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 mm) 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 the latter (300 500 nm) The fourth dye P1 represents the sole exception since its employment brings about an enhancement of the quantum efficiency of P1 sensitized vs. unsensitized NiO up to a maximum of 21 within the spectral interval of reference for NiO (300 500 nm) Outside the range of NiO photoelectrochemical activity, i.e. l 500 nm, only N719 does not introduce a gain of quantum efficiency with respect to bare NiO despite the observation of spectral sensitization up to 580 nm for N719 sensitized NiO. The impedance spectra recorded under illumination shows a direct proportionality between the overall efficiency (e) of the variously sensitized p DSCs and the amplitude of the semicircle which is generally associated with the process of charge recombination at the electrode/electrolyte interface with e decreasing with the increase of the recombination resistance.
Journal of Solid State Electrochemistry