The present study involved an investigation on the reasoning behind the dependence of the perovskite solar cells photovoltaic efficiencies on the relative position of the undoped spiro-OMeTAD hole-transport material with respect to the perovskite in the device. We adopted impedance spectroscopy to investigate the modification of the carrier transport mechanisms across the spiro-OMeTAD/perovskite interface constituting the active part where the main device processes occur. We investigated two interface structures, referred to as the direct (or regular, n-i-p) and the inverted (p-i-n) configuration. This work also intended to further stress the possible adoption of alternative device structures working with undoped hole-transport materials.