The PON Best4U project sees the synergistic interaction of different CNR groups belonging to the DSCTM as regards the construction of 4-terminal solar cells / modules in which the bottom cell is a bifacial type heterojunction Si cell and the top cell is a wide band gap semiconductor cell. CNR-IPCF Messina coordinates activities and results with the aim of fabricate efficient DSSCs cells, thanks to the fruitful collaboration with the ISTEC-CNR Faenza that has developed inks based on TiO2 nanoparticles synthesized by CNR-IPCF Bari through different synthetic techniques (colloidal, hydrothermal or sol gel) and ICCOM-CNR Sesto Fiorentino that has optimized a glass-frit sealant. A set of optimized DSSCs and relative materials have been identified for the scaling up of the cell to large area of 1 cm2 to optimize the best compromise between transparency and PCE that is the goldilocks condition for integration in tandem technology in combination Si solar cells.