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.