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.