Shorter nanotubes and finer nanoparticles of TiO2 for increased performance in dye-sensitized solar cells

Vertically aligned, reasonably dense, about 500 nm long TiO2 nanotubes (NTs) are prepared on transparent conducting fluorine-doped tin oxide (FTO) surfaces by a wet chemical procedure. The dye-sensitized solar cells (DSCs) fabricated using such active electrodes and N719 dye with usual I−/I3− electrolyte yield 2.46% solar-to-electricity conversion efficiency (η) without the TiCl4 treatment and 3.40% with the TiCl4 treatment, both at 1000 W m−2 simulated AM 1.5 irradiation. These values are higher and impressive for shorter NT arrays of ∼500 nm length. The successive introduction of TiO2 nanoparticles (NPs) by spraying into the NTs to form NT–NP composite films results in a linear increase of dye coverage. The variation of η as a result of NT–NP composite structure (with TiCl4 treatment) shows a gradual increase up to 8.53% at 1:2.2 NT:NP mass ratio, beyond which it slowly decreases.

► TiO2 nanotubes (NTs) of ∼500 nm length and 45 nm diameter were prepared by a chemical bath method.
► Dye-sensitized solar cells (DSCs) made with these NTs give 2.46% efficiency.
► TiCl4 treatment of NTs enhances the dye adsorption and hence the conversion efficiency.
► TiO2 nanoparticles (NPs) on the NT surfaces enhance the efficiency to 8.55%.
► For the same TiO2 mass, NT–NP combination gives higher efficiency than the NP alone system.