Ionic-Liquid Solar Cells

Chemists in China and Switzerland have designed a robust and efficient dye-sensitized solar cell (DSC) based on a solvent-free mixture of three imidazolium compounds (Nat. Mater., DOI: 10.1038/nmat2224). Each of the substances is a solid under ambient conditions. But when mixed in equimolar ratios, they form a eutectic melt, thereby providing a three-component, room-temperature ionic liquid.

The potential for low cost and flexibility makes DSCs attractive alternatives to conventional solar energy conversion devices based on crystalline silicon. A key limitation of most DSC designs is the need for electrolytes dissolved in organic solvents, which can evaporate and permeate cell components. Researchers have had success sidestepping the evaporation and leakage problems by using solvent-free ionic liquids, but most of these compounds decompose under prolonged exposure to sunlight.

Now, a team led by Peng Wang of the Institute of Applied Chemistry, in Changchun, China, and Michael Grätzel of the Swiss Federal Institute of Technology, in Lausanne, formed a novel ionic liquid by blending 1-ethyl-3-methylimidazolium iodide with the dimethyl and allyl-methyl analogs. Compared with other ionic liquid DSCs, solar cells based on the new substance are more resistant to decomposition and exhibit 1–2% higher solar conversion efficiencies.