Mesoporous titanium dioxide: sonochemical synthesis and application in dye-sensitized solar cells

Abstract

A novel method for shortening the synthesis time of mesoporous TiO₂ to 6 h is reported. Low-angle XRD and TEM showed that mesoporous TiO₂ with short-range ordered structures was synthesized when octadecylamine was used as a structure-directing agent and when Ti(OPrⁱ)₄ was used as a precursor. The highest surface area (853 m² g⁻¹) was obtained after extraction with a dilute solution of nitric acid. The material maintained a high surface area (467 m² g⁻¹) after calcination at 350°C, but the short-range ordered structures collapsed. XPS showed the interaction between TiO₂ and octadecylamine, while DSC, TGA, and FT-IR spectra showed the removal of octadecylamine by extraction and calcination. A mechanism for the fast formation of mesoporous TiO₂ is proposed. It is attributed to the formation of mesoporous material at high temperatures formed in the interface between the gas and bulk solutions resulting from ultrasound irradiation. Electrodes made from the mesoporous TiO₂ were tested in a dye-sensitized solar cell. The short-circuit photocurrent, open-circuit photovoltage and fill factor increased with an increase in the sintering temperature, having a performance threshold at 450°C, showing that the more ordered structures are required for high solar cell conversion efficiencies.