Electrolytes for dye-sensitized solar cells based on interhalogen ionic salts and liquids

In this paper, we report on the preparation of interhalogen ionic liquids of the general formula [K+]XY2-, where K+=1,3-dialkylimidazolium, 1,2,3-trialkylimidazolium, or N-alkylpyridinium; XY2-=IBr2- or I2Br-. These compounds were characterized in solution and the solid state by NMR, IR, Raman, and mass spectroscopy. The crystal structure of the compound [Me2BuIm]IBr2 (7) shows that the IBr2- anion has a linear Br-I-Br structure. Indications of an equilibrium between different forms of XY2- anions in solution are observed. Interhalogen ionic salts and liquids 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 gamma-butyrolactone, glutaronitrile, or native ionic liquids as solvents, respectively. Moreover, in terms of stability, the cell performance lost 9-14% of the initial performance after 1000 h illumination at 350 W/m2.