Open-circuit voltage improvement by using TiO₂ nanotubes as a working electrode of dye-sensitized solar cell

The titanium dioxide nanotubes (TiNTs) were directly fabricated from commercial P25 TiO₂ via alkali hydrothermal transformation. The optimized synthesis, thermal and hydrothermal stability, and consequent optical properties of the titanate nanotubes were systematically studied. The TiO ₂ nanotubes were characterized by transmission electron microscopy. Dye-sensitized solar cells (DSSCs) were constructed with films made of grown TiO₂ nanotubes as working electrodes. The nanocrystalline TiO ₂ pastes were prepared with PEG (Mw 20000) and as made TiO ₂ nanotubes. The titania thin films were grown by screen printing method in order to efficiently control the DSSC fabrication process. The microstructures of nanoporous films in solar cells were characterized by scanning electron microscope (SEM) and Brunauer Emmett Teller (BET) analysis. A metal-free organic dye (referred to as D102 dye) was used as a sensitizer. A high conversion efficiency of light-to-electricity of around 6% under illumination of simulated AM1.5 sunlight (65mW/cm²) was achieved with the TiO₂ nanotube cell. Compared with the case of DSSCs with TiO₂ nanoparticles, the open-circuit voltage and fill factor of DSSCs with TiO₂ nanotubes increased significantly. The related mechanisms are discussed.