Incorporation of a fluorophenylene spacer into a highly efficient organic dye for solid-state dye-sensitized solar cells

A new efficient organic dye LEG4F, incorporating a fluorine-substituted phenylene unit in the π-spacer, has been synthesized and tested in dye-sensitized solar cells. Direct comparison with the parent dye LEG4 shows very similar performances in case of liquid electrolyte devices based on iodide/triiodide, yielding a power conversion efficiency of 6.8% under 1 sun and 8.0–8.2% under 0.5 sun illumination. However, LEG4F outperforms its fluorine-free analogue when the liquid electrolyte is replaced by the solid-state hole-transport material Spiro-OMeTAD, reaching 5.3% efficiency compared to 4.8% achieved by LEG4. We show that this improvement is due to the enhancement of the electron lifetime, which reduces recombination at the TiO2/dye/Spiro-OMeTAD interfaces.