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This work shows 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 respect to the perovskite in the device. We adopt the impedance spectroscopy to enlighten on the modification of the carrier transport mechanisms across the Spiro-OMeTAD/perovskite interface constituting the active part where the main device processes occur. We investigate two interface structures referred to as the direct (or regular, n-i-p) and the inverted (p-i-n) configuration. This work is also intended to further stress on the possible adoption of alternative device structures working with undoped hole transport materials.
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