Sponge-like TiO2 layers for dye-sensitized solar cells

A titanium oxide layer used in a dye-sensitized solar cell (DSSC) has to meet two opponent properties to enable high conversion efficiency: a large surface area (for high dye loading) and good connection between TiO₂ grains (for efficient extraction of electrons toward the front contact). In order to meet a trade-off between these criteria a preparation method for TiO₂ paste formulation based on Pechini sol–gel method and commercial nanocrystalline TiO₂ powder has been developed. A series of TiO₂ pastes with different molar ratios between titanium isopropoxide, citric acid and ethylene glycol (1:X:4X) in the paste have been examined. The structure and morphology as well as cross-cut tests of deposited and sintered TiO₂ layers have been analyzed. Results reveal that the paste with X = 8 exhibits the best properties, resulting in an overall conversion efficiency of DSSC under standard test conditions (100 mW/cm², 25 °C, AM 1.5G) up to 6.6% for ionic liquid based electrolyte.