Comparison of the photoelectrochemical properties of RDS NiO thin films for p-type DSCs with different organic and organometallic dye-sensitizers and evidence of a direct correlation between cell efficiency and charge recombination

Undyed mesoporous NiO in the configuration of thin film (thickness 2–3 μm) presents photoelectrochemical activity as cathode of a p-type dye-sensitized solar cell (p- DSC) towards the reduction of triiodide to iodide under irradiation with a solar simulator. The photoelectroactivity of the oxide prepared via microwave plasma sintering (or rapid discharge sintering, RDS) has been observed in the spectral range 300–500 nm with the incident photon-to-current conversion efficiency (IPCE) reaching a maximum of 8.7 % at 375 nm. Upon sensitization, the characteristic photoelectrochemical activity of NiO can be either enhanced or depressed depending on the nature of the dye-sensitizer. The comparative analysis of the JV and IPCE curves of the p-DSCs based on bare NiO and four differently sensitized NiO cathodes reveals that N719, black dye (BD), and commercial squaraine 2 (SQ2) decrease the efficiency of conversion of dyed NiO with respect to bare NiO in the range of photoelectroactivity of Ni