Rational modification of TiO2 photoelectrodes with spinel ZnFe2O4 and Ag-doped ZnFe2O4 nanostructures highly enhanced the efficiencies of dye sensitized solar cells

To develop effective photoelectrode nanomaterials for dye-sensitized solar cells (DSSCs), spinel ZnFe2O4 (2.5, 5, 7.5, 10 wt%) and Ag-doped ZnFe2O4 (AgxZn1-x/2Fe2O4, x = 0.1, 0.2, 0.3, 0.4 mmol) nanomaterials were added into the TiO2 photoanodes. It was found that the DSSC fabricated with TiO2 + 5 wt% ZnFe2O4 exhibited the most improved efficiency of 3.89 % among the ZnFe2O4 containing devices. Furthermore, the power conversion efficiency (PCE) values were boosted when the Ag+ cations were doped into the ZnFe2O4 crystalline lattice. The greatest PCE = 5.75 % was achieved for the solar cell assembled using TiO2 + 5 wt% Ag0.2Zn0.90Fe2O4 photoanode indicating 47.81 % improved performance relative to that of the reference DSSC containing TiO2 + 5 wt% ZnFe2O4 photoelectrode. The electrochemical impedance spectra (EIS) approved that the DSSC with the TiO2 + 5 wt% Ag0.2Zn0.90Fe2O4 photoelectrode nanomaterial had the lowest charge transfer resistance but the greatest e-h recombination resistance at the interfaces of photoanode/dye/electrolyte. Hence, it had the quickest electron transport rate, and the greatest electron collecting efficiency in addition to the highest dye loading capacity and least photoluminescence (PL) intensity (charge recombination) which were all prominently beneficial for improvement of the DSSC performance.