Synthesis of TiO2 hollow spheres using titanium tetraisopropoxide: fabrication of high efficiency dye sensitized solar cells with photoanodes of different nanocrystalline TiO2 sub-layers

Abstract

In this research TiO₂ hollow spheres with different diameters were prepared using titanium tetraisopropoxide (TTIP) as the TiO₂ precursor. Carbon spheres with average sizes of 230, 325 and 450 nm were prepared as the templates by hydrothermal method. Then TiO₂ was deposited on the surface of the carbon spheres through a liquid phase deposition (LPD) process. This two dimensional growth was performed in an appropriate concentration of TTIP and different LPD times. Finally the TiO₂ hollow spheres were achieved for specific LPD times by burning the carbon templates. Two kinds of TiO₂ nanocrystals with sizes around 20 nm were hydrothermally grown in acidic (pH = 1.5) and basic (pH = 10) autoclaving pHs. These nanocrystals were deposited onto FTO glass substrates and applied in the photoanode of dye sensitized solar cells. The layers were transparent and demonstrated a strong bonding to the FTO substrates. Three kinds of TiO₂ hollow spheres with external diameters around 310, 435 and 550 nm were also selected and used in a modified paste preparation process. They were finally deposited on the surface of transparent sub-layers of the TiO₂ NCs to enhance the light scattering. According to the results, an energy conversion efficiency of 9.7% was achieved for the cell with 2TA-1Sc photoanode. This photoanode was composed of two sub-layers of TiO₂ NCs prepared in acidic autoclaving pH and a layer of scattering hollow spheres. An efficiency of 9.4% was also attained for the cell with 1TB-1Sb photoanode including one layer of TiO₂ NCs prepared in basic autoclaving pH and a layer of scattering hollow spheres. These efficiencies represented an increase of about 39% and 118% compared to those of the cells with 2TA and 1TB photoanodes, respectively.