Ionic Liquids For Dye-sensitized Solar Cell

The anions and cations composed of ionic liquid is asymmetry, allowing the ions to rotate freely. The unique structure of ionic liquid makes it have many excellent properties. For example, ionic liquids can change their physical, chemical and biological properties by exchanging coordinated anions or cations. The acidity of ionic liquid can be adjusted, showing the acidity of Lewis and Franklin acid. The ionic liquid can be stable in the temperature range of -40 ~ 300℃, and has the characteristics of high thermal stability and chemical stability. Furthermore, ionic liquid has a high conductivity and a chemical window greater than 3V, which can be used in the field of dye-sensitized solar cell. The dye-sensitized solar cells developed in recent years have the advantages of high conversion efficiency, low cost and low production process requirements, which have become a hot research field in recent years. Introducing ionic liquid into dye-sensitized solar cell can solve the above problems and improve the safety and electrical properties of dye-sensitized cells.

Applications:

• Application of ionic liquid in liquid electrolyte: Ionic liquids have important applications in the liquid electrolyte field of dye-sensitized solar cells. For example, the problem of volatilization of organic solvent can be solved by substituting ionic liquid for electrolyte system of all ionic liquid formed by organic solvent. In addition, ionic liquid, as liquid electrolyte of dye-sensitized cell, can also improve the conversion efficiency of the cell. For example, the new imidazole ionic liquids composed of 1-ethyl-3-methyl imidazole and hydrogen fluoride anion have a viscosity of only 419 m Pa• S. Because of the low viscosity, the diffusion of iodide ions is accelerated, which increases the short-circuit current and improves the conversion efficiency of the battery. In order to further improve the conversion efficiency of the battery, organic solvent can be added into the pure ionic liquid electrolyte, which can obviously reduce its viscosity and improve the photoelectric performance of the battery. In addition, studies have shown that it is difficult to achieve both high conversion efficiency and good stability of the battery by relying on a pure ionic liquid as electrolyte, and it will be another focus of future research to mix two or more ionic liquids to make their performance complementary.
• Application of ionic liquid in solid electrolyte: Compared with liquid electrolyte, solid electrolyte has better safety. Ionic liquids have important applications in the design of solid electrolytes. For example, one team reported a dye-sensitized solar cell electrolyte system consisting of an ionic liquid and a low molecular weight gel.

Figure 1. IL-Al₂O₃ nanoparticles used as quasi-solid electrolyte for dye-sensitized solar cell.

Reference

• Chi W S, Roh D K, Kim S J, et al. Hybrid electrolytes prepared from ionic liquid-grafted alumina for high-efficiency quasi-solid-state dye-sensitized solar cells[J]. Nanoscale, 2013, 5(12):5341-5348.