Application of Ionic Liquids in Solar Cells and Batteries: A Review

Ionic liquids are an environmentally friendly media and have been utilized in many research fields. Ionic liquids have many advantageous properties as follows: (1) Vapor pressure is extremely low for many ionic liquids; (2) Thermal and chemical stability are very high; (3) Excellent solubility in both inorganic and organic chemicals; (4) Polarity and phase behavior are changeable; (5) Excellent electrochemical properties; (6) Low melting point. Many ionic liquids are liquid at temperature as low as -60 °C. This property is useful to utilize in the cold climates; (7) Designable functional groups. Due to the excellent physical and chemical properties, ionic liquids can be utilized as novel and promising materials in renewable energy generation and energy storage processes. For example, ionic liquids can be utilized as novel electrolytes in solar cells, including dye-sensitized solar cells, quantum dotorganic solar cells, polymer solar cells, and thin films solar cells. Ionic liquids electrolytes have good thermal stability and high conductivity compared to conventional electrolytes. In addition, ionic liquids can be utilized in energy storage processes. Ionic liquids are excellent electrolytes for batteries, including Li-ion battery, Li battery, Li-oxygen battery, Li-air battery, Li-sulfur battery, Al-ion battery, Alair battery, Na secondary battery, and Na-ion batteries. Moreover, ionic liquids can be utilized as electrolyte additives in batteries, such as Li-ion battery and lead acid battery, to improve the efficiency of the original electrolytes. The recent development of utilizing ionic liquids as electrolytes in solar cells and batteries, as well as electrolyte additives in batteries, is introduced in this review.