Aqueous dye-sensitized solar cells: challenges in electrodes and electrolytes design

Dye sensitized solar cells (DSSCs) are not yet commercialized on large scale due to their issues concerning safety and long-term stability. In fact, standard high-efficiency DSSCs are prepared mainly with organic solvent-based liquid electrolytes, i.e. acetonitrile and methoxypropionitrile, and are often characterized by high vapor pressure, toxicity and flammability. In recent years, with the idea of creating efficient, safe, and low-cost DSSCs, the research moved the attention towards alternative solvent-based electrolytes. Above all, DSSCs with water-based electrolytes look like one of the best solution providing reduced costs, nonflammability, better stability, and environmental compatibility. Moreover, the possibility of gelling the liquid solvent into a polymeric matrix can reduce the electrolyte leakage outside the device, increasing the long-term stability. In this contribution, the investigation on a series of iodine/cobalt-based 100% aqueous electrolytes is presented. In parallel, photoanode preparation and sensitization is studied to achieve the best electrode/electrolyte interfaces. Finally, the gelation of aqueous electrolytes with bio-derived polymers is presented, leading to lab-scale devices stable for several months.