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

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.

Rational Design of Molecular Hole-Transporting Materials for Perovskite Solar Cells: Direct versus Inverted Device Configurations.

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.

Multi-Scale-Porosity TiO scaffolds grown by innovative sputtering methods for high throughput hybrid photovoltaics.

We propose an up-scalable, reliable, contamination-free, rod-like TiO 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 TiO layers.

Enhancing dye-sensitized solar cell performances by molecular engineering: highly efficient π-extended organic sensitizers.

This study deals with the synthesis and characterization of two π-extended organic sensitizers (G1 and G2) for applications in dye-sensitized solar cells. The materials are designed with a D-A-π-A structure constituted by i) a triarylamine group as the donor part, ii) a dithienyl-benzothiadiazole chromophore followed by iii) a further ethynylene-thiophene (G1) or ethynylene-benzene (G2) π-spacer and iv) a cyano-acrylic moiety as acceptor and anchoring part. An unusual structural extension of the π-bridge characterizes these structures.