Incompletely solvated ionic liquid mixtures as electrolyte solvents for highly stable dye-sensitized solar cells

Abstract

Ionic liquids have been intensively investigated as alternative stable electrolyte solvents for dye-sensitized solar cells (DSCs). A highest overall conversion efficiency of over 8% has been achieved using a ionic-liquid-based electrolyte in combination with an iodide/triiodide redox couple. However, the relatively high viscosities of ionic liquids require higher iodine concentration in the electrolyte due to mass-transport limitations of the triiodide ions. The higher iodine concentration significantly reduces the photovoltaic performance, which normally are lower than those using organic solvent-based electrolytes. Here, the concept of incompletely solvated ionic liquid mixtures (ISILMs) is introduced and represents a conceptually new type of electrolyte solvent for DSCs. It is found that the photovoltaic performance of ISILM-based electrolytes can rival that of organic solvent-based electrolytes. Furthermore, the vapor pressures of ISILMs are found to be considerably lower than that for pure organic solvents. Stability tests show that ISILM-based electrolytes provide highly stable DSCs under light soaking conditions. Thus, ISILM-based electrolytes offer a new platform to develop more efficient and stable DSC devices of relevance to future large-scale applications.