We report on a straightforward methodology to cover the FTO layer of the DSC photo anode with an insulating layer of nitro phenyl groups by electrochemical reduction of di(4-nitrophenyl)-iodonium tetrafluoroborate 1. The efficiency of the blocking layer was demonstrated by a ferrocene CV test, in which ferrocene CV peak separations increased from 200 to 400 mV, and in which the charge transfer resistance measured by EIS increased from 600 to 20.000 Omega depending on the number of grafting CV scans. Our DSCs displayed a V-oc increase of 182 mV at 90 W/m(2) corresponding to a reduction in the dark current with a factor of 1000, when using D5 as sensitizing dye, [Co(biPy)(3)](2+/3+) as mediator, and FTO | TiO2 as an electrode that had been grafted before by three CV scans of 1. However, DSCs prepared with N719 and D35 as dyes and using FTO | TiO2 as photoanode grafted with 1 showed decreased performance on all cell parameters.