer/perovskite interface using the analysis performed on perovskite‐based inverted MOS devices.