As an alternative to conventional inorganic photovoltaics, dye-sensitized solar cells use an encapsulated nanoparticulate layer in conjunction with a nonvolatile highly conductive ionic liquid. Unfortunately, ionic liquids showing high conversion efficiency when used in these new solar cells are not thermally or chemically robust and can suffer efficiency losses. But researchers at Ecole Polytechnique Fédérale de Lausanne (Lausanne, Switzerland) have used a robust new ionic liquid called 1-ethyl-3 methylimidazolium tetrocyanoborate (EMIB(CN)4) as the ionic liquid for a successful solar cell that achieves 7% energy-conversion efficiency in full sunlight, even after thermal and light aging.
To prove the chemical and thermal robustness of their solar cell, the researchers subjected the devices to heating at 80°C in the dark for 1000 hours, followed by light soaking at 60°C for 1000 hours. After dark heating and light soaking, 90% of the initial photovoltaic efficiency was maintained-the first time such excellent thermal stability has been observed for an ionic liquid electrolyte that exhibits such a high conversion efficiency. Contrary to silicon solar cells whose performance declines with increasing temperature, the dye-sensitized solar-cell devices were only negligibly influenced when increasing the operating temperature from ambient to 60°C. Contact Michael Grätzel at [email protected].Laser Focus World August, 2006