Benzonitrile based electrolytes for best operation of dye sensitized solar cells

Abstract

The beneficial effect of benzonitrile as electrolyte solvent in Dye Sensitized Solar Cells (DSSCs) is demonstrated. The very low vapour pressure of benzonitrile (133 Pa @ 25 °C) ensures long-term stability to the cells and efficiency values were found around 8% for more than 1300 hours. These results were obtained by using commercial P90 titania photoanodes sensitized by N719 dye, i.e., by making use of common and low priced materials. In this way, neither complex dyes nor passivating agents are required to maintain satisfactory efficiencies in a non-volatile electrolyte solvent as 3-methoxypropionitrile, as reported in literature. The results of this work have to be considered an important step towards an easy and economic fabrication of devices with stable performances for commercially convenient periods. Twelve electrolytes were examined: 9 of them had benzonitrile as solvent, different ratios I-/I2 and different ionic liquid iodide salts whereas, for comparison, one electrolyte in acetonitrile and another in 3-methoxypropionitrile were studied. As reference, the redox couple I3−/I− in benzonitrile without additives was also examined. The electrolytes were characterized by specific conductivity vs. temperature, diffusion coefficient of I3− and redox potential of the I3−/I− couple measurements. Efficiency, dark current and IPCE of DSSCs were determined for each electrolyte.