Ricerc@Sapienza

Screen-printed NiO electrodes were sensitized with 11 different dyes and the respective
electrochemical properties were analyzed in a three-electrode cell with the techniques of cyclic
voltammetry and electrochemical impedance spectroscopy. The dye sensitizers of NiO were organic
molecules of different types (e.g., squaraines, coumarins, and derivatives of triphenyl-amines and
erythrosine B), which were previously employed as sensitizers of the same oxide in dye-sensitized
solar cells of p-type (p-DSCs). Depending on the nature of the sensitizer, diverse types of interactions
occurred between the immobilized sensitizer and the screen-printed NiO electrode at rest and
under polarization. The impedance data recorded at open circuit potential were interpreted in
terms of two different equivalent circuits, depending on the eventual presence of the dye sensitizer
on the mesoporous electrode. The fitting parameter of the charge transfer resistance through the
electrode/electrolyte interface varied in accordance to the differences of the passivation action exerted
by the various dyes against the electrochemical oxidation of NiO. Moreover, it has been observed that
the resistive term RCT associated with the process of dark electron transfer between the dye and NiO
substrate is strictly correlated to the overall efficiency of the photoconversion () of the corresponding
p-DSC, which employs the same dye-sensitized electrode as photocathode.