Quaternary ammonium polyiodides as ionic liquid/soft solid electrolytes in dye-sensitized solar cells

Four new quaternary ammonium iodides, (Me2Pe2N)I, (Me2Hex2N)I, (Et2Pe2N)I and (Et2Hex2N)I, were synthesized and studied as electrolytes in dye-sensitized solar cells. All compounds were solids at room temperature. Influence of varying amounts of elemental iodine and the effect of tert-butylpyridine (TBP) on the performance of the cell was also studied. Addition of iodine lowered the melting points of the resulting polyiodides. From the ammonium iodides only (Me2Hex2N)I:I2 (10:1) was liquid at the room temperature and the others were soft solids. Under illumination from a halogen lamp source at 10 mW cm−2 intensity, the highest power conversion efficiency of 2.4% was obtained with the (Me2Hex2N)I:I2 (10:1) liquid electrolyte containing TBP, which may be compared to an efficiency of 5.4% obtained from similar cells with traditional 3-methoxypropionitrile based electrolyte tested under identical conditions. The best efficiency with soft solid electrolyte, (Et2Hex2N)I:I2 (10:1) with TBP, was 2.3%.