Characterization of Screen-Printed Nickel Oxide Electrodes for p-type Dye-Sensitized Solar Cells

Mesoporous NiO films obtained via screen-printing deposition of a newly formulated paste containing preformed NiO-nanospheres have been employed as nanostructured photocathodes of p-type dye-sensitized solar cells (p-DSCs). The novel aspect of this contribution is the utilization of a diluted solution of weak acid as anti-aggregating agent of NiO nanoparticles during the preparation of the screen-printing precursor. Screen printed NiO cathodes of p-DSCs displayed photoactivity in both bare and sensitized states with overall efficiencies not higher than 0.05% when erythrosine b (ERY) was the colorant and I3-/I- the redox mediator. The charge recombination resistance of NiO photocathodes in the illuminated p-DSCs diminished from 230 to 90 Ω with the increase of cell efficiency in going from the pristine oxide to its ERY sensitized version. In absence of a redox mediator, the NiO electrodes here considered displayed electroactivity due to the occurrence of solid state oxidation processes in the range 0.1-1.0 V vs Ag/AgCl. From the modelling of the electrochemical impedance data the total electrical resistance Rtot of screen printed NiO decreased drastically in passing from the pristine (1*105 - 6*105 Ω) to the oxidized state (20 - 150 Ω). The fitting parameter Rtot combined the two terms of bulk transport and charge transfer at the NiO/electrolyte interface. Rtot depended on NiO film thickness and on the nature of the electrolyte in a non-straightforward manner for the verification of electrochemically induced processes of NiO film dissolution.