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The effect of a dense TiO 2 blocking layer prepared using the sol-gel method on the performance of dyesensitized solar cells was studied. The blocking layer formed directly on the working electrode, separated it from the electrolyte, and prevented the back transfer of electrons from the electrode to the electrolyte. The dyesensitized solar cells were prepared with a working electrode of fluorine-doped tin oxide glass coated with a blocking layer of dense TiO 2 , a dye-attached mesoporous TiO 2 film, and a nano-gel electrolyte, and a counter electrode of Pt-deposited FTO glass. The gel processing conditions and heat treatment temperature for blocking layer formation affected the morphology and performance of the cells, and their optimal values were determined. The introduction of the blocking layer increased the conversion efficiency of the cell by 7.37% for the cell without a blocking layer to 8.55% for the cell with a dense TiO 2 blocking layer, under standard illumination conditions. The short-circuit current density (J sc ) and open-circuit voltage (V oc ) also were increased by the addition of a dense TiO 2 blocking layer.

The effect of the addition of ionic liquids with four different cations (imidazolium, pyrrolidinium, piperidinium and pyridinium) on the performance of dye-sensitized TiO 2 solar cells based on electrolytes containing a tbutylpyridine (TBP) in 3-methoxypropionitrile (MPN) was studied. A total of 18 ionic liquids with mono-, diand tri-alkyl derivatives were used in the present study, and among them a pyridinium cation with a mono-alkyl group showed better cell efficiency than the others. The best photoelectric conversion efficiency, 7.213%, was obtained using 1-hexylpyridinium iodide with an open-circuit photovoltage (V oc ) = 0.731 V, a short-circuit photocurrent density (J sc ) = 16.175 mA/cm 2 , and a fill factor (ff) = 0.610 under AM1.5 and 100 mW/cm 2 illumination.

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