Anatase TiO2 sols derived from peroxotitanium acid and to form transparent TiO2 compact film for dye-sensitized solar cells

Graphical abstract: Dye-sensitized solar cells with TiO2 nanocrystalline porous film in absence of compact film (A) and in presence of compact film in thickness of 1.0 μm (B), 2.5 μm (C), 4.0 μm (D), respectively. Highlights: → Anatase TiO2 sols were prepared by the hydrothermal treatment of peroxotitanium acid. → TiO2 sols were used for DSSC photoelectrode as the compact film on FTO layer. → The transmittance of the TiO2 compact film on FTO reached 80%. → The η of DSSCs in the presence of the compact film has improved significantly from 4.2% to 5.6%. - Abstract: Transparent and surfactant-free TiO2 sols containing anatase nanocrystals were prepared by the hydrothermal treatment of water-soluble peroxotitanium acid (PTA) at a temperature of 120 deg. C. The TiO2 nanocrystals were characterized by transmission electron microscopy (TEM). The TEM results indicated that the TiO2 nanocrystals were nanorod-like with diameters of less than 7 nm after the subsequently hydrothermal treatment. A gradient layer between the transparent fluorine doped SnO2 (FTO) layer and the porous titanium dioxide nanocrystalline film for dye-sensitized solar cells (DSSCs) photoelectrodes, was made with the as-prepared TiO2 sols. The TiO2 gradient layers were characterized by field-emission scanning electron microscopy and UV-vis absorption spectrometry. After the gradient layer deposition on the FTO coated glass, the composite multilayer film exhibited the visible light transmittance of 80% which approached to that of bare FTO glass. The photo-to-electric energy conversion efficiency of the N719 dye-sensitized solar cell had significantly improved from 4.2% to 5.6% in the presence of the compact layer between FTO and the porous TiO2 nanocrystalline film under of AM1.5 illumination (100 mW/cm2). The remarkable improvements in short-circuit current for the DSSCs was due to the effective gradient layer at the FTO-TiO2 interface which prevented direct contact of electrolytes with FTO and consequently reduced charge recombination losses.