New functional triethoxysilanes as iodide sources for dye-sensitized solar cells

Three new triethoxysilanes bearing quaternary ammonium alkyl iodides are reported, N,N,N-triethyl-3-(triethoxysilyl)propan-1-aminium iodide 1, N,N,N-triheptyl-3-(triethoxysilyl)propan-1-aminium iodide 2 and N,N,N-tridodecyl-3-(triethoxysilyl)propan-1-aminium iodide 3. H-1 and C-13 NMR spectroscopy and electrospray mass spectrometry were used to confirm the synthesis of pure products. Electrolytes based on these ionic liquids were developed and their performance in dye-sensitized solar cells (DSSCs) evaluated. The electrolytes incorporated 1 and 2 (in 30-60wt%) as iodide sources together with I-2 (0.08 M), 0.1 M guanidinium thiocyanate and 0.5 M tert-butylpyridine in acetonitrile (AN); and 12 (0:15 M) and N-methylbenzimidazole (0.5 M) for 2-methoxyproprionitrile (MPN) as co-solvent. Testing of DSSCs to analyze the influence of chain length (ethyl and heptyl) on cell efficiency revealed that, for silanes concentration of 1 M, electrolyte B (based on 2 in AN) and electrolyte C (based on 1 in MPN) gave the best cell efficiency at simulated full sunlight (AM 1.5, 1000Wm(-2)) illumination (5.0-5.3%). At 0.1 Sunlight (AM 1.5, 100Wm(-2)), electrolyte B gave the best performance of 8.0%. High open circuit voltages (V-oc) of 750-850 mV were achieved for a number of quite efficient cells (5-6%). For silane 2, variation of the I-/I-2 ratio and total silane content (1-2 M 2) on DSSC efficiency gave a consistent efficiency of 8.0% at 0.1 Sunlight. At full sunlight, the cell efficiency decreased as the silane concentration increased from 1 M (5.0%) to 2M (3.7%), largely due to a drop in short circuit current. (C) 2008 Elsevier B.V. All rights reserved.