Spray-deposited NiOx films on ITO substrates as photoactive electrodes for p-type dye-sensitized solar cells

Spray deposition followed by sintering of nickel oxide (NiOx) nanoparticles (average diameter: 40 nm) has been chosen as method of deposition of mesoporous NiOx coatings onto indium tin oxide (ITO) substrates. This procedure allows the scalable preparation of NiOx samples with large surface area (~103 times the geometrical area) and its potential for applications such as electrocatalysis or electrochemical solar energy conversion, which require high electroactivity in confined systems. The potential of these NiOx films as semiconducting cathodes for dye-sensitized solar cell (DSC) purposes has been evaluated for 0.3–3-μm-thick films of NiOx sensitized with erythrosine B (ERY). The electrochemical processes involving the NiOx coatings in the pristine and sensitized states were examined and indicated surface confinement as demonstrated by the linear dependence of the current densities with the scan rate of the cyclic voltammetry. Cathodic polarization of NiOx on ITO can also lead to the irreversible reduction of the underlying ITO substrate because of the mesoporous nature of the sintered NiOx film that allows the shunting of ITO to the electrolyte. ITO-based reduction processes alter irreversibly the properties of charge transfer through the ITO/NiOx interface and limit the range of potential to NiOx coatings sintered for DSC purposes.