Role of direct and inverted undoped Spiro-OMeTAD – perovskite architectures in determining solar cells performances: an investigation via electrical impedance spectroscopy

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.