Abstract:
A series of highly efficient quasi-solid-state dye-sensitized solar cells (DSCs) is prepared by
harnessing the binary cation effect and positive effects of the selected performance enhancers
of gel-polymer electrolytes. The new electrolyte is composed of polyacrylonitrile polymer,
tetra-hexylammonium iodide (Hex4NI) and KI binary salts as well as 4-tertbutylpyridine and
1-butyl-3-methylimidazolium iodide performance enhancers.
The charge transport in the series of electrolyte is thermally activated and, accordingly,
temperature dependence of conductivity follows the VTF behavior. The enhancement of
conductivity is observed with increasing mass fraction of KI and decreasing mass fraction of
Hex4NI, while the total mass fraction of salts in the electrolyte is kept unchanged. The
highest conductivity of 3.74 mS cm-1 at ambient temperature is shown by the sample
containing KI only (without Hex4NI) at all the temperatures. The effects of dielectric
polarization of the electrolytes are studied by analyzing the frequency dependence of the real
and the imaginary parts of the AC conductivity in detail. Appropriate and reproducible cell construction are assured by exhibiting efficiencies above
5% by all the quasi-solid-state DSCs assembled using double-layered TiO2 photo-electrodes
and the new electrolyte series. Besides, highlighting the mixed cation effect, the cells with
mixed salts exhibited efficiencies greater than 6%. An impressively high efficiency of 7.36%
was shown by the DSC prepared with electrolyte containing 75 wt.% KI and 25 wt.%
Hex4NI. This study reveals that the salt combination KI and Hex4NI, which has not been
reported before, is a suitable binary iodide salt mixture to prepare highly efficient DSCs. The
replacement of tetra-hexylammonium ions by K+
ions improves the charge transport in the
electrolyte; however, the best solar cell performance is shown by the mixed salt system with
75 wt.% KI and 25 wt.% Hex4NI, which is not the highest conductivity composition.
Therefore, the exhibited high efficiency of 7.36% is evidently due to the binary cation effect.
