Effect of a redox electrolyte in mixed solvents on the photovoltaic performance of a dye-sensitized solar cell

The effect of the iodide/triiodide redox electrolyte in various organic solvents on the photoelectrochemical properties of bis(tetrabutylammonium) cis-bis(thiocyanato)bis(4-carboxy-2,2′-bipyridine-4′-carboxylato)ruthenium(II)-sensitized nanocrystalline TiO2 solar cells was studied. Solvents with large donor numbers dramatically enhanced the open-circuit voltage (Voc), but usually reduced the short-circuit photocurrent density (Jsc). For a mixed solvent of tetrahydrofuran (THF) and acetonitrile, Voc increased and the fill factor decreased with increasing THF concentration, but Jsc remained relatively constant. As the partial charge of the N or O atom of the solvent molecule increased, Voc increased, but Jsc was unchanged up to a certain value of the partial charge (for THF, −0.46). For cells using 0.3 M 4-tert-butylpyridine and 20 vol% THF in the electrolyte, a short-circuit photocurrent density of 18.23 mA cm−2, an open-circuit voltage of 0.73 V, a fill factor of 0.73, and an overall conversion efficiency of 9.74% were obtained.