Due to a still limited understanding of the reasons making 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (Spiro-OMeTAD) the state-of-the-art hole-transporting material (HTM) for emerging photovoltaic applications, the molecular tailoring of organic components for perovskite solar cells (PSCs) lacks in solid design criteria. Charge delocalization in radical cationic states can undoubtedly be considered as one of the essential prerequisites for an HTM, but this aspect has been investigated to a relatively minor extent. In marked contrast with the 3-D structure of Spiro-OMeTAD, truxene-based HTMs Trux1 and Trux2 have been employed for the first time in PSCs fabricated with a direct (n-i-p) or inverted (p-i-n) architecture, exhibiting a peculiar behavior with respect to the referential HTM. Notwithstanding the efficient hole extraction from the perovskite layer exhibited by Trux1 and Trux2 in direct configuration devices, their photovoltaic performances were detrimentally affected by their poor hole transport. Conversely, an outstanding improvement of the photovoltaic performances in dopant-free inverted configuration devices compared to Spiro-OMeTAD was recorded, ascribable to the use of thinner HTM layers. The rationalization of the photovoltaic performances exhibited by different configuration devices discussed in this paper can provide new and unexpected prospects for engineering the interface between the active layer of perovskite-based solar cells and the hole transporters.

We propose an up-scalable, reliable, contamination-free, rod-like TiO2 material grown by a new method based on sputtering deposition concepts which offers a multi-scale porosity, namely: an intra-rods nano-porosity (1–5 nm) arising from the Thornton’s conditions and an extra-rods meso-porosity (10–50 nm) originating from the spatial separation of the Titanium and Oxygen sources combined with a grazing Ti flux. The procedure is simple, since it does not require any template layer to trigger the nano-structuring, and versatile, since porosity and layer thickness can be easily tuned; it is empowered by the lack of contaminations/solvents and by the structural stability of the material (at least) up to 500 °C. Our material gains porosity, stability and infiltration capability superior if compared to conventionally sputtered TiO2 layers. Its competition level with chemically synthesized reference counterparts is doubly demonstrated: in Dye Sensitized Solar Cells, by the infiltration and chemisorption of N-719 dye (∼1 × 1020 molecules/cm3); and in Perovskite Solar Cells, by the capillary infiltration of solution processed CH3NH3PbI3 which allowed reaching efficiency of 11.7%. Based on the demonstrated attitude of the material to be functionalized, its surface activity could be differently tailored on other molecules or gas species or liquids to enlarge the range of application in different fields.