Highly active nanocrystalline TiO2 photoelectrodes

Abstract

A simple method for the fabrication of highly photoactive nanocrystalline two-layerTiO2 electrodes for solar cell applications is presented. Diluted titaniumacetylacetonate has been used as a precursor for coveringSnO2:F (FTO) films withdense packed TiO2 nanocrystallites. The nanoporous thickTiO2 film follows thedense packed thin TiO2 film as a second layer. For the latter, amorphousTiO2 nanoparticles have been successfully synthesized by a sol–gel technique in an acidic environment withpH<1 and hydrothermal growth at a temperature of200 °C. The acidic nanoparticle gel was neutralized by basic ammonia and aTiO2 gel of pH 5 was obtained; this pH value is higher than the recently reported value of 3.1 (Park et al 2005 Adv. Mater. 17 2349–53). Highly interconnected, nanoporous, transparent and activeTiO2 films have been fabricated from the pH 5 gel. SEM, AFM and XRD analyseshave been carried out for investigation of the crystal structure and the size ofnanoparticles as well as the surface morphology of the films. Investigation of thephotocurrent–voltage characteristics has shown improvement in cell performancealong with the modification of the surface morphology, depending on pH of theTiO2 gel. Increasing the pH of the gel from 2.1 to 5 enhanced the overall conversionefficiency of the dye-sensitized solar cells by approximately 30%. An energyconversion efficiency of 8.83% has been achieved for the cell (AM1.5,100 mWcm−2 simulated sunlight) compared to 6.61% efficiency in the absence of ammonia in theTiO2 gel.