Modification of mesoporous TiO2 electrodes by surface treatment with titanium(IV), indium(III) and zirconium(IV) oxide precursors:: preparation, characterization and photovoltaic performance in dye-sensitized nanocrystalline solar cells

Post-treatment of titanium dioxide (TiO2) films for use in dye-sensitized solar cells has been carried out with titanium(IV), indium(III) and zirconium(IV) oxide precursor solutions. The nanostructured electrodes were characterized using nitrogen gas sorption (NGS), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), energy dispersive x-ray spectroscopy (EDX), field emission scanning electron microscopy (FEGSEM) and high resolution transmission electron microscopy (HRTEM). The change in the nanostructure was quantified and the thicknesses of the core-shell coatings determined. An evaluation of the dependence of thickness by HRTEM concluded that one coating step of either the indium or zirconium precursor gave thicknesses of 0.5 nm, with EDX and XPS confirming the presence of either In or Zr at the TiO2 electrode surface, respectively. These working electrodes were then used to fabricate dye-sensitized nanocrystalline solar cells (DSSCs) whose performance was tested under AM1.5G 100 mW cm(-2) illumination. TiCl4 post-treatment was found to improve the photovoltaic efficiencies from 3.6% to 5.3%. Single coatings of either In2O3 or ZrO2 on the TiO2 working electrode resulted in an increased efficiency from 3.6% up to 5.0%. Thinner coatings gave the highest solar cell efficiency. The drop in performance was mainly due to a decrease in short circuit current density (Jsc) with the greater shell thicknesses. ZrO2-coated TiO2 electrodes subjected to microwave heat treatment using a 2.45 GHz microwave produced the highest efficiencies (5.6%) largely due to an increase in short circuit current from 11.4 to 13.3 mA cm(-2).