Study on gelled aqueous electrolytes for DSSCs with different redox mediators

Dye sensitized solar cells (DSSCs) are a photovoltaic technology able to convert solar light into electricity and have recently achieved conversion efficiencies up to 14%. Nevertheless, DSSCs are not yet commercialized on large scale due to two particular aspects that have been poorly addressed, especially when it is considered that DSSC technology was conceived to be ecofriendly and inspired by photosynthesis. First, the standard electrolyte system is based on volatile organic solvents (e.g., acetonitrile, methoxypropionitrile), also flammable and toxic, which certainly affect the safety requirements when the device is installed. Secondly, the polymer electrolytes that have been introduced as solid or quasi-solid matrices to increase the stability of DSSCs are typically macromolecules derived from the petrochemical industry, which makes the DSSC technology not so much sustainable as it was in the initial intent. Above all, DSSCs with 100% water-based electrolytes appear as the best solution to reduce costs, increase safety, stability, and environmental compatibility, and have recently achieved efficiency up to 6%. Moreover, the idea of gelling the aqueous electrolyte into a low-cost bio-derived polymeric matrix open the possibility to increase long-term stability, preserving DSSCs sustainability. In this contribution, the study on fully aqueous electrolytes gelled with xanthan gum is presented. Thanks to our knowledge and to a multifactorial approach (Design of Experiment, DoE), the effects on DSSCs performances in function of type (I-/I3- vs Co-complex) and concentrations of the redox mediator are evaluated.