Electrolytes for Dye-Sensitized Solar Cells Based on Interhalogen Ionic Salts and Liquids

The authors report on the prepn. of interhalogen ionic liqs. [K+]XY2-, where K+ = 1,3-dialkylimidazolium, 1,2,3-trialkylimidazolium, or N-alkylpyridinium; XY2- = IBr2- or I2Br-. These compds. were characterized in soln. and the solid state by NMR, IR, Raman, and mass spectroscopy. The crystal structure of [Me2BuIm]IBr2 (7) shows that the IBr2- anion has a linear Br-I-Br structure. Indications of an equil. between different forms of XY2- anions in soln. are obsd. Interhalogen ionic salts and liqs. were used as electrolyte components for encapsulated monolithic dye-sensitized solar cells. Overall light-to-electricity conversion efficiencies up to 6.4%, 5.0%, and 2.4% at 1000 W/m2 were achieved by using electrolytes based on interhalogen ionic salts and γ-butyrolactone, glutaronitrile, or native ionic liqs. as solvents, resp. Also, in terms of stability, the cell performance lost 9-14% of the initial performance after 1000 h illumination at 350 W/m2.