Water-based electrolytes in hybrid solar cells: from liquid to gel formulations

Dye sensitized solar cells (DSSCs) with high performances have been fabricated mainly with organic solvent-based liquid electrolytes. However, these solvents not only have high vapor pressure, but they are often toxic and flammable. In the last few years, the idea of moving towards a water-based system clearly emerged. DSSCs fabricated with water-based electrolytes may offer reduced costs, non-flammability and environmental compatibility, but the presence of water in the cell may reduce the long term stability as well as the photovoltaic performance. For this reason, in recent years, an increasing number of research articles has been published in this direction and new dyes, electrodes and electrolyte components are continuously proposed. In this work, the study of different truly aqueous electrolytes is presented and a chemometric approach, useful to investigate and optimize their efficiency and stability, is effectively demonstrated. A few curious and anomalous behaviors observed in the literature and in our laboratories are investigated for this class of electrolytes. Moreover the development of a series of novel aqueous gel electrolytes based on natural polymers is also discussed as well as their interesting photovoltaic characteristics.