TiO2 nanotubes as flexible photoanode for back-illuminated dye-sensitized solar cells with hemi-squaraine organic dye and iodine-free transparent electrolyte

Back-illuminated Dye-Sensitized Solar Cells (DSSCs) have been fabricated employing TiO2 nanotube (NT) arrays grown on a flexible Ti foil as a working electrode, an organic hemi-squaraine-based dye (CT1) as sensitizer, and a iodine-free transparent redox mediator (both in liquid and quasi-solid configuration) as electrolyte. The structural and morphological properties of the photoanodes and the obtained electrical performances on the final DSSC devices reaching conversion efficiencies values up to 2% are presented and discussed. The feasibility of a back-illuminated solar cell without corrosive and light-absorbing iodine-based electrolytes, metal-laden sensitizers and nanoparticles-based anodes has been demonstrated. Our work opens the way toward low-cost, non-polluting and flexible cells, proposing for the first time a solution for overcoming the limit of a low light harvesting in back-illuminated DSSCs.