Alkoxysilane alkyl ammonium iodides have shown promise as electrolytes for DSSC’s, reaching open circuit voltages in excess of 800mV at 1 Sun. This concept has been extended to include a family of alkoxysilyl iodides containing piperidinium, pyrrolidinium and imidazolium cations and various length spacers to develop correlations between cation structure and the resultant effects on cell performance.
The synthesised ionic liquids were fully characterised using a wide range of physical techniques, including ¹H, ¹³C and ²⁹Si NMR, ESIMS, DSC, TGA as well as electrochemical ones including impedance and redox diffusion coefficients. The developed compounds were used as the sole iodide source for the construction of DSSCs and their performance therein was evaluated. Interestingly, the compounds containing an 11 carbon spacer between the siloxy functionality and the cation exhibited much higher open circuit voltages than the analogous 3 carbon compounds (Table I). In addition to the increased potentials obtained using the 11 carbon compounds, an increase was also witnessed to the current of the cells, although fill factors were significantly less than those found using the analogous 3 carbon compounds.
In addition to an increase in potential, the longer spacers also increased the electron lifetime within the cell, as demonstrated by electron lifetime measurements.
In conclusion, the developed compounds show good potential as iodide sources for DSSCs, with the longer carbon chains furnishing relatively high potentials and currents when compared to the analogous three carbon spacers.