It would be redundant to stress the fact that in the last six years Perovskite Solar Cells (PSCs) have been among the main actors in the new generation photovoltaic scene. However, in spite of some first plans regarding their commercialization, their widespread use for mass production of electrical energy seems a little far, mainly because silicon is a very well established technology for this application and the fierce competition of other inorganic technologies (mostly based on III-V materials). The competitive advantage of Perovskite materials is their ease of processability, but also the possibility to tune the band-gap of the absorbing layer enabling their use as top cells in tandem with other technologies. For these reasons, the easiest and fastest way to the PV market would be helping silicon solar cells to reach higher efficiencies, rather than trying to replace them.

This work is based on the optimization of the IR transmittance of semi-transparent PSCs in order to reduce the parasitic absorption due to charge transporting layers of the perovskite top cell and grant the current matching condition. We explore both the direct and inverted structure testing organic and inorganic charge transporting layers (ranging from TiO₂, SnO₂, NiO₂, MoO₂, CuI, CuSCN to fullerenes and spiro-OMeTAD) preferring solution processing in order to keep manufacturing costs low. We found TCOs to be the most critical layers in terms of IR radiation losses, and therefore performed a study on which would be the best solution as photo-electrode and/or recombination layer in terms of energy level, sheet resistance, process compatibility and optical interference leading to a better IR transmittance (>60%). Regarding the architecture, we developed 2-terminal tandem devices as both, monolithic cells and mechanically stacked tandems. While the monolithic tandem requires process compatibility of the two sub-cells and similar stability of all the involved materials, the second option allows us to drop both these requirements as the two cells can be processed separately and can be replaced when needed, while still resulting in a high open circuit voltage.

The presented study has proved to be successful in enhancing the performance of different stand-alone silicon cells yielding tandem devices with V_oc as high as 1.75 V and Fill Factor around 80%.