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

Abstract

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 electrodeswere characterized using nitrogen gas sorption (NGS), x-ray diffraction (XRD), x-rayphotoelectron spectroscopy (XPS), energy dispersive x-ray spectroscopy (EDX), field emissionscanning electron microscopy (FEGSEM) and high resolution transmission electronmicroscopy (HRTEM). The change in the nanostructure was quantified and the thicknessesof the core–shell coatings determined. An evaluation of the dependence of thickness byHRTEM concluded that one coating step of either the indium or zirconium precursor gavethicknesses of 0.5 nm, with EDX and XPS confirming the presence of either In or Zr at theTiO2 electrode surface, respectively. These working electrodes were then used to fabricatedye-sensitized nanocrystalline solar cells (DSSCs) whose performance was tested under AM1.5G100 mW cm−2 illumination. TiCl4 post-treatment was found to improve the photovoltaic efficiencies from 3.6% to 5.3%. Single coatings ofeither In2O3 or ZrO2 on the TiO2 working electrode resulted in an increased efficiency from 3.6% up to5.0%. Thinner coatings gave the highest solar cell efficiency. The drop inperformance was mainly due to a decrease in short circuit current density(Jsc) with the greatershell thicknesses. ZrO2-coated TiO2 electrodes subjected to microwave heat treatment using a 2.45 GHz microwave produced thehighest efficiencies (5.6%) largely due to an increase in short circuit current from 11.4 to13.3 mA cm−2.