Stable, high-efficiency ionic-liquid-based mesoscopic dye-sensitized solar cells

Efficient and stable mesoscopic dye-sensitized solar cells (DSCs) introducing a low-viscosity binary ionic liquid (1-propyl-3-methyl-imidazolium iodide (PMII) and 1-ethyl-3-methyl-imidazolium tetracyanoborate (EMIB(CN) ₄)) electrolyte in combination with a new high-molar-extinction- coefficient ruthenium complex, Ru(2,2′-bipyridine-4,4′-dicarboxylic acid)(4,4′-bis(2-(4-tert-butyloxy -phenyl)ethenyl) -2,2′-bipyridine) (NCS)₂, are demonstrated. The dependence of photovoltaic performance, charge transport and electron lifetime on the composition of the binary ionic-liquid electrolyte with different ratios of PMII/EMIB(CN) ₄ were investigated by electrochemical impedance and photovoltage transient techniques. A photovoltaic conversion efficiency of 7.6% was obtained under simulated full sunlight illumination, which is a record for solvent-free DSCs. These devices exhibit excellent stability at 80°C in the dark or under visible-light soaking at 60°C during 1000 h of accelerated tests.